Android自定义View之--理解视图层

public class MyButton extends Button {

public MyButton(Context context, AttributeSet attrs, int defStyle) {
super(context, attrs, defStyle);
}

public MyButton(Context context, AttributeSet attrs) {
super(context, attrs);
}

public MyButton(Context context) {
super(context);
}
@Override
protected void onDraw(Canvas canvas) {
//文本之下
Paint paint = new Paint();
paint.setTextSize(55);
paint.setColor(Color.BLUE);
canvas.drawText("下面", canvas.getWidth()/2, canvas.getHeight()/2, paint);
super.onDraw(canvas);
//文本之上
paint.setColor(Color.RED);
canvas.drawText("上面", canvas.getWidth()/2-100, canvas.getHeight()/2, paint);
}

}