自定义view画圆跟着鼠标移动

public class BallView extends View{

private Paint paint;
private int cx=100;
private int cy=100;

public BallView(Context context) {
super(context);
}

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

}

@Override
public boolean onTouchEvent(MotionEvent event) {

switch (event.getAction()){
case MotionEvent.ACTION_DOWN:

break;
case MotionEvent.ACTION_MOVE:
cx = (int) event.getX();
cy = (int) event.getY();

invalidate();
break;
case MotionEvent.ACTION_UP:

break;
}
return true;
}

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

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

//创建一个画笔
paint = new Paint();
// 抗锯齿
paint.setAntiAlias(true);
//设置画笔的颜色
paint.setColor(Color.RED);
//设置画笔 填充是空心的
paint.setStyle(Paint.Style.FILL);

canvas.drawCircle(cx, cy, 100, paint);

}
}