DrawLine在android2.2中不起作用，为什么？

Question

当以下代码在android 2.3的模拟器上执行时，它有效，但在android 2.2上运行时，没有任何内容出现......为什么？

public class BubbleView extends View {

    Paint paint,paint2;

    int pos, x2,y2;

    public BubbleView(Context context) {
        super(context);
        init();
    }

    private void init(){
        paint = new Paint();
        paint.setAntiAlias(true);
        paint.setStrokeWidth(5);
        paint.setTextSize(25);
        paint.setStyle(Paint.Style.STROKE);
        paint.setColor(Color.GREEN);



        paint2 = new Paint();
        paint2.setAntiAlias(true);
        paint2.setStrokeWidth(5);
        paint2.setTextSize(25);
        paint2.setStyle(Paint.Style.STROKE);
        paint2.setColor(Color.WHITE);
    }

    @Override
    public void onDraw(Canvas canvas){
        int x = getMeasuredWidth()/2;
        int y = getMeasuredHeight()/2;
        float r = Math.max(x, y)*0.6f;
        canvas.drawCircle(x, y, 12 , paint);
        canvas.drawCircle(x, y, r , paint);
        canvas.drawLine(x-r, y, x+r, y, paint);
        canvas.drawLine(x, y-r, x, y+r, paint);

    }

}