Problem with View Invalidate() and Handler

i'm trying to fix this problem for more than 2 days now and have become quite desperate.

I want to write a 'Checkers-like' board game for android. The game engine itself is kinda complete but i have problems with updating the views.

I wrote a little example class to demonstrate my problem:

public class GameEngineView extends View {

private static final String TAG = GameEngineView.class.getSimpleName();

private int px;
private int py;
private int cx;
private int cy;

private boolean players_move;
private int clickx;
private int clicky;

Random rgen;

private RefreshHandler mRedrawHandler = new RefreshHandler();

class RefreshHandler extends Handler {
    @Override
    public void handleMessage(Message msg) {            
        GameEngineView.this.update();
        GameEngineView.this.invalidate();
        Log.d(TAG, "invalidate()");            
    }

    public void sleep(long delayMillis) {
        this.removeMessages(0);
        sendMessageDelayed(obtainMessage(0), delayMillis);
    }
};

public GameEngineView(Context context) {
    super(context);
    setFocusable(true);
    players_move = true;
    rgen = new Random();
}

public void 开发者_开发百科update() {
    updateGame();
    Log.d(TAG, "update -> sleep handler");
    mRedrawHandler.sleep(100);
}

public void updateGame() {
    if(players_move) {
        px = clickx;
        py = clicky;
    } else {
        calcAIMove();
        switchMove();
    }        
}

public void switchMove() {
    players_move = !players_move;
}

public void calcAIMove() {
    for(int i = 0; i < 20000; i++) {
        cx = rgen.nextInt(getWidth());
        cy = rgen.nextInt(getHeight());
    }
}

@Override
public boolean onTouchEvent(MotionEvent event) {
    Log.d(TAG, "event");
    int eventaction = event.getAction();
    if(eventaction == MotionEvent.ACTION_DOWN) {
        Log.d(TAG, "action_down");
        clickx = (int) event.getX();
        clicky = (int) event.getY();
        switchMove();
        update();
    }
    return super.onTouchEvent(event);
}

@Override
public void onDraw(Canvas canvas) {
    super.onDraw(canvas);
    Paint green = new Paint();
    green.setColor(Color.GREEN);
    Paint red = new Paint();
    red.setColor(Color.RED);
    canvas.drawColor(Color.BLACK);
    canvas.drawCircle(px, py, 25, green);
    canvas.drawCircle(cx, cy, 25, red);
}

}

The function calcAIMove() just burns time to simulate a real evaluation of the position in a board game.

Now my Problem is: If the player clicks(makes a move) the green ball is first drawn when the ai move calculation has been complete. So both moves are drawn at the same time.

I wonder HOW to accomplish this: -Player clicks -green Ball is drawn -AI calculates -red ball is drawn -and so on..

When searching the web i found a lot of game loop examples but they all need a Thread with constant polling.. it should be possible without this since the whole program runs sequentially .. right?

Hoping for advice.

thanks, Dave

Here is how your game could work:

1. user makes a move
2. game view is updated
3. game switches to CPU's turn
4. sleep to simulate CPU player thinking (if move computation is trivial)
5. compute CPU's move
6. game view is updated
7. game switches to player's turn

There is no need for constant polling in a turn-based game like this. The only place you should have sleep is in step 4, so you can remove it from the other areas (no need for the old update() method which is just a delayed call to updateGame()).

One way to implement this is to simply delay the call to calcAIMove() and switchMove() by putting it into a Runnable and using Handler.postDelayed() or similar.

I don't see how you are disabling touch events when it is the CPU's turn, which can lead to a host of other problems if switchMove() and update() are still being called...

In your game loop you can use a instance of TimerTask to ensure certain delay between greenBall and some other drawing task. Game tutorials like Snake and LunarLander are great references on when and if you need to invalidate your View. Hope this helps a little!

ok so the answer provided by antonyt helped me solve this.. I provide the corrected code for other interested ones.

public class GameEngineView extends View {

private static final String TAG = GameEngineView.class.getSimpleName();

private int px;
private int py;
private int cx;
private int cy;

private boolean players_move;
private int clickx;
private int clicky;

Random rgen;

/**
 * Create a simple handler that we can use to cause animation to happen.  We
 * set ourselves as a target and we can use the sleep()
 * function to cause an update/invalidate to occur at a later date.
 */
private RefreshHandler mRedrawHandler = new RefreshHandler();

class RefreshHandler extends Handler {
    @Override
    public void handleMessage(Message msg) {
        GameEngineView.this.update();
    }

    public void sleep(long delayMillis) {
        this.removeMessages(0);
        sendMessageDelayed(obtainMessage(0), delayMillis);
    }
};

public GameEngineView(Context context) {
    super(context);
    setFocusable(true);
    players_move = true;
    rgen = new Random();
}

public void update() {
    if(players_move) {
        Log.d(TAG, "new player x");
        px = clickx;
        py = clicky;
        GameEngineView.this.invalidate();
        switchMove();
        mRedrawHandler.sleep(100);
    } else {
        Log.d(TAG, "new ai x");
        calcAIMove();
        GameEngineView.this.invalidate();
        switchMove();            
    }

    Log.d(TAG, "update -> sleep handler");        
}


public void switchMove() {
    players_move = !players_move;
}

public void calcAIMove() {
    for(int i = 0; i < 100000; i++) {
        cx = rgen.nextInt(getWidth());
        cy = rgen.nextInt(getHeight());
    }
}

@Override
public boolean onTouchEvent(MotionEvent event) {
    Log.d(TAG, "event");
    int eventaction = event.getAction();
    if(players_move && eventaction == MotionEvent.ACTION_DOWN) {
        Log.d(TAG, "action_down");
        clickx = (int) event.getX();
        clicky = (int) event.getY();
        update();
    }
    return super.onTouchEvent(event);
}

@Override
public void onDraw(Canvas canvas) {
    super.onDraw(canvas);
    canvas.drawColor(Color.BLACK);
    Paint green = new Paint();
    green.setColor(Color.GREEN);
    Paint red = new Paint();
    red.setColor(Color.RED);

    canvas.drawCircle(px, py, 25, green);
    canvas.drawCircle(cx, cy, 25, red);
}

}