java – Android自定义视图只能调用onDraw一次

然后在xml中添加视图并设置android：background.

视图正确呈现但不更新.一些调试显示onDraw只被调用一次.缺什么？

我的自定义视图的代码：

public class Gmeter extends ImageView {
    private Bitmap dot;
    private float dotHeight,dotWidth;

    public Gmeter(Context context,AttributeSet attrs) {
        super(context,attrs);

        dot = BitmapFactory.decodeResource(getContext().getResources(),R.drawable.g_dot);
        dotWidth = dot.getWidth();
        dotHeight = dot.getHeight();
    }

    @Override
    protected void onDraw(Canvas canvas){
        super.onDraw(canvas);

        float dataX =(float) Data.getX();

        float x = (getWidth()-dotWidth)/2f;
        float y = (getHeight()-dotHeight)/2f;

        x+= dataX * getWidth() /2f;

        canvas.drawBitmap(dot,x,y,null);
    }

}