# Using Eclipse Xtext to Simplify Mobile Application Development

| by Jean-Jacques Dubray 3 Followers on Aug 10, 2010. Estimated reading time: 3 minutes |

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Daniel Schneller wrote an introduction on Xtext by creating a grammar that provides:

an easy to use and reliable way for configuring navigation through mobile Java applications

In the past, his team hard-coded the application's navigation paths, but because of the growing complexity of the applications, they needed a new solution:

First we thought about an XML based configuration, but this seemed to be a hassle to write (and read) and also would mean we would have to pay the price of parsing it on every application startup.

Recently, they stumbled upon Eclipse Xtext:

[Xtext is] an Eclipse based framework/library for building text based DSLs.
In short, you just provide a grammar description of a new DSL to suit your needs and with – literally – just a few mouse clicks you are provided with a content-assist, syntax-highlight, outline-view-enabled Eclipse editor and optionally a code generator based on that language.

Xtext was originally developed by Sven Efftinge as part of openArchitectureWare and became an integral part of Eclipse this year. It is based on EMF (Eclipse Modeling Framework) and ANTLR.

navigation rules for MyApplicationmappings { map permission AdminPermission to "privAdmin" map permission DataAccessPermission to "privData" map coordinate Login to "com.danielschneller.myapp.gui.login.LoginController"                        in "com.danielschneller.myapp.login" map coordinate LoginFailed to "com.danielschneller.myapp.gui.login.LoginFailedController"                              in "com.danielschneller.myapp.login"  map coordinate MainMenu to "com.danielschneller.myapp.gui.menu.MainMenuController"                           in "com.danielschneller.myapp.menu" map coordinate UserAdministration to "com.danielschneller.myapp.gui.admin.UserAdminController"                                     in "com.danielschneller.myapp.admin" map coordinate DataLookup to "com.danielschneller.myapp.gui.lookup.LookupController"                             in "com.danielschneller.myapp.lookup"}navigations { define navigation USER_LOGON_FAILED define navigation USER_LOGON_SUCCESS define navigation OK define navigation BACK define navigation ADMIN define navigation DATA_LOOKUP}navrules { from Login  on navigation USER_LOGON_FAILED   go to LoginFailed  on navigation USER_LOGON_SUCCESS   go to MainMenu from LoginFailed  on navigation OK   go to Login from MainMenu  on navigation ADMIN   go to UserAdministration   with AdminPermission  on navigation DATA_LOOKUP   go to DataLookup   with DataAccessPermission   from UserAdministration  on navigation BACK   go to MainMenu from DataLookup  on navigation BACK   go to MainMenu}

Xtext lets you define both the syntax and the metamodel behind your grammar at the same time. From there, Xtext generates the code of an Eclipse plugin that will allow developers to create metadata:

The generated editor comes complete with intellisense, color coding, syntax error detection and even the ability to detect broken references, across multiple metadata files.

Xpand was then used to parse and translate the grammar into a HashMap-based data structure:

public class NaviRules {    private Map navigationRules = new Hashtable();    // ...     public NaviRules() {        NaviDestination naviDest;        naviDest = new NaviDestination();        naviDest.action = "USER_LOGON_FAILED";        naviDest.targetClassname = "com.danielschneller.myapp.gui.login.LoginFailedController";        naviDest.targetBundleId = "com.danielschneller.myapp.login";                store("com.danielschneller.myapp.gui.login.LoginController", naviDest);                naviDest = new NaviDestination();        naviDest.action = "USER_LOGON_SUCCESS";        naviDest.targetClassname = "com.danielschneller.myapp.gui.menu.MainMenuController";        naviDest.targetBundleId = "com.danielschneller.myapp.menu";                store("com.danielschneller.myapp.gui.login.LoginController", naviDest);          // =============================================================================                naviDest = new NaviDestination();        naviDest.action = "OK";        naviDest.targetClassname = "com.danielschneller.myapp.gui.login.LoginController";        naviDest.targetBundleId = "com.danielschneller.myapp.login";                store("com.danielschneller.myapp.gui.login.LoginFailedController", naviDest);                // .... and so on ...    }}


Daniel sees several advantages over XML for mobile applications:

No XML parsing necessary on application startup, saving some performance
Validation of the navigation rules ahead of time, preventing parse errors at runtime
No libraries needed to access the information – by putting everything in a simple HashMap we do not have to rely on any non-standard classes whatsoever

Textual DSLs are maturing rapidly and finding a broad range of applicable scenarios on different platforms. Did you already use a textual-DSL in a real world scenario? What for? What is your feedback?

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what kind of mobile platform it support?

I am interested in this concept, but what kind of platform it support right now?
iPhone, android, j2ME. It seems the DSL generates the java code.

Re: what kind of mobile platform it support?

Steve:

Xtext / Xpand is actually a framework from which you can generate any artefact you want (code, config files, documentation...). I successfully built an Objective-C code generator with it.

I found Daniel's article interesting because it shows how easy it is do that by providing an end-to-end scenario.

Nice

Jean,

thanks for the article on Xtext. It's always good to see how people use the technologies and frameworks, that I helped to develop.

Just one remark: The Xtext prototype which was part of the openArchitectureWare project was developed by Sven Efftinge [1]. When Xtext became a project at Eclipse it was completely rewritten by a team of great guys around Sven [2]. It's us, who share the vision about Xtext and its future.

Regards,
Sebastian

[1] blog.efftinge.de/
[2] www.eclipse.org/projects/project_summary.php?pr...

Re: Nice

Sorry about that, I was under the impression that Markus was behind it. I appreciate the clarification and I apologize for not looking into it further. I'll correct the article.
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