自己定义的Layout，onDraw（）方法未调用

我定义了一个这样的类：

public class TestMyFrameLayout extends FrameLayout{

    Paint mPaint;
    public TestMyFrameLayout(Context context, AttributeSet attrs) {
        super(context, attrs);
    }

    public TestMyFrameLayout(Context context) {
        super(context);
        mPaint = new Paint();
        mPaint.setColor(Color.GREEN);
    }

    protected void onDraw(Canvas canvas) {
        super.onDraw(canvas);
        canvas.drawCircle(50f, 50f, 30, mPaint);
    }   
}

并这样称呼它：

TestMyFrameLayout myFrameLayout = new TestMyFrameLayout(this);
LayoutParams myFrameLayoutParams = new LayoutParams(300,300);
myFrameLayout.setLayoutParams(myFrameLayoutParams);
setContentView(myFrameLayout);

但是实际上TestMyFrameLayout.onDraw（Canvas canvas）函数没有被调用，为什么？

解决了。添加 this.setWillNotDraw(false); 构造函数