Question

I was trying to make moving bitmap with accelerometer smoother and accidentally noticed that when I call invalidate(); at the end of onDraw() method instead of calling it at the end of onSensorChanged() I get much smoother movement, even if I don’t have any kind of low-pass filters. Then I tried to do the same with my LiveWallpaper, but as you know there is no onDraw() method in Engine of WallpaperService, but you have to create one yourself and call it for example with Handler. But doing it that way doesn’t give any smoother result even if the rest of the code is same as in other programs.

This is the code that I use in my non-Wallpaper programs and it works fine:

public void onDraw(Canvas c) {

xPosition += xAcceleration;
yPosition += yAcceleration;

drawable = BitmapFactory.decodeResource(getResources(),R.drawable.ball);
c.drawBitmap(drawable, xPosition,yPosition, paint);

invalidate();

}

So I went and tried to create my own invalidate-like solution for WallpaperService and came up with this:

void drawFrame() {
final SurfaceHolder holder = getSurfaceHolder();

Canvas c = null;
try {
c = holder.lockCanvas();
if (c != null) {
xPosition += xAcceleration;
yPosition += yAcceleration;

background = BitmapFactory.decodeResource(getResources(),R.drawable.bg);
drawable = BitmapFactory.decodeResource(getResources(),R.drawable.ball);

c.drawBitmap(background, 0,0, null);
c.drawBitmap(drawable, xPosition,yPosition, null);
}
} catch (Exception ex){
}
holder.unlockCanvasAndPost(c);
drawFrame();
}

So what I am doing is:

1. Get Canvas.
2. Draw on Canvas.
3. Unlock Canvas and start over.

As I have understood this should give me invalidate();-like behaviour, but instead it tries to show wallpaper and after while it gives me StackOverflowError.

Answer 1

Ok I got this solved already. All I had to to was move bitmap initializations into onCreate() method.