如何更新SurfaceView？

我扩展了SurfaceView并设法在Activity中绘制它.Activity应该能够在我的SurfaceView上调用一个方法来改变一些参数并重绘它.如何实现更新功能？

这是我的班级:

public class MySurfaceView extends SurfaceView
                                    implements SurfaceHolder.Callback {

    private int circleRadius = 50;
    private SurfaceHolder sh;
    private final Paint paint = new Paint(Paint.ANTI_ALIAS_FLAG);

    public MySurfaceView(Context context, AttributeSet as) {
        super(context,as);
        sh = getHolder();
        sh.addCallback(this);
        paint.setColor(Color.BLUE);
        paint.setStyle(Style.FILL);
    }
    public void surfaceCreated(SurfaceHolder holder) {
        Canvas canvas = sh.lockCanvas();
        canvas.drawColor(Color.BLACK);
        canvas.drawCircle(100, 200, circleRadius, paint);
        sh.unlockCanvasAndPost(canvas);
    }
    public void update( newRadius ) {
        circleRadius = newRadius;
        // What more?
    }
}

update重绘一切应包含哪些内容？这与此有关surfaceChanged吗？

该update函数应调用invalidate()或postInvalidate()按顺序重绘View.

此外,SurfaceViews默认禁用重绘.通过调用setWillNotDraw(false)例如启用它surfaceCreated.