使用dispatchDraw（Canvas）获取视频预览的子部分

Question

以下是SurfaceView子类中的重写dispatchDraw。我正在尝试更改Surface的参数（仅获取视频预览的子部分。

@Override

       public void dispatchDraw (Canvas canvas) {
        Log.d(TAG,"**************inside dispatchDraw************");

        int VIEW_WIDTH = canvas.getWidth(); 
        int VIEW_HEIGHT = canvas.getHeight();
        Log.d(TAG,"**************inside dispatchDraw************" + Integer.toString(VIEW_WIDTH) + " ," + Integer.toString(VIEW_HEIGHT));

        int newWidth = 400;  

        int newHeight = 240; 
        float scaleWidth = ((float) newWidth) / VIEW_WIDTH;  

        float scaleHeight = ((float) newHeight) / VIEW_HEIGHT;  


        Matrix matrix = new Matrix();  

        matrix.postScale(scaleWidth, scaleHeight);  

        canvas.setMatrix(matrix);
        super.dispatchDraw(canvas);
        Log.d(TAG,"**************inside dispatchDraw-after super************");

    }

为什么上面的代码根本不会改变SurfaceView的尺寸？

Answer 1

因为SurfaceView不使用视图层次结构的Canvas来绘制。