JavaScript (Rhino) on Android

Finally I have found a great dynamic language for writing Android apps - Rhino, a JavaScript implementation in Java. Rhino can run in interpreted mode, which makes it suitable for running on Dalvik (since on-the-fly byte code generation on Dalvik isn't implemented by dynamic languages, yet).

I used the work by Brice Lambson as a starting point. He has created a version of Rhino for the Android Scripting Environment (ASE). With the new release of the ASE you can now write scripts using JavaScript.

Since I want to write applications for Android in a dynamic language, I decided to experiment with embedding Rhino in an Android app. I created a new Android Java project, grabbed the Rhino jar-file from the ASE web site and dropped it in the libs directory. By browsing the documentation at the Rhino web site, it was quite straightforward to write a working demo.

Here is the code:

package miki.jsapp;

import android.app.Activity;
import android.os.Bundle;

import org.mozilla.javascript.*;

public class JSApp extends Activity
{
    @Override
    public void onCreate(Bundle savedInstanceState)
    {
        super.onCreate(savedInstanceState);

        doit(
             "var widgets = Packages.android.widget;\n" +
             "var view = new widgets.TextView(TheActivity);\n" +
             "TheActivity.setContentView(view);\n" +
             "var text = 'Hello Android!\\nThis is JavaScript in action!';\n" +
             "view.append(text);"
             );
    }
   
    void doit(String code)
    {
        // Create an execution environment.
        Context cx = Context.enter();

        // Turn compilation off.
        cx.setOptimizationLevel(-1);

        try
        {
            // Initialize a variable scope with bindnings for 
            // standard objects (Object, Function, etc.)
            Scriptable scope = cx.initStandardObjects();

            // Set a global variable that holds the activity instance.
            ScriptableObject.putProperty(
                scope, "TheActivity", Context.javaToJS(this, scope));

            // Evaluate the script.
            cx.evaluateString(scope, code, "doit:", 1, null);           
        }
        finally
        {
            Context.exit();
        }
    }   
}