Re: Ada 'hello world' for Android; success!

[Jeffrey Creem <jeff@thecreems.com>]

On 10/26/2011 9:18 PM, Stephen Leake wrote:
> I've managed to get an Ada 'hello world' working on Android. It follows
> the example at
> http://developer.android.com/resources/tutorials/hello-world.html
> translated to Ada.
>
> Here's the Ada 'main program':
>
> with Android.App.Activity;
> with Android.OS.Bundle;
> package Hello is
>
>     --<Ada package>$<Ada type>  must match ../AndroidManifest.xml manifest | application | activity | android:name
>     type Typ is new Android.App.Activity.Typ with null record;
>
>     overriding procedure OnCreate
>       (This               : access Typ;
>        savedInstanceState : access Standard.Android.Os.Bundle.Typ'Class);
>     pragma Export (Java, OnCreate, "onCreate");
>
> end Hello;
> --  Prefix must match ../AndroidManifest.xml manifest | package
> pragma Export (Java, Hello, "net.example.helloada.hello");
>
> package body Hello is
>
>     overriding procedure OnCreate
>       (This               : access Typ;
>        savedInstanceState : access Standard.Android.Os.Bundle.Typ'class)
>     is
>        type Super_Ref is access all Android.App.Activity.Typ;
>     begin
>        Android.App.Activity.Oncreate (Super_Ref (This), savedInstanceState);
>
>        --  FIXME: use R.layout
>        --
>        --  need to run jvm2ada on ../gen/net/example/R.java, but that's
>        --  generated by the ant process that runs after this code is
>        --  compiled, so we have to learn how to break that up or
>        --  something.
>        --
>        --  until then, get this constant from R.java (value for 'layout')
>        Android.App.Activity.SetContentView (Android.App.Activity.Ref (This), 16#7f030000#);
>     end OnCreate;
>
> end Hello;
>
> It runs on the Android emulator provided with the Android SDK, and on my
> HTC Inspire.
>
> As you can see, there are still some rough edges in the build process. I
> could have hard-coded the 'hello' string here, but that's not what the
> Java program does; this demonstrates that the Ada code really is using
> all the Java GUI resources and classes properly.
>
> Mostly I didn't want to spend any more time figuring out how to
> customize the Android SDK build tools. They work really nicely if you
> are doing simple Java stuff, but really get in the way when you want to
> do something more complicated.
>
> I started with GNAT GPL 2011, jvm target. I had to fix two bugs in
> jvm2ada, one bug in the jvm-gnat backend (all reported to AdaCore with
> patches), and work around another bug in the gnat front end (also
> reported to AdaCore). Not too bad :).
>
> Any suggestions for where to post more info?
> wikibooks.org/wiki/Ada_Programming looks like a good place, but I'm not
> sure where this fits in that hierarchy.
>
> I can post a .tar.gz (or just the .apk :) on my own website if anyone is
> interested in getting a quick look now.
>
> There are some interesting issues in the Ada<->  Java mapping; for
> example, Ada packages map to Java nested classes, so you have to put the
> desired Java package name in the 'pragma Export' external name.
>
> Figuring out how to tell the SDK build tools exactly what was going on
> was the most frustrating; the documentation on those is totally
> inadequate. I managed to find some answers in the source code for the
> tools; at least it is all open source.
>
> Fixing the bugs in the GNAT tools was easy by comparison, once I had
> test cases.
>
> Now I can work on my music player app, and get away from Java ;).
>

Perhaps a new sourceforge project, or get it posted into the existing 
GNU Ada project?