Question

I am writing a small game for Android. The game is drawn on a SurfaceView using a Thread. Within the run() method of the Thread, I test to see if the game is over and if it is, I try to display the game over dialog however that gives me the forementioned error message.
I know that this error occurs when a non-UI thread tries to mess with the UI. What I’d like to know is the best approach to displaying such a dialog. I’ve pasted the code below.
Thanks for your help:

public class BouncingBallActivity extends Activity{

    private static final int DIALOG_GAMEOVER_ID = 0;
    private BouncingBallView bouncingBallView;

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        bouncingBallView = new BouncingBallView(this);
        bouncingBallView.resume();
        setContentView(bouncingBallView);
    }

    protected Dialog onCreateDialog(int id)
    {
        switch (id) {
        case DIALOG_GAMEOVER_ID:
            AlertDialog.Builder builder = new AlertDialog.Builder(this);
            builder.setMessage("Game Over.")
                    .setCancelable(false)
                    .setPositiveButton("Try Again",
                            new DialogInterface.OnClickListener()
                                {

                                public void onClick(DialogInterface arg0,
                                        int arg1)
                                {
                                    bouncingBallView.resume();

                                }
                            })
                    .setNegativeButton("Exit",
                            new DialogInterface.OnClickListener() {

                                public void onClick(DialogInterface dialog,
                                        int which)
                                {
                                    BouncingBallActivity.this.finish();

                                }
                            });

            AlertDialog gameOverDialog = builder.create();
            return gameOverDialog;
        default:
            return null;
        }


    }


    class BouncingBallView extends SurfaceView implements Runnable
    {
        SurfaceHolder   surfaceViewHolder;
        Canvas          canvas;
        Context         context;
        Thread          drawingThread;

        boolean         drawingThreadIsRunning;
        boolean         isInitialised;

        Ball            ball;
        ArtificialIntelligence ai;

        BouncingBallView(Context context)
        {
            //
        }

        public void pause()
        {
            isInitialised = false;
            drawingThreadIsRunning = false;
            boolean joiningWasSuccessful = false;

            while(!joiningWasSuccessful)
            try {
                drawingThread.join();
                joiningWasSuccessful = true;
            } catch (InterruptedException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }

        }

        public void resume()
        {
            isInitialised = false;
            drawingThread = new Thread(this);

            drawingThread.setName("Drawing Thread");
            drawingThreadIsRunning = true;
            drawingThread.start();

        }

        public void run()
        {
            while(drawingThreadIsRunning)
            {
                if(!surfaceViewHolder.getSurface().isValid())
                    continue;

                if(gameOver())
                    BouncingBallActivity.this.showDialog(DIALOG_GAMEOVER_ID);

                try{
                    canvas = surfaceViewHolder.lockCanvas();
                    if(!isInitialised)init(canvas);
                    update();
                    surfaceViewHolder.unlockCanvasAndPost(canvas);
                }catch(Exception e)
                {
                    Log.e(BouncingBallActivity.this.toString(),String.format("%s: Just as the emperor had foreseen!\n(This error is expected. Canvas destroyed while animations continue.)", e.toString()));
                }
            }
        }

        private void init(Canvas canvas)
        {
            ball = new Ball(canvas, Color.GREEN);
            ai   = new ArtificialIntelligence(canvas, (int) (ball.getX()+100),canvas.getWidth());

            isInitialised = true;
        }

    }
}

Answer 1

Try like this… you cannot make any changes to ui from other than main thread..put this part inside your thread after if(gameOver())

//if(gameOver())
 runOnUiThread(new Runnable() {
           @Override
           public void run() {

               BouncingBallActivity.this.showDialog(DIALOG_GAMEOVER_ID);
           }
       });