Android：在画布上的另一个矩形上绘制矩形

Question

I'm trying to draw one rectangle that's light gray over another rectangle that's white on a canvas, but it doesn't seem to do anything. Here's what I've got:

public void onDraw(Canvas c) {
    Paint paint = new Paint();
    paint.setColor(Color.LTGRAY);
    c.drawRect(0, 0, width, height, paint);
    paint.setColor(Color.WHITE);
    c.drawRect(10, 10, width - 10, height - 10, paint); //This is slightly smaller than the gray rectangle, so it looks kinda like a border.
}

To display this, I use setContentView() in the main activity to set the view to a new class extending SurfaceView. When the surface is created in the custom SurfaceView, it starts a thread that executes onDraw() every 100 milliseconds. I got the Canvas by using holder.lockCanvas(), then onDraw()ing and holder.unlockCanvasAndPost(c).

Answer 1

Where are you initializing your width and height ? Are they set to 0? Try calling canvas.getWidth() or canvas.getHeight() .