View画图中的画图方法

@Override
protected void onDraw(Canvas canvas) {
 super.onDraw(canvas);
 //需要截取原始图片的大小
 Rect srcRect = new Rect(0, 0, bitmap.getWidth(),bitmap.getHeight() );
 //需要画图大小
 Rect dstRect = new Rect(0, 0, curLen,barHeight );
 canvas.drawBitmap(bitmap, srcRect, dstRect, null);
}