efficient android rendering

I've read quite a few tutorials on game programming on android,开发者_JAVA百科 and all of them provide basically the same solution as to drawing the game, that is having a dedicated thread spinning like this:

public void run() { 
    while(true) { 
        if(!surfaceHolder.getSurface().isValid()) continue; 
        Canvas canvas = surfaceHolder.lockCanvas(); 
        drawGame(canvas); /* do actual drawing here */
        surfaceHolder.unlockCanvasAndPost(canvas); 
    }
} 

now I'm wondering, isn't this wasteful? Suppose I've a game with very simple graphics, so that the actual time in drawGame is little; then I'm going to draw the same things on and on, stealing cpu from the other threads; a possibility could be skipping the drawing and sleeping a bit if the game state hasn't changed, which I could check by having the state update thread mantaining a suitable status flag. But maybe there are other options. For example, couldn'it be possible to synchronize with rendering, so that I don't post updates too often? Or am I missing something and that is precisely what lockCanvas does, that is it blocks and burns no cpu until proper time?

Thanks in advance

L.

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I would say the tutorials you have seen are wrong, you really want to wait in the main loop. 16 milliseconds would be the target frame time in the example below

public void run() { 
    while(true) { 
        long start = System.currentTimeMillis();
        if(!surfaceHolder.getSurface().isValid()) continue; 
        Canvas canvas = surfaceHolder.lockCanvas(); 
        drawGame(canvas); /* do actual drawing here */
        surfaceHolder.unlockCanvasAndPost(canvas); 
        long frameTime =  System.currentTimeMillis() - start;
        try {
            Thread.sleep(Math.max(0, 16 - ( frameTime )));
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
    }
} 

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You don't need to draw canvas from a loop in a thread, you can do this on request, like when moving the finger over the screen.

If the animation is not intensive, one can use just a custom view and then invalidate() the view from some user input event.

It is also possible to stop the thread and then create and start it again, as many time as needed witin the same SurfaceView class.