Android:lockCanvas() 和 lockCanvas(null) 有什么区别？

Question

标题说的很清楚，不过我会给出一个代码示例以防万一。这是来自 Android SDK 中的 LunarLander 示例:

    @Override
    public void run() {
        while (mRun) {
            Canvas c = null;
            try {
                c = mSurfaceHolder.lockCanvas(null);
                synchronized (mSurfaceHolder) {
                    if (mMode == STATE_RUNNING) updatePhysics();
                    doDraw(c);
                }
            } finally {
                // do this in a finally so that if an exception is thrown
                // during the above, we don't leave the Surface in an
                // inconsistent state
                if (c != null) {
                    mSurfaceHolder.unlockCanvasAndPost(c);
                }
            }
        }
    }

lockCanvas() 的文档说所有像素都必须重新绘制，而 lockCanvas(Rect dirty) 说你只需要重新绘制像素脏。我看到将 null 传递给此函数的两种可能的解释:它不需要重新绘制任何像素，或者以与 lockCanvas() 相同的方式运行。

Answer 1

它是开源的

public Canvas lockCanvas() {
  return internalLockCanvas(null);
}
public Canvas lockCanvas(Rect dirty) {
  return internalLockCanvas(dirty);
}