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About Stef Epardaud

Stef Epardaud
Stéphane Épardaud is a long-time open source user and contributor, now working on the Ceylon compiler because if you're not writing a compiler you're not doing proper programming ;)

Ceylon on mobile devices

Ceylon already runs on the JVM, whether bare-bones, via JBoss Modules, Vert.x, Java EE Servlet containers such as WildFly, or OSGi containers, as well as on JavaScript VMs such as Node.js and the browser. But today we’re going to explain how to run Ceylon on mobile devices, not just in the browser (though it does play a part in it), but as applications, via Apache Cordova.

Apache Cordova allows you to write applications for every mobile platform, including Android and iOS, using nothing but HTML, CSS and JavaScript. Since Ceylon compiles to JavaScript this is perfect as it allows us to run our Ceylon applications on iOS, via the JavaScript compiler backend.

Note that this article is using Ceylon 1.2.3 which is not yet released, because the JavaScript runtime in Cordova on Android had one peculiarity we had to work around in the language module JavaScript implementation. Luckily you can get nightly builds of Ceylon 1.2.3 and the Ceylon 1.2.3 SDK.

Writing your Ceylon Cordova application

Installing Apache Cordova

First, install Apache Cordova and add two platforms. I haven’t been able to test the iOS platform since it requires an OSX platform to build and an iOS device to test, and I lack both, so I will explain how to package for Android and the browser, and let you guys try it out for iOS, but I have enough faith in Apache Cordova that it will Just Work™.

# Install npm, the Node.js package manager
$ sudo apt-get install npm
# Then install Apache Cordova
$ npm install cordova

Small note: for me this installed things in ./node_modules/cordova and the Apache Cordova command in ./node_modules/cordova/bin/cordova, so adapt your path as you must.

# Create your application
$ cordova create ceylon-cordova-demo
$ cd ceylon-cordova-demo
# Now add the browser and Android platforms
$ cordova platform add browser
$ cordova platform add android

At this point you have your application ready to be checked in your browser:

$ cordova platform run browser

Or in an Android emulator, provided you have downloaded the Android SDK already:

$ ANDROID_HOME=.../Android/Sdk cordova platform build android
$ ANDROID_HOME=.../Android/Sdk cordova platform run android

Getting a little side-tracked about styling

Writing an application using just HTML and CSS means you have to make some effort for it to look good, and instead I decided to delegate to usePolymer so that my application would have the look and feel of Android Material Design applications to feel even more like a native application on Android. No doubt a similar look and feel exists for iOS.
So let’s download Polymer in our application’s HTML sources:

$ npm install bower
$ cd www
$ bower init
# At this point just hit enter/Yes/No until it's set up 
$ bower install --save Polymer/polymer
$ bower install --save Polymerelements/paper-item

And now edit www/index.html to use Polymer:

<script src="bower_components/webcomponentsjs/webcomponents.js"></script>
<link rel="import" href="bower_components/paper-item/paper-item.html">
<link rel="import" href="bower_components/paper-item/paper-item-body.html">

You should also remove the default CSS:

<link rel="stylesheet" type="text/css" href="css/index.css">

Getting require.js and jQuery

Ceylon compiles to JavaScript modules by way of require.js, so we’re going to have to download it too:

$ cd www/js
$ wget http://requirejs.org/docs/release/2.2.0/minified/require.js

Our Ceylon demo will use jQuery to add elements to the HTML page, so we also need it:

$ cd www
$ bower install --save jquery

Now edit www/index.html to use both:

<script type="text/javascript" src="js/require.js"></script>
<script src="bower_components/jquery/dist/jquery.js"></script>

Writing the Ceylon application

We’re going to write a trivial application that queries Ceylon Herd for the list of modules, to display them in a list.
Let’s start by creating a Ceylon module in source/cordova/demo/module.ceylon:

module cordova.demo "1.0.0" {
    import ceylon.json "1.2.3";
}

And our application’s main method in source/cordova/demo/run.ceylon:

import ceylon.json { parseJson = parse, JsonObject = Object, JsonArray = Array }

shared void run() {
    dynamic {
        // The HTML element where we'll add our items
        dynamic target = jQuery("#target");
        // The function called when we get data from the server
        void success(dynamic data){
            // Parse the JSON
            assert(is JsonObject json = parseJson(data),
                   is JsonArray results = json["results"]);
            // Iterate modules
            for(res in results){
              assert(is JsonObject res);
              // Get the list of versions
              assert(is String name = res["module"],
                     is JsonArray versions = res["versions"]);
              // Join them
              value versionText = ", ".join(versions.narrow<String>());
              // Now add the HTML items
              dynamic item = jQuery("<paper-item/>");
              dynamic body = jQuery("<paper-item-body two-line/>").appendTo(item);
              jQuery("<div/>").text(name).appendTo(body);
              jQuery("<div secondary/>").text(versionText).appendTo(body);
              target.append(item);
            }
        }
        // Query Herd for the list of modules
        jQuery.get("https://modules.ceylon-lang.org/api/1/complete-modules?module=ceylon.", null, success, "text");
    }
}

<Now, obviously using jQuery to add HTML is far from ideal, so I can’t wait for someone to extend ceylon.html to allow Polymer web components!
We can now compile our application for JavaScript:

$ ceylon compile-js

And copy our compiled module and all its dependencies to where the Apache Cordova application will find them in www/modules:

$ ceylon copy --with-dependencies --js --out www/modules cordova.demo/1.0.0

Invoking the Ceylon module from the Cordova application

Because we’re going to use require.js inline and connect to Ceylon Herd, we have to adjust the Apache Cordova permissions in www/index.html, so find that line and edit it as such:

<meta http-equiv="Content-Security-Policy" 
      content="default-src 'self' 'unsafe-inline' 
               https://fonts.googleapis.com
               https://fonts.gstatic.com;
               connect-src *">

We’re left with just invoking our Ceylon function in www/index.html:

<script type="text/javascript">
  // tell require.js where our Ceylon modules are 
  require.config({
    baseUrl:'modules',
  });
  // when the document is ready
  jQuery(function(){
    // load our Ceylon module
    require(['cordova/demo/1.0.0/cordova.demo-1.0.0'], function(client) {
      // and call our run method
      client.run();
    });
});
</script>

And setting up the target HTML elements where we’re going to add every loaded module (in the same file):

<body id="app" unresolved>
  <app-shell class="fit">
    <div id="target" role="listbox"></div>
  </app-shell>
</body>

Trying it

And that’s it, try it out in your browser:

$ cordova platform run browser

Or in an Android emulator:

$ ANDROID_HOME=.../Android/Sdk cordova platform build android
$ ANDROID_HOME=.../Android/Sdk cordova platform run android

If you have OSX and iOS dev tools, please try this with the iOS Cordova platform and let me know how it works :)

In the future, we would benefit from having a type-safe API in front of the Cordova JavaScript API that lets you access native mobile APIs such as the camera, GPS, contacts, but even without it you can already use them using dynamic blocks.

And now for the teaser… this is only one method to run Ceylon on Android, because obviously it may be more desirable to use the JVM compiler backend and integrate with the Android Tools to run Ceylon on Android using only type-safe APIs. Don’t worry, it’s coming, and next week I will show you how :)

Reference: Ceylon on mobile devices from our JCG partner Gavin King at the Ceylon Team blog blog.

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