Two Datasets of Questions and Answers for Studying the

arXiv:1712.09569v2 [cs.SE] 9 Jul 2018

Development of Cross-platform Mobile Applications

using Xamarin Framework

Matias Martinez

University of Valenciennes, France

Abstract

Context: A cross-platform mobile application is an application that runs on

multiple mobile platforms (Android, iO S). Several frameworks, have been pro-

posed to simplify the development of cross-platform mobile applications and,

therefore, to reduce development and maintenance costs. Between them, the

cross-compiler mobile development frameworks, such as Xamarin from Mi-

crosoft, transform the application’s code written in intermediate (aka non-

native) language to native code for each desired platform. However, to our

best knowledge, there is no much research a bout the advantages and disadvan-

tages of the use of those frameworks during the development and maintenance

phases of mo bile applications.

Objective: The objective of this paper is twofold. Firstly, to present two

datasets of questions and a nswers (Q&A) related to the development of mobile

applications using Xamarin. Secondly, to show their usefulness, we present a

replication study for discovering the main discussion topics of Xamarin devel-

opment.

Method: We c reated the two datasets by mining two Q&A sites: Xamarin

Forum and Stack Overﬂow. Then, for discovering the main topics of the ques-

tions from both datasets, we replicated a study that applies Latent Dirichlet

Allo c ation (LDA). Finally, we compared the disc overed topics with those topics

about general mobile development reported by a previous study.

Results: Our datasets have 85,908 questio ns mined from the Xamarin Fo-

rum and 44,434 from Stack Overﬂow. Between the main topics discovered from

those questions, we found that some of them are exclusively related to Xa marin

and Microsoft technologies such as the design pattern ‘MVVM’.

Conclusions: Both datasets with Xamarin-related Q&A can be used by

the research community for understanding the main concerns about developing

cross-platform mobile applications using Xamarin framework. In this paper, we

used it for replicating a studying about topic discovering.

∗

Corresponding author

Email address: matias.martinez@univ-valenciennes.fr (Matias Martinez)

Preprint submitted to Elsevier July 10, 2018

Keywords: Mobile Development, Cro ss-platform mobile applications,

Questions a nd Answers, Topic modeling, Xamarin

1. Introduction

Nowadays, there are billions of smartphone devices around the world. Smart-

phones are mo bile devices that run software applications (apps) such as games,

social network and banking apps. A native mobile application is an app built

to run in a particular mobile platform. Currently, there are two platforms that

dominate the smartphone market: Android (from Google) and iOS (from Ap-

ple), with the 99.7% of the market share as of the ﬁrs t quarter of 2017 [19].

A cross-platform mobile application is an application that targets more than

one mobile platform. To cover a large number of users and, thus, to increase the

impact on the market and revenues, companies and developers aim at releasing

their mobile apps to both Android and iOS platforms. A tr aditional approach for

developing this k ind of apps is to build, for each platform, a native application

using a particular programming language (e.g., Java for Android, Objective-C or

Swift for iOS), SDK (Software Development Kit) and IDE (e.g., Android Studio,

XCode for iOS). Unfortunately, this approach increa ses the cost of development

and maintenance. For example, a company needs developers with diﬀerent

competence for developing an app fo r two platforms, resulting in two native

apps. Moreover, as studied by previous works, those native apps co uld have

diﬀerent quality. For example, Hu et al. [18] found that 68% of the studied

cross-platform apps have diﬀerent start ranking across the App Store and Google

Play stores. Furthermore, Ali et a l. [2] analyzed 80,000 c ross-platforms apps

from those app stores and found that the Android version of app-pairs receives

higher user-perceived ratings compared to the iOS version.

During last years, researches (e.g., [29]) and industry companies (e.g, Mi-

crosoft, Facebook Inc.) have both focus e d on proposing development frame-

works with the goal of making easier the development and ma intenance of

cross-platforms mobile apps. Earliest frameworks focuse d on producing hy-

brid mobile applications: apps built coding both non-native (e.g., HTML for

Phonegap/Cordova

) and native code. The non-native code is shared acro ss all

the platforms’ implementations, whereas the native is written for a particular

platform. Nonetheless, beyond the good results of some of them for developing

simple apps ([20, 15]), companies such as Facebook found the resulting appli-

cations do not have the same user experience than purely native applications

[24].

Another family of fr ameworks for developing cross-platform apps is the cross-

compiler mobile development framework. They generates native code (for a

particular platform) from an application written in a non-native language. Xa-

https://cordova.apache.org

marin

and React-Native

are two of them, which consider C# and JavaScript

as non-native lang uages, res pectively. Using cross-c ompiler frameworks for de-

veloping cr oss-platform mobile applications, developers can reduce both devel-

opment and maintenance costs by sharing code between the diﬀerent platform

implementations and, at the same time, they obtain pure native mobile appli-

cations.

However, beyond the advantages of sharing code, we wonder whether devel-

oping cross-platforms apps using c ross-compiler frameworks has any drawback

with respect to the na tive development during the life-c ycle of a mobile ap-

plication. To our knowledge, as also mentioned by [26], no pr evious work has

studied that yet. Our long ter m goal is to study the diﬀerence s between the

development process that use s cross-compiler framework and the process that

uses traditional development to olkits.

To encourage the study of cross-platforms mobile a pplication, this paper

presents two datasets of questions and ans wers (Q &A) related to one cross-

platform development framework: Xamarin from Microsoft.

The two datasets are confor med by questions and answers extra c ted from

Stack O verﬂow and Xamarin Forum, respec tively. The la tter is a Q&A site

exclusively dedicated to Xamarin technology.

The main reasons that moti-

vate us to s tudy Xamarin are: a) availability of documentation and guidelines

;

b) 5+ books edited during last years (e.g., [16, 35, 28]); c) development toolkits

available

; d) availability of tes ting environment for cross-platform apps called

Xamarin Test Cloud.

, and e) Xamarin is one of the top 10 most popular de-

velopment fr ameworks and libraries according to the Stack Overﬂow Survey

2018.

Previous works have analyzed mobile-related Q&A from Stack Overﬂow with

diﬀerent purposes, for instance, for discovering main topics related to mobile de-

velopment ([23, 34, 7]). To show the utility of the two Xamarin-related Q&A

dataset, in this pap er we replicate one of those studies, i.e., Rosen and Shihab

[34], focusing exclusively on the Xamarin technology, instea d of focusing on gen-

eral mobile development as done by Rose n and Shihab. Our study discovers the

main discussion topics present in the ques tions related to Xamarin by applying

Latent Dirichlet Allocation (LDA). Finally, to know about the particularities

of cross-platform apps developed using Xamarin, we compare the topics we dis-

covered with those topics related to general mobile development discovered by

Rosen and Shihab.

Our research is guided by the following research questions:

https://www.xamarin.com

https://facebook.github.io/react-native

https://forums.xamarin.com/

https://developer.xamarin.com/guides/

https://docs.microsoft.com/visualstudio/

https://www.xamarin.com/test-cloud

https://insights.stackoverflow.com/survey/2018/#technology-frameworks-libraries-and-tools

RQ 1: What is the number of a) Xamarin-re lated questions, b) a nswers

and accepted, c) views on Stack O verﬂow and Xamarin Forum?

RQ 2: What are the main topics dis c ussed about Xamarin in Q&A sites?

RQ 3: How many main topics from Stack Overﬂow and Xamarin Forum

are also topics related to general mobile development discovered by Rosen

and Shihab?

RQ 4: What are the most relevant questions fro m Xamarin-related topics?

The contributions of this pap e r are:

1. A dataset of Q&A related to Xamarin technology ﬁltered from Stack Over-

ﬂow.

2. A dataset of Q&A extracted from Xamarin forum.

3. An analy sis of the two datasets (e.g., number of questions, answers, views).

4. Discussion topics discovered from questions related to Xamar in technol-

ogy.

5. An study about the relation between topics fr om Stack Overﬂow and Xam-

arin Forum and those topics discuss e d in questions related to development

of native mobile applications from [34].

6. The study of the re levant questions from 3 Xamarin-related topics.

The paper is organized as follows. Section 2 discusses the rela ted work.

Section 3 presents two datasets of Q&As extracted from Stack Overﬂow and

Xamarin Forum. Section 4 analyzes both datasets in terms of number questions,

answers accepted, and views. Section 5 replicates the study of Rosen and Shihab

[34] for discovering topics from Stack Overﬂow and Xamarin Forum. Section 6

presents the discussion. Section 7 concludes the paper.

All data discussed in this paper , including the two Q&A datasets, is publicly

available in our web appendix: http://anonymous.4open.science/repository/3ac646ee-03f9-40d0-a7fc-d0a6124af979/

2. Related Works

During the recent years several works have studied Q&A from the site Stack

Overﬂow [3 , 6 , 30, 31]. Some of them focused on questions abou t Android plat-

form [22, 43, 36, 7, 8, 1 , 40, 39]. For example, Linares-Vasquez et al. [22] studied

questions and activities in Stack Overﬂow when changes on Android APIs occur,

ﬁnding that dele ting public methods from APIs is a trigger for questions that are

discussed more. Wang et al. [43] analyze d posts from Stack Overﬂow related to

iOS and Android APIs to ﬁnd API usage obstacles, and then they applied a topic

modeling technique to discover several repetitive scenarios in which API usage

obstacles occur. Stevens et al. [36] studied questions about Android permission

use on Stack Overﬂow. Other works have focusing on mobile-related tags from

Stack Overﬂow: Beyer et al. [7] investigated 450 Android-related posts from

Stack Overﬂow to get insights into the issues of Android app development. To

our knowledge, no work has studied Stack Overﬂow questions and problematic

related to neither c ross-complied frameworks nor Xama rin technology.

In this paper, we analyze Q&A related to Xamarin technology, and then

we apply applied a topic modeling techniques called Latent Dirichlet Allo c ation

(LDA) to obta in the main topics from those questions. As reported by Chen et

al. [10] and Sun et al. [37] several works have already a pplied topic modeling

techniques such as LDA. For instance, Barua et al. [5] analyzed Stack Overﬂow

data to automa tically discover the main topics present in developer discussions.

Yang et al. [44] focused on discovering topics related to security by a nalyz-

ing sec urity-r e lated posts. Bajaj et al. [4] discovered topics from discuss ions

about web developers and focused on how preva lent ar e web-related topics in

discussions related to mobile web development. Other works have focused on

topic mo deling for native mobile technologies. For example, Linares-Vasquez et

al. [23] used LDA to extract hot-topics from mobile-development related ques-

tions. Their ﬁndings suggest that most of the questions include topics rela ted to

general questions and compatibility issues, whereas the most s peciﬁc topics are

present in a reduced set of questions. Rosen and Shihab [34] applied LDA on

mobile-related Stack Overﬂow posts to determine what mobile developers are

asking. Acros s all native platforms studied, they found that ques tions related to

app distribution, user interface, and input are among the most popular. Pinto

et al. [33] have analyzed questions about Swift, programming languag e (suc-

cessor of Objective-C) for building native iSO mobile apps. They applied LDA

to ﬁnd common problems faced by Swift developers, ﬁnding that the language

is easy to understand and adopt, but there are many questions about problems

in the to olkit (IDE, SDK). In our work, we focus on to pics related to Xamarin

development framework.

Other works have study both Stack Overﬂow and other sources of infor-

mation. For example, Wang et al. [42] studied the mutual knowledge sharing

between Android Issue Tracker and Stack Overﬂow. Their goal is to bridge

the two communities by linking related issues to posts automatically. Ye et

al. [45] s tudied how users share URLs in Stack Overﬂow for understanding

how knowledge diﬀusion process takes place on that site. They found that the

31% of the shared URLs on Stack Overﬂow is to reference information that can

help to solve a complex problem. Other works focus on analyzing developer

forums. For example, Venkatesh et al. [41] mined both develop er forums and

Stack Overﬂow to ﬁnd the common challenges encountered by developers when

using Web APIs. As diﬀerence with our work, they put all posts (from both

Web APIs and Stack Overﬂow) in a same dataset, which is later used for ex-

tracting topics using LDA. Lee et al. [21] studied the similarity in developer

interests within and across GitHub and Sta ck Overﬂow. They found that the

39% of the GitHub repositories and Stack Overﬂow questions that a developer

had participated fall in the common interests. Zagalsky et al. [46] focused on R

language by analyzing questions and answers from two channels: the R-tag in

Stack Overﬂow and the R-users mailing list. They found that knowledge is con-

structed in each channel in a diﬀerent manner: on Stack Overﬂow participants

contribute knowledge independently o f each other, whereas R-user mailing list

are more likely to build on other answers. In this work, we cre ate two datasets

of Q&A related to Xamarin technology, that could be used for replicating some

of these works (e.g., [4 6]).

Other works focus on classifying, compar ing and evaluating cross-platform

mobile application development tools to build hybrid mobile and native apps

([15, 14, 12, 27, 13]). For example, Ciman et al. [11] analyzed the energy

consumption of mobile development: their results showed the adoption of cross-

platform frameworks as development tools always implies an increase in energy

consumption, even if the ﬁnal application is a real native application. I n that

work, Xamarin fra mework was not evaluated. To the best of our knowledge,

no work has studied c ross-platforms mobile applica tions created with Xamarin

framework. In this work we study questions from Q&A to understand the main

problematic faced by developers when they develop cross-platforms mobile apps

using Xamarin framework.

3. Creation of two datasets with Q&A about Xamarin

In this section, we present two datasets with questions and answers (Q&A)

related to Xamarin technology. In section 3.1 we present the ﬁrst dataset that

is co mposed of posts extracted from the site Stack Overﬂow.

In section 3.2

we present the second dataset, named XamForumDB, is composed of posts

extracted from the oﬃcial forum of Xamarin.

Finally, in section 4 we brieﬂy

describe the data from both datasets. In section 5 .2 we use both datasets for

extracting the main discussion topics related with Xa marin technology.

3.1. Dataset of Q&A from Stack Overﬂow

3.1.1. Data Description

We used the data dump of Stack O verﬂow provided by Stack Exchange,

Inc.

The data is organized on 8 XML ﬁles, each one r e presents one data entity:

Posts, Users, Comments, Tags, Votes, PostLinks, PostHistory, and Badges.

For facilitating the manipulation o f the data, we migrated it to a relational

dataset.

A post from the Stack Overﬂow data dump corresponds to a question or an

answer done by an user. Question can have zero or more tags (up to 5). A

post can also have a vote, which represents a mark as ‘favorite’, ‘spam’, ‘inform

https://stackoverflow.com/

https://forums.xamarin.com/

https://archive.org/details/stackexchange

https://ia800500.us.archive.org/22/items/stackexchange/readme.txt

https://gist.github.com/gousiosg/7600626

Table 1: Tags used for detecting questions related to Xamarin. The technique for ﬁltering

tags is described in [34]. The table shows the total occurrence of the tag in all posts, in posts

tagged with 1+ tag from the ﬁnal set of tags, and two measures TRT and TST used by the

technique for ﬁltering tags. The table shows the ten tags with hi ghest number of posts.

Tag Name

Occurrences

TRT TST

All posts Xamarin posts

xamarin 25029 25029 100% 100%

xamarin.ios 10640 10640 100% 42,51%

xamarin.android 9590 9590 100% 38,32%

xamarin.form s 9308 9308 100% 37,18%

mvvmcross 2881 2003 69,52% 8,00%

xamarin-studio 1355 1355 100,00% 5,41%

monodevelop 2430 696 28,64% 2,78%

portable-class-library 1355 502 37,05% 2,01%

monotouch.dialog 461 428 92,84% 1, 71%

xamarin.mac 386 386 100,00% 1,54%

... ... ... ... ...

moderator’, ‘oﬀensive’, etc. The Stack Overﬂow data set contains 14,458,875

questions and 22,668,556 answers.

3.1.2. Methodology to ﬁlter Xamarin post s from Stack Overﬂow

The ﬁrst challenge is to ﬁlter posts related to Xamarin technology among

all posts present in the Stack Overﬂow data dump. For that, we apply two

techniques. The ﬁrst one ﬁlters posts according to the tags associated to each

post. The second technique matches keywords from the posts’ titles. Let us

detail each strategy.

Filtering posts by tags. We used the technique proposed by Rosen and Shihab

[34], who ﬁltered posts r elated to mobile technologies. Their technique consists

of three steps. The ﬁrs t step ﬁlters posts using a initial set of tags (in that work

the author used mobile related tags such as ‘Android’, ‘iOS’). The seco nd step

analyzes the most re presentative and signiﬁcant tags from the posts retr ieved

after applying the ﬁrst step. Finally, the last step ﬁlters posts from Stack

Overﬂow using the most representative tags for the mobile technology (those

tags discovered in the previous step).

We applied the technique as follows. In the ﬁrs t step we deﬁned the initial

set of tags: as we aim at ﬁltering Xamarin-r elated posts, our initial set was

“%xamarin%”, where % corresponds to zero or more chara c ters. In total, 28

tags include the word ‘xamarin’ such as ‘xamarin.iso’, and formed the initial set

of tags. We then retrieved 39,855 questions tagged w ith at least one tag from

the initial set. T hose 39,855 questions have, in total, 4,143 ta gs. Note that,

those retr ieved posts could also be tagged with tags that are not included in the

initial set, but they are related to Xamarin technology such as ‘monodevelop’.

To obtain tags related to the Xamarin technology not included in the initial set,

Data dump released the August 31, 2017

the technique by Rosen and Shihab presents two measures, TRT (tag relevance

threshold) and TST (tag signiﬁcance threshold) [34], that help us to: a) obtain

those tags representative to Xamarin technology, and b) discard those tags that

are related to Xamarin technology but, at the s ame time, they are to o general.

For instance, a signiﬁcant por tion of Xamarin posts are tagged with "Android".

However, most of the q uestions tagged with Android are not related to Xamarin

technology.

TRT(tag

) is the ratio between the number of posts that contain at least one

tag fro m the initial set and the total number of pos ts related to tag

. TST(tag

)

is the ratio between the number of mobile posts for tag

and the number of

mobile posts for the most popular mobile tag.

In the second step, we ﬁltered those tags with at least a 25% for represen-

tative (TRT) and 0.1% fo r signiﬁcance (TST). In total, 38 tags conforms the

ﬁnal set of tags related to Xamarin technology. Table 1 shows the 10 tags with

higher number of posts, and for each tag the number of total occurrences on

a) all posts and b) on Xamarin posts, and the measures TRT and TST. For

example, the ﬁnal tag set includes tag "monotouch.dialog", which has a TRT

of 92.84%: almost all posts tagged with that tag are also tagged with one tag

from the initial tag set such as ‘Xamarin’. Moreover, those pos ts represent the

2.34% (i.e., the TST value) out of all posts tagged with at least one initial tag.

On the contrary, the tag ‘Android’ is not included in the ﬁnal tag set: its TRT

metric is lower that the threshold we set: only the 1.07% of post tagged with

Android also are tagged with Xamarin (i.e., TRT metric).

Finally, fo r the third step of the technique, we retr ie ved 43 ,988 posts related

to Xamarin technology: 39,855 of them ta gged with the initial tags (i.e., include

the keyword "Xamarin" ) and 4,133 posts tagge d with at least one tag from

remaining ﬁnal set of ta gs.

Filtering posts by keywords. The second technique for retrieving Xamarin-related

posts ﬁlters posts by matching keywords on the post’s title. This strategy aims

at retrieving those posts that are not tagged with any tag fr om the ﬁnal set of

tags. We deﬁne a keyword for each tag included in ﬁnal set of tags presented

befo re.

Using this keyword-based strategy, we retrieved 446 new posts related to

Xamarin technology. For instance, one of them is the post "Xama rin Android

Save sms" (post id 2940542 0)

which was tagged with 3 tags: "C#, android,

datetime", none of them included in our ﬁnal set of tags.

Final set of Xamarin-related posts from Stack Overﬂow. Using the two de-

scribed techniques, we retr ie ved 44,434 questions from the Stack Overﬂow dump:

43,988 were found using the tag-based strategy, whereas 446 were found using

the keywords-based strategy.

https://stackoverflow.com/questions/29405420/xamarin-android-save-sms

3.2. XamForumDB: a dataset with questions from Xamarin Forum

3.2.1. Describing Forum Xamarin

The Xamarin Forum is an online web platform where mobile developers post

questions or start a discussion about the Xamarin framework and its ecosystem.

Moreover, it is a communication channel between the developers of the frame-

work (a.k.a. Xamarin Team) and users (i.e., the develop ers of mobile apps that

use Xamarin). Fo r instance, new versions of the framework or of particular

components are announced in the forum.

All posts are publicly available.

However, for creating a new post, user s must be registered into the site, which

is free .

Forums. The Xamarin Forum site is composed o f s e ven general forums: Com-

munity, General, Pre-release & Betas, Tools and Libraries, Graphics & Games,

Xamarin Platform and Xamarin Products. For instance, the forum Xamarin

Platform contains questions related to the development of an application for

diﬀerent targeted platforms , while the forum Xamar in Product focuses on dis-

cussions about products related to the Xamarin technology s uch as TestCloud, a

cloud-based platform for testing mobile apps built using Xamarin. Each of those

forums has one or more ‘sub-forums’. For insta nce , the mentioned Platform fo-

rum has 5 categories: Android, iOS, Cr oss-Platform, Mac, and Xamarin.Forms.

The forums are created by the forum administrato rs, w hich means that users

are not able to deﬁne new ones.

We identify two types of forums: 1) thos e related to technological topics

(platforms, libraries, too ls, IDEs, etc.) and 2) those related to non- technological

topics related to Xama rin (events, conferences, jobs, etc.).

The main page of each fo rum shows a paged-list of posts and two buttons,

one for creating a ques tion and the other for creating a discussion. Each post

from the list shows the post’s title, author, number of views, number of answers,

and zero or more labels. Those labels are colore d boxes loc ated near the title

and indicate, for instance, if a question was answered o r if the answered was

accepted by the user who wro te the question.

Posts. A user can create a post on a given categ ory. Even there are two types

of posts, i.e., questions and discussions, the creation forms of them are similar,

i.e., both have the same ﬁelds. The user can also se lect a list of tag s associated

the new post. However, once a post is created, the forum does not show the list

of tags associated to a pos t.

Answers. A registered user can answer an existing question or to put a ‘like’

on existing answers. Moreover, as in others Q &A such as Stack Overﬂow, the

post’s author can accept one or more answers. The accepted answers are labeled

with a green-colored box tag “Accepted answer".

https://forums.xamarin.com/discussion/85747/xamarin-forms-feature-roadmap#latest

Last visit: June, 2018

Users. The Xamarin Forum provides the forms for registering new users, which

have the right to create new posts and to write comments. In the forum also

participate users that belong to the organization that develops Xamarin frame-

work.

3.2.2. Dataset construction

The Xamarin Forum site does not have an API to programmatically access

and retrieve the data, such as those provided by Stackoverﬂow

and GitHub

For this reason, we developed a web crawler for retrieving and stor ing all pages

from Xamarin Forum. Our engine has main two phases: 1) Page fetching and

2) Page parsing.

Fetching pages. The ﬁrst phase fetches (i.e., downloads) all web pages written in

HTML from the forum web site https://forums.xamarin.com/, by accessing

via HTTP protocol. The Xamarin Forum has two kinds of web pages. A page

from the ﬁrst kind corresponds to a single post. It contains the pos t’s title,

question (or discussion topic), author data (names, location, roles ), posting

date and a list of comments. Each comment has the name o f the user tha t

wrote it, the date, and one or more labels such as “Answered question". The

second kind of pages corresponds to the main pages of each forum. A “main"

page shows in a paged list all posts done in that forum

, ordere d by decreasing

creation date. The list shows for each post its title, the numbers of views (i.e.,

number of visits the po st has received), numbe rs of comments done, and zero

or mo re labels that indicates if the post is a question or announcement, if it has

an accepted answer, etc.

Extracting data from pages. In the se c ond phase, our engine extracts and format

data for each fetched page and store it in a relational database. Our engine

is implemented in python language, and uses the library BeautifulSoup

for

parsing the Xamarin web pages in HTML. The structured data is then stored

in a MySQL database.

3.2.3. Data schema

The store all data extracted from the Xamarin forum in a relational database.

We now descr ibe brieﬂy the main entities from the database schema. T he ﬁrst

entity is Post, which stores all posts written in the Xamarin forums. Each

post belongs to one Forum and has zero or mor e Comments. Note that the post

entity stores both questions and discuss ions. We decide to model both questions

and discussion in the same entity due they share most of their properties. Both

Comment and Post entities have a relation many-to-one with the entity User,

which stores the information of the users that make or answer a post. A User

https://api.stackexchange.com/

https://developer.github.com/v3/

In those m ain pages, those posts are called ‘Threads’

https://www.crummy.com/software/BeautifulSoup/bs4/doc/

has diﬀerent Roles. A register e d user has the role ‘Member’ by default, but there

are other roles exclusively assigned to used belonging the Xamarin organization

such as ‘Forum Administrator’, or role ‘XamUProfessor" which are professionals

involved on the Xamarin training program called Xama rin University.

3.3. Perspectives of Xamarin Forum and Xamarin-related posts from Stack Over-

ﬂow

In our o pinion, both datasets can be used by the research community for

understanding the main concerns about developing cro ss-platform mobile appli-

cations using Xamarin framework. In this paper we use them to discover the

main discus sed topics from their questions.

4. Analyzing datasets with Q&A related to Xamarin technology

In this section we describe and compare the two datasets with questions and

answers related to Xamarin technology presented in section 3 with the goal of

answering the ﬁrst research question: What is the number of a) Xamarin-related

questions, b) answers and accepted, c) views on Stack Overﬂow and Xamarin

Forum?.

4.1. Number of questions

The Xa mForumDB has 91,838 questions.

The ﬁrst dates from January, 29

2013, and the last one from September, 6 2017 . There are 85,908 (93.5%) ques-

tions related to technological forums, a nd 5,930 (6.5%) related non-technological

forums such as Events has 1,079 questions (1.17%), Job Lis tings 465 (0.51%).

In this work, we are interested on those technological questions, discarding the

non-technological for fur ther analyses.

In Stack Overﬂow we selected 44,434 questions discussing a bout Xamarin

technology. They represent around the 0.12% of all questions from Stack Over-

ﬂow, which has 37,215,528 ques tions. Compare d to other cross-platform mobile

app development frameworks, the number of questions has the s ame o rder of

magnitude. For instance, 2 1,515 questions were tagged w ith "%react%native%"

(framework for generating native mobile apps using JavaScr ipt language), 60,790

questions were tagged with "%cordova%" and 8,194 "%phonegap%" (Apache

Cordova/Phonegap, is a framework for creating hybrid mobile apps using HTML

and JavaScript).

https://www.xamarin.com/university

In this paper, we use the terms ‘question’, ‘post’, and ‘thread’ interchangeably.

Data corresponding to dump from August 31, 2017.

4.2. Number of answers and acceptance

On Xamarin Forum, the 72.3% (62,114 o ut of 85,908) of the technological

questions have at least one answer. In average, each ques tion has 2.99 answers.

The remaining 29.7% (23,794) has not been answered. Moreover, the 15.2%

(13,025 out of 85,908) of the questions have, at least, accepted answer. The

proportion of answered questions is similar in Stack Overﬂow and Xamarin

Forum: 79% vs 72.3%. However, the propo rtion of accepted answers on Stack

Overﬂow is 3 times as larger as that one from Xamarin forum: 46.1% vs 15.2%.

On Stack Overﬂow, the 79% (35,10 0 out of 44,434 ) has at least one answer.

In average, each question has 1.13 answers. The 46.1 % (20,495 out of 44,434)

of Xamarin questions has one accepted answer, whereas the 33.9% (14,605) ha s

at least one answer but any on them was accepted. The remaining 20% (9,334)

has not been ans wered.

4.3. Number of views per question

Xamarin-related questions from Stack Overﬂow were viewed 36,523,008 times,

821.9 views per question as average, whereas those from Xamarin Forum were

viewed 35,032 ,568, that is, 407.8 views per question as average. In conclusion,

questions from Xamarin Forum have received almost the same number of views

than Xamarin-related questions fro m Stack Overﬂow (>35 millions). However,

Stack Overﬂow questions are viewed, in avg., two times more that those from

Xamarin forum.

Respo nse to RQ 1: What is the number of a) Xamarin-rel ated

questions, b) answers and accepted, c) views on Stack Overﬂow

and Xamarin Forum? a) Xamarin forums has a 85,908 questions re-

lated to Xamarin and Stack Overﬂow ha s 44,434. b) The proportion of

answered questions is similar in Stack Overﬂow and Xamarin Forum (79%

vs 72.3%), however, the propo rtion of accepted answers on Stack Overﬂow

is ∼3 times as larger (46.1% vs 15 .2%); c) Questions of both sites have

received almost the same number of views (>35 millions), however, thos e

from Sta ck Overﬂow are viewed, in avg., two times more.

5. Replication study over the two datasets: topic modeling

In this section, we present an study that replicates the experiment replicates

the study of Rosen and Shihab [34]. T hat work focuses at discovering topics

from mobile development (i.e., not related to neither a particular platform nor

framework) from Stack Overﬂow. On the contrary, our study aims to discover

topics from Xamarin-related questions from Stack Overﬂow and Xamarin Fo-

rum. In addition, our replication study compares those Xamarin-related topics

with those found by Rosen and Shiha b. This section is organized as follows: In

Section 5.1 we ﬁrst introduce the methodology to discover topics (based on that

one from Rose n and Shiha b), and in Section 5.2 we then present the results.

In the rest of this paper, w hen the mention Stack Overﬂow questions we refer

to the dataset of questio ns from Stack Overﬂow related to Xamarin technology

that we built in section 3.1, whereas Xamarin Forum questions are those from

the XamForumDB built in sectio n 3.2.

5.1. Methodology for replicating an experiment about topic modeling

In this section, we present three methodologies that we execute to respond

the research questions. First, in section 5.1.1 we prese nt a methodology for dis-

covering the discussion topics from questions from Stack Overﬂow and Xamarin

Forum (i.e., from the datasets we presented in sections 3.1 and 3.2). The re sults

will us allow to respond the second research question. Then, in section 5.1.2

we present a methodology for relating topics discovered from diﬀerent sources.

We use it to respond the third research question. Fina lly, in section 5.1.3 we

introduce a methodology for retrieving re le vant questions from a to pic and we

use it to respond the forth r e search question.

5.1.1. Methodology for Discovering Topics

This section presents a methodology for discovering the main topics from

a dataset of questions. We applied this procedure for obtaining two sets of

main topics: one from Stack Overﬂow questions, another from Xamarin Forum

questions.

The methodology consists of the following steps.

Retrieve posts t itles. For each question from a datase t (Xama rin Forum or Stack

Overﬂow), we created a document that includes all words contained in the ques-

tion’s title as done by Rosen and Shihab [34]. In case of Xamarin Forum, we

only considered the technological posts (i.e., the 93.5% of all posts), a s discussed

in Section 3.1.2.

Docu ment processing. We pre-processed all documents by ﬁrst removing stop

words (e.g., "at", "the") and then applying a customized word stemming pro-

cessing. During the setup of our experiment, we noted that traditional stem-

ming (as applied by, for example, [23]) alternated domain-speciﬁc words such as

“iOS" or “Mono", and, by c onsequence, the step produces a loss of informatio n.

With the goal of minimizing the impact of traditional stemming, we deﬁned a

customized word stemming process composed by the following steps. We ﬁrst

created a list of words related to the Xamarin technology. Those words are

the tags related to Xamarin posts presented in section 3.1.2. The list, called

technology-speciﬁc words list, is available in our appendix. Words from a post

title tha t belong to that list are not stemmed a nd they are included in a docu-

ment without any transformation applied. For the words that are not included

in the list, we applied the ﬁrst step of the stem process described by [32] for

transforming all words in sing ular.

Discovering topics. We applied Latent Dirichlet allocation (LDA) algorithm as

done by Blei et al. [9] for discovering topics from a set of documents, where

each document corresponds to a pre-processe d question’s title. Several works

have used LDA for discovering main topics in the doma in of, for example, web

development [4], software maintenance [38], and mobile development ([34, 23]).

As output, LDA produces a set of topics, each composed of a list of pairs

word-probability. Typically, previous works represent a topic with the 15 or

20 words with highest probability ([23] and [34], respectively). We used an

implementation of LDA called Mallet [25].

One o f the challenge of LDA to chose a conﬁguration (i.e., values for the input

parameters) that produce meaningful topics. There are four main para meters

to conﬁgure: a) alpha, b) beta, c) number of topics to generate, and d) number

of iterations. In this experiment, we used a similar conﬁg uration proposed by

Rosen and Shihab [34], one of the closest related work, w hich studied what

mobile developers are asking about on Stack Overﬂow. The conﬁguration they

used is: 40 topics to generate (nrtopics), alpha = 0.025 (that is: 1/nrtopics);

beta = 0.1 and number iterations = 1000. Having similar conﬁguration to Rosen

and Shihab allows us to compared the topics we discovered from Xamarin-related

questions, with those fr om na tive mobile apps discovered by them [3 4] (sec tion

5.2.2).

In the remaining of the paper, we refer as t

and t

xam

, to topics with

identiﬁer N

from Sta ck Overﬂow and Xamarin, respectively.

Labeling topics. As each topic discovered from LDA is a list of words, previous

works labeled each topic with a human readable la bel. In this work we decided

to reuse, when is possible, labels related to mo bile technology deﬁned by Rosen

and Shihab [34], which discovered and labeled topics related to mobile devel-

opment. Some of the labe ls from this work are “Input”, “Tools ”,“Application

Store”, “ Parsing”, “Map and Location”. In case that none of their lab e ls describe

correctly a topic that we discovered, we deﬁned a new lab e l by taking into ac-

count the words from the topic and their probabilistic. In some cases we used

the same labe l for two rela ted topics a nd included a sub-category in parenthesis

for remarking the diﬀerences between them.

5.1.2. Methodology for relating topics from diﬀerent data sources

In our experiment, we need to ﬁnd whether a topic from a dataset (e.g.,

Xamarin Forum) is also a topic fro m another da taset (e.g., Stack Overﬂow or

that one from Rosen and Shihab).

We related two to pics from diﬀerent datasets if they have: a) similarity on

their topic labels; or b) similar ity on the most signiﬁcant works that conform

the topic. The sig niﬁcant of a word is the probability g iven by the generated

LDA model to that word. For example, we related topics t

28 with t

xam

40 because they have the same topic label: “User Interface (Table)”. As the

labels do not always match, we related other topics using the words from the

topic. For example, topic t

8 was label as “Graphic and memory", and the

most similar topic in Xamarin that we found is t

xam

16, which was labeled as

“Video memory”. We related both topics because they sha res signiﬁcant words

like “memory” and “lea k”. The lists of topics (words and their probabilities) and

the related topics of each a re available in our appendix.

5.1.3. Methodology for ﬁltering most relevant questions from a topic

In this paper, we deﬁne relevant questions of a topic t as those questions

qs from t with: a) most number of views, or b) highest score, i.e., number of

up votes (only for Stack Overﬂow). Note that all questions we c onsider for

analyzing topic t have t as dominant topic. A dominant topic t of document d

is the most related topic (i.e., with highest probabilistic) according to the LDA

topic model generated.

The intuition is that if a question asks about a relevant subject or a recurrent

problem about Xamarin technology, it is frequently visited and appreciated with

up votes done by other developers. For each topic, we selected the questions

with at lea st 10,000 views and 10 up votes as score.

5.2. Results:

5.2.1. RQ 2: What are the main t opics discussed about Xamarin in Q&A sites?

Table 2 shows the topics from Stack Overﬂow and Xa marin Forum questions

discovered using the methodology described in section 5.1.1. The left-size dis-

plays the Stack O verﬂow topics and the right-side displays the Xama rin topics.

The column Id corres ponds to the topic identiﬁer assigned by Mallet; the col-

umn Label corresponds to the lab e l manually assigned by us using the method

presented in section 5.1.1. The topics are sor ted by decreasing NDDT. As ex-

plained by Linare s-Vasquez et al. [23] NDDT counts for each topic t the number

of documents that has as t as dominant topic. In our appendix we pr esented,

for each discovered topic, the words that compose the topic, their probabilities,

and NDDT metric. Let us ﬁrst present some of the discovery topics, and then

to compare the topics discovered from both da tasets.

Main Discussion Topics Discovered. Let us ﬁrst focus on Stack Overﬂow: the

top-4 topics (according with the number of dominant documents NDDT) are

related related to the view: t

11 and 32 both labelled with "Lis t (Forms)";

28 labelled with "User Interface (Tables)"; and t

23 " Use r Interface (Lay-

outs)". Then, the next two topics are not directly related to the user interface,

for example: t

22 "Emulator/Device/Simulator" and t

3 "Web Service".

For Xamarin Forum, the to p-5 topics from Xamarin Forum are related to

View or Controllers development: t

xam

7 and t

xam

10 both labelled with "View

Controllers/Navigation", t

xam

4 and t

xam

8 both labe lled with "Lists (Forms)",

and t

xam

3 la belled with "Forms (WebView)". Then, after them there are two

topics not related to the user interface: t

xam

1 "Resources/Files" and t

xam

"Android" (Activity).

When we analyzed the remaining topics, we observed tha t the topics dis-

cussed in the Q&A are diverse. For instance, those cover topics such as: re-

sources and ﬁles (t

6 and t

1), web services (t

3 and t

xam

37), langua ge

questions (t

9 and t

xam

33), databases (t

24 a nd topic

xam

30), notiﬁcations

Table 2: Main Topics discovered from Stack Overﬂow (Left) and Xamarin (right).

Stack Overﬂow Xamarin

Id Label Id Label

11,32 List (Forms) 7,10 View Controllers/Navigations

28 User Interface (Table) 4,8 Lists (Form s)

23 User Interface (Layout) 3 Forms (WebView)

22 Emulator/Device/Simulation 1 Resources/File

3 Web Services 5 Android (Activity)

5 Forms (XAML) 17 User Interface (Style)

1 Monodevelop/.net framework 11 Cross-Platform

30 View Controllers/Navigations 2 IDE/Licence

19 MVVM 19 Forms (XAML)

4 Library/Native 6 Map & Location

10 HTTP Request 28 IDE (Visual Studio)

7 Packages/Nuget/PCL 21 Social/APIs

21 Inputs (Event) 32 IDE (Simulator- for-Mac)

20 Android (Activity) 15 Application Store

39 User Interface (Style) 35 User Interface (Layout)

13 Library/Portability 18 Notiﬁcations

24 Databases 34 Emulator/Device/Simulation

8 Graphics/Memory 20 Library/Native

17 IDE 25 Inputs (Te xt)

9 Language Questions 26 Media/Images

18 Android (Debug/Device) 9 Error (Uniﬁed/Insight)

2 Excepti on/Error 12 Android (Version)

12 Phone Orient./Media-images 30 Databases

25 Error (Code/Compilation) 31 PCL/Library

6 Resources/File 14 Nuget/Package

29 Monodevelop 37 Web Services

35 Social/APIs 24 Inputs (Events)

27 File Operations 16 Video/Memory

26 Media/Images 13 Releases

16 Notiﬁcations 40 User Interface (Table)

15 User Interf.(Forms/WebView) 38 Connectivity

14 Media/Stre aming /Video 22 Testing

33 Lo cation 33 Language Questions (OOP)

31 Input (Text) 36 Phone Orientation/Media-images

34 Threading 27 Questions (Forms, Samp les)

36 Error Assembly 23 Excepti on

40 Binding/library 39 ErrorAssembly

38 W indows Platform 29 Error (Code/Compilation)

37 Testing

16 and t

xam

18), packages (t

7 a nd t

xam

31), architectural (t

19, t

xam

19), social (t

35 and t

xam

21), ma ps and locatio ns (t

33 and t

xam

6), IDEs

17 and t

xam

28).

Common Main Topics Stack Overﬂow and Xamarin Forum Q&A sites. We

observe that Xamarin Forum and Stack Overﬂow share 33 out of 40 (82.5%)

of the discovered topics. For instance, there are questions that discuss about

“Notiﬁcations”: in Stack Overﬂow those questio ns have as dominant topic t

and thos e from Xamarin Forum has as dominant topic t

xam

18. Seven topics

from Xamarin and other 7 from Stack Overﬂow were not related to any topic.

Main topics found from only one Q& A site. In bo th Stack Overﬂow and Xa-

marin Forum, there are 7 discovered main topics (12.5%) that we could not

manually related to any topic of the other Q&A site. For instance, we discov-

ered that one of the main to pic from Stack Overﬂow, t

34, is about “Thread-

ing”. However, we could not ﬁnd a ny topic between those from Xama rin that

discusses about threading. On the contrary, we discovered from the Xamarin

Forum site a topic (t

xam

15) which discusses about Application Store , but none

of the main topics from Stack Overﬂow is related to it. The lists of unrelated

topics are available in our appendix.

Respo nse to RQ 2: What are the main topics discussed about

Xamarin in Q&A sites? The top main topics discovered from Stack

Overﬂow and Xamarin forum discuss a bout User interfaces: Tables, Lay-

outs, Controllers, Forms. The 82.5% of the discovered main topics are

present in both Stack Overﬂow and Xamarin Forum sites.

5.2.2. RQ 3: How many main topics from Stack Overﬂow and Xamarin Forum

are also topics related to general mobile development discovered by Rosen

and Shihab?

As in this paper we have re plicated the study of Rosen and Shihab (which

fo c uses on general mobile development) over a Xamarin-related Q&A datasets,

we now proceed to compare the results (i.e., discovered topics) of both studies.

In this way, we are able to detect topics discovered from Xamarin Forum and

Stack Overﬂow that are: a) general, i.e., related to mobile but not particularly to

Xamarin technology, and b) closely r e lated to the development of c ross-platform

mobile applications using Xamarin.

Comparing topics from diﬀerent Q&A datasets. We compa red the topics previ-

ously discovered in section 5.2.1 with those related to mobile application devel-

opment presented by Rosen and Shihab [34]. As the authors a nalyzed questions

about three mo bile platforms (Android, iOS, and Windows Phone), we denom-

inated their topics as ‘general’, and we reference each as t

genmob

N, where N is

the id of the topic.

For comparing topics, we used the same manual method-

ology for matching topics presented in section 5.1.2. Note that, with the goal of

carrying out fa ir comparison, for discovering topics from a corpus of questions,

we used the same technique (LDA) and conﬁguration (values for alpha, beta, #

iterations and # topics) that Rosen and Shihab used in their work.

We found that 27 topics from Stack Overﬂow and 30 topics from Xamarin

Forum are re lated to, at least, one general topic from Rosen and Shihab. For

instance, topic t

35 is related to t

genmob

8 due to both share the same la bel:

“Social/APIs”. Other topics were also related by using the topics’ words instead

of their labe ls. Fo r instance, topic t

21 labeled as “Inputs (Event)” was related

to t

genmob

1 labele d as “Input” (label more general than the previous one),

due to both topics have almost the signiﬁcant words (i.e., those with higher

probability): ‘button’, ‘event’, ‘click’, ‘android’ and ‘keyboard’.

As the topics from [34] do not include any ‘id’, we consider that the ids of them correspond

to the row numbers of the table that presents the topics.

Respo nse to RQ 3: How many main to pics from Stack Overﬂow

and Xamarin Forum are also topics related to general mobile de-

velopment discovered by Rosen and Shihab? There are 27 and 30

topics discovered fr om Stack Overﬂow and Xamarin Forum (67.5% and

75%, resp.) that are also main topics in q uestion about mobile application.

The remaining topics, i.e., 13 (32.5%) and 10 (25%) topics from Stack Over-

ﬂow and Xamarin Forum, resp., are particularly related to cross-platform

app development using Xamarin.

This overlap between Xamarin and general topics makes sense since: a) Xa-

marin framework produces general c ode for diﬀerent platforms, which it could

be maintained during the app life-cycle in the same way as any ge neral app de-

veloped using traditional tools. b) a portion of a Xamarin application is usually

written in general language (Java for Android, Objective-C o r Swift for iOS)

rather than in the common language (Xamarin uses C# as common language).

for ex ample, the Evolve application for Android platform has the 90% of code

written in the C# whereas the remaining 10% in ge neral code.

. Thus, in

both cases, when writing or maintaining the portion of general code, a Xama rin

developers cold have the same kinds of questions than developers of general

apps. c) the general development of mobile apps includes the development of

cross-platforms mobile apps.

Now, let us to analyze those main topics that are not include betwe e n the

general topics, and those general main to pics that are not present between the

main topics discovered from Stack Overﬂow and Xamarin Forum.

Main topics from Stack Overﬂow and Xamarin Forum sites about Xamarin not

previously reported. Let us start discussing the discovered topics from Stack

Overﬂow and Xamarin Forum not reported by Rosen and Shihab. There are 13

and 10 discovered topics from Stack Overﬂow and Xama rin Forum, respe c tively,

that could not be related to any general topic. For instance, the to pic t

labeled as “MVVM” is one of them. As its label indicates, t

19 represents doc-

uments that discuss about the design pattern Model–view–viewmodel (MVVM),

which was introduced by Microsoft for facilitating the design of multi-tiers ap-

plication under the Microsoft’s platfor ms .NET. This pattern is recommend

by Xa marin documentation for implementing large a nd complex applications

on Xamarin platform.

Another topic is t

7 “Packages/Nuget/PCL” which

refers to concepts from the Microsoft technology. The ﬁrs t one is "Portable Class

Library (PCL)", which is a type of project in the .NET framework to write and

build portable .NET assemblies that are then referenced fr om, for example,

cross-platform apps.

The second concept is “Nuget”, a package manager for

https://github.com/xamarinhq/app-evolve

https://developer.xamarin.com/guides/xamarin-forms/enterprise-application-patterns/mvvm/

https://docs.microsoft.com/en-us/dotnet/standard/cross-platform/cross-platform-development-with-the-portable-class-library

.NET.

In summary, it makes sense to ﬁnd this topic only Xamarin-related

questions from Stack Overﬂow and Xamarin Forum: it covers questions about

reuse of functionality under the .NET platform during the development of cross-

platform mobile application using Xamarin framework. Similarly, in Xamarin

Forum we discovered two topics, each related to one mentioned concept: t

xam

31 “PCL/ L ibrary” and t

xam

“14 Nuget/Package”.

Furthermore, we also discovered topics from Stack Overﬂow and Xamarin

Forum that are not neither related to any general topics nor directly r elated to

Xamarin technology. Two of them are to pics t

37 and t

xam

22 both labeled as

“Testing”, which include words such as ‘uitest’, ‘testing’, ’unit’, ‘test’. Note that

no topic from Rosen and Shihab discuses about tes ting : the mentioned words

are not presented in any topic.

General topics not found in the Xamarin-related questions from Stack Overﬂow

and Xamarin Forum. Between the general mobile topics discovered by Rosen

and Shihab about g e neral mobile development, there are 9 out of 40 that are

not present in the main topics from Stack Overﬂow, whereas 10 are not related

to any from Xa marin Forum. 7 of them could not be related to any topic from

nether Stack Overﬂow nor Xa marin Forum. They a re: t

genmob

6 labelled with

“Phone/Sensors ”; t

genmob

12 “HTML5/Browser”; t

genmob

16 “App Distribution”;

genmob

19 “Processes/Activities”; t

genmob

20 “Data Structures”; t

genmob

24 “Data

Formatting”; and t

genmob

30 “Contacts”. For instance, topic t

genmob

6 includes

words that no discovered topic from Stack Overﬂow and Xamarin Forum ha s:

as ‘time’, ‘alarm’, ‘voice’, ‘speech’, ‘incoming’, ‘number’.

5.2.3. RQ 4: What are the most relevant quest ions from Xamarin-related top-

ics?

In section 5.2.2 we discovered topics that discuss abo ut Xamarin that were

not previously rep orted by Rosen and Shihab as main topics of general mobile

development. Now, we focus on three of those topics to know the ma in concerts

and pr oblematic asked by Xamarin developers. For each of them, we analyze

the mo st relevant comments, according to the methodology presented in Section

5.1.3.

MVVM (t

19). The MVVM (Model-View-ViewModel) is a pattern that helps

to separate the business and presentation logic of an applicatio n from its user

interface (UI). The pattern was intro duced by Microsoft for designing apps for

its diﬀerent platforms, including Xamarin, Windows Forms, WPF, Silverlight,

and Windows Phone.

The most relevant questions from topic MVVM are r e lated to Mvvmcross.

Mvvmcross is a framework built for ea sing the development of Xamarin fr ame-

works that proposes, for insta nce, an easier way to implement the MVVM pat-

https://www.nuget.org/

https://msdn.microsoft.com/en-us/library/hh848246.aspx

tern.

The question from Stack Overﬂow with highest score from topic MVVM

(25 upvotes) is about asynchronous programming: “How can I use async in an

MVVMCross view model?" (id:17187113)

. Between the answers, there are

two that solve the pr oblem: one (the accepted) proposes to use the language

keyword (async), the other proposes a solution that relies on the Mvvmcross

framework.

Other relevant questions about Mvvmcross focus on the communication be-

tween the pattern’s components, e.g., “Passing on variables from ViewModel to

another View [..]" (id:10192505), “MvvMCross bind command with parameter

[..]" (id:174927 42). Moreover, another relevant q uestion is about the diﬀerences

between Mvvmcross and ReactiveUI.

(ReactiveUI is a model-view-viewmodel

framework for a ll .NET platforms, including Xamarin).

User Interface (Forms/ViewList) (t

11). Xamarin.Form is an API of Xamarin

framework to build na tive apps for iOS, Android and Windows completely in

C# or in XML (using XAML language).

Xamarin.Forms pages represent

single screens within an app, and support layouts, buttons, labels, lists, and

other common controls. Each page and its controls are mapped to platform-

sp eciﬁc native user interface elements. Xamarin.Forms is bes t for developing

apps that require: a) little platform-speciﬁc functionality, or b) c ode s haring is

more important than cus tom UI.

The relevant questions from this topic t

11 are about Xamarin.Forms or its

components. For instance: “How to correctly use the Image Source property with

Xamarin.Forms?" (id: 30850510) is the most viewed question. Moreover, there

are relevant questions about the component ListView, e.g., “[..] ListView inside

StackLayout: How to set height?" (id: 24598 261) and “[..] untappable ListView

(remove selection ripple eﬀect)" (id: 35586243). The highest score q uestions

of topic t

11 are related to the IDE support of XAML development, such as

the code-completion (IntelliSense), e.g.: “Is it possible to u s e a Xaml designer or

intellisense with Xamarin.Forms?" (id: 2 4158201) (36 up votes). Other relevant

questions are also about XAML, e.g.: “[..] ListView ItemTapped/ItemSelected

Command Binding on XAML" (id: 24792991 ).

Library/Portability (t

13). The topic Library/Portability contains relevant

questions related to the architecture of Xamarin-based cross-platform apps.

Xamarin provides three alternative architectures that focus on sharing code

between cross-platform applications: 1) Shared Projects, 2) Portable Class Li-

braries (PCL), and 3) .NET Standard Libraries.

Relevant questions ask about these architectures, specially ab out the second

one. There are questions asking about clariﬁcation of those architectures, e.g.,

https://www.mvvmcross.com/

This number corresponds to the ID of a StackOverﬂow post. A post with id <ID> is

publicly available at https://stackoverﬂow.com/questions/<ID>

https://reactiveui.net/

https://www.xamarin.com/forms

https://docs.microsoft.com/fr-fr/xamarin/cross-platform/app-fundamentals/code-sharing

“What is a Portable Class Library?" (id: 5238955), “Portable Class Library vs.

library project" (id: 28746609), or questions about the diﬀerence of two architec-

tures, e.g., “Xamarin Shared Projects vs Portable class libraries" (id: 23990307).

Other relevant questions focus on problematic of using the PCL architecture, for

instance: “Unable to resolve assemblies that use Portable Class Libraries" (id:

13871267), or “Portable Class library and reﬂection" (id: 14061291). Finally,

the another group of relevant ques tions from this topic relates PCL and concur-

rency (threads): “Update UI thread from portable class library" (id: 14427340 ),

“Thread.Sleep() in a Portable Class Library" (id: 9251917).

6. Discussion

6.1. Threats to validity

6.1.1. Internal

Use of tags from posts. In sec tion 3 we applied a technique based on the use of

tags for retrieving posts related to Xamarin technology as done by Rosen and

Shihab [34]. T here is a threat when a develop er a) mislabels a post, i.e., tags

do not represent the real topic of the posts; or b) omits to label it. Moreover,

we used the titles from po sts to capture Xamarin-related posts that were not

labelled with Xa marin-related tags. A threat to validity is present when the title

does not represent the content of the post. To alleviate this threat we manually

analyzed a sample of the retrieved posts and veriﬁed the concordance betwe e n

the title and pos t’s content.

Representation of documents. We applied the LDA algorithm for modeling top-

ics. The input of LDA is a c orpus of document (See Section 5.1.1), where each

document contains information of a single post. We decided t o, as done by the

study we replicated, to only consider the title of the question due to, according

to them: 1) titles summarize and identify the main concepts being as ked in the

post, 2) the body of the question adds non-relevant information ra ther than

the main idea being asked about, and 3) we are interested in what issues the

developers are asking about and adding the answer posts would not make sense

[34].

Conﬁguration of LDA. LDA needs 4 conﬁguration arguments (alpha, beta,

number of topics and number iterations). Choosing optimal values for those

arguments is a diﬃcult task, so, to alleviate this threat, as done by [17, 23, 34],

we tried diﬀerent conﬁgurations to choose, to our best judgment, the bes t con-

ﬁguration. The selection criteria used by those works were: a) inspection at

the average dominant topic probabilities given by the resulting model [34], and

b) assurance that topics do not have much overlap in top terms, are not copies

of each other, and are not share excessive disjoint concepts or ideas [17]. In our

experiment we decided to use the same conﬁguration that the study we repli-

cated from Rosen a nd Shihab. Reusing the conﬁguration allowed us to compare

the topics discovered fro m Xamarin-r elated questions against those by Rosen

and Shihab fr om mo bile-related questio ns .

Label of discovered topics. As do ne by the mentioned related works (e.g., [34,

23]), we manually analyzed the results produced by LDA for labeling each topic

with a human readable label, based on a set of words from the topic and their

probabilistic. To the bes t of our knowledge, there is no tool for automatica lly

labeling topics. To alleviate the threat of mislab e ling topics or mismatching

of topics from diﬀerent sources, we have carried out those task s using a pe e r-

reviewed process and the results are publicly available.

6.1.2. External

One potential threat is that sources of information used for studying Q&A

related to Xamarin technology are not representative. To mitigate that threat

we selected two so urces: Stack Overﬂow and Xamarin Forum. The former is

one of the most popular and used Q&A site by software developers and latter

is the oﬃcial forum of the Xamarin technolog y.

6.2. Future Work

For future work, we plan to continue exploring the two data sets of Xamarin-

related questions. Future research direction could focus on:

6.2.1. Combine additional sources of information

By inspecting the relevant questions of this topic, we notice that many o f

their accepted answers include a link to the oﬃcia l Xamarin doc umentation

web site. For instance, the mentioned most viewed post (id: 30850510) has an

accepted answers tha t cites a page from the oﬃcial documentation as source

of its response. That ﬁnding triggers some research questions for future work:

a) How many posts from Stack Overﬂow link to the oﬃcial documentation in

their questions/answers?, b) How much do (Xamarin) developers ask questions

which solution ar e already included in the documentation?. Moreover, we also

observe that answers on Stack Overﬂow a lso include links to the Xamarin Forum,

the oﬃcial Q&A site of Xamarin. For e xample, the question id 24598261 from

Stack Overﬂow has an accepted answer based on a post from the Xamarin

Forum (id: 66248).

Other paper s have focused on combining diﬀerent sources

of information (e.g ., [46, 21, 42, 45, 41]). However, to our knowledge, nobody

has linked questions from two Q&A sites nor focused on Xamarin source of

information.

6.2.2. Study the architecture of cross-platform mobile apps

As we dis c ussed on Section 5.2.3, relevant ques tions are about mobile apps

architectures and frameworks. Future work can study and compa re apps de-

veloped using diﬀerent architectures. For instance, a research could focus on

analyzing which is the best o ptio n between the architectures Shared Projects

and Portable class libraries in term o f, for instance , the expertise the develop-

ers needs to develop and maintain apps with tho se architectures, or the ease

https://forums.xamarin.com/discussion/comment/66248

of evolving an application according to the upgrade of the mobile platforms.

Moreover, another possible resear ch for future work could study the beneﬁces

and disadvantag e s of developing and ma intaining cross-platforms apps that used

this frameworks (such as Mvvmcross) w.r.t. apps developed without them i.e.,

using only the Xa marin framework.

7. Conclusion

Cross-compiler mobile development frameworks allow mobile developers to

create native cross-platform mobile applications with the pr omise of simplify-

ing the development and maintenance phases by reusing code so urce across the

diﬀerent platforms. To study and characterize the development a nd mainte-

nance of cros s-platforms apps using cross-compiler frameworks, in this paper

we present two datasets with questions and answers (Q&A): one with Q&A

from the oﬃcial Xamarin Forum, the other with Xamarin-related Q&A from

Stack Overﬂow. We then use them in a replication study of [34] for discover-

ing the main discussion topics from questions related to Xamarin technology.

We compared the discovered topics ag ainst those main topics related to mobile

development discovered by [34]. We found that a portion of the topics from

the Xamarin-rela ted questions were not previous ly identiﬁed when discussing

about general mobile applications. To promote more studies about Xamarin

and cross-platform mobile frameworks, the two Xamarin-related Q&A datasets

are publicly available.

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