Regaining focus to main activity after making a call from phonegap

android, cordova

Solution

I managed to solve this one after many hours of hacking. It seems, that once a new android task takes control, which is what happens when the built-in dialer is used to make a call, the background task started from the task which made the call also loses its privilege to start new activities, unless it is starting the activity in a new task.

This means, that is an AsyncTask is started from the activity before making the call, then sleeping a bit to make sure the dialer task/activity is open, it must start a new task to gain back focus. It is not an option to start the Cordova activity again, as that would effectively restart the entire app, so the solution is to make a thin restart task, that finished immediately.

In the Cordova plugin, the following inner class can be placed:

protected class RestartTask extends AsyncTask<Void, Void, Void>{
    protected RestartTask() { }

    @Override
    protected Void doInBackground(Void... unused){
        try {
            // pass time so the built-in dialer app can make the call
            Thread.sleep(MyPlugin.restartDelay);
        }
        catch (InterruptedException localInterruptedException)
        {
            Log.d("MyPlugin", "RestartTask received an InterruptedException");
        }

        return null;
    }

    @Override
    protected void onPostExecute(Void justEyeCandy){
        super.onPostExecute(justEyeCandy);

        // Start the RestartActivity in a new task. This will snap the phone out of the built-in dialer app, which
        // has started in it's own task at this point in time. The RestartActivity gains control and finishes
        // immediately, leading control back to the activity at the top of the stack in the
        // app (where the user came from when making the call).
        Intent restartIntent = new Intent(MyPlugin.this.ctx.getApplicationContext(), RestartActivity.class);
        restartIntent.setFlags(Intent.FLAG_ACTIVITY_NEW_TASK);
        MyPlugin.this.ctx.getApplicationContext().startActivity(restartIntent);
    }
}

This `AsyncTask` can be fired up in the plugin by calling:

this.ctx.runOnUiThread(new Runnable(){
    public void run(){
        try {
            RestartTask restartTask = new RestartTask();
            restartTask.execute();
        }
        catch (Exception e) {
            Log.d("MyPlugin", "Exploded when trying to start background task: " + e.getMessage());
        }
    }
});

The class the AsyncTask starts in a new task is then:

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

        // the prototype RestartActivity there is a possibility that this will be the root activity of the app.
        // If that is the case, this activity will boot the main activity of the app in a new task, before signing off.
        // However, this is not the case for this app, as restarts are only used once a call diversion has taken place,
        // form within the app.
        if (isTaskRoot())
        {
            // Start the app before finishing
            String packageName = this.getBaseContext().getPackageName();
            Intent startAppIntent = this.getBaseContext().getPackageManager().getLaunchIntentForPackage(packageName);
            startAppIntent.addFlags(Intent.FLAG_ACTIVITY_PREVIOUS_IS_TOP);
            startActivity(startAppIntent);
        }

        // Now finish, which will drop the user in to the activity that was at the top of the task stack
        finish();
    }
}

Problem

Original source