初學自定義view(可拖動圓)

public class SuView extends View {
    private float x = 100;
    private float y = 100;
    public SuView(Context context) {
        super(context);
    }

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

    public SuView(Context context, AttributeSet attrs, int defStyleAttr) {
        super(context, attrs, defStyleAttr);
    }

    @Override
    protected void onDraw(Canvas canvas) {
        super.onDraw(canvas);
        canvas.drawColor(Color.WHITE);//設置畫布顏色
        Paint paint = new Paint();//畫筆
        paint.setColor(Color.RED);//設置畫筆顏色
        paint.setStrokeWidth(10);
        paint.setStyle(Paint.Style.STROKE);
        paint.setAntiAlias(true);//抗鋸齒
        canvas.drawCircle(x,y,100,paint);//畫圓
    }

    @Override
    public boolean onTouchEvent(MotionEvent event) {
        x = event.getX();
        y = event.getY();
        postInvalidate();
        return true;
    }
}