如何添加UIGestureRecognizer来绘制弧线，椭圆，线等？

Question

我使用CGContextAddArc创建了“ball”。我的想法是为它添加点击和平移手势。

- (void)drawBallAtPoint:(CGPoint)centerPoint inContext:(CGContextRef)context {
    UIGraphicsPushContext(context);
    CGContextBeginPath(context);

    CGContextMoveToPoint(context, centerPoint.x,centerPoint.y);
    CGContextAddArc(context, centerPoint.x, centerPoint.y, 30, 0.0, 2*M_PI, NO);    CGContextFillPath(context);
    UIGraphicsPopContext();
}

我知道如何判断当前触摸的是“球”，但这只适用于轻拍手势。

- (BOOL)isPointInBall:(CGPoint)point {
    CGRect ballTouchRect = CGRectMake(self.ballCenterPoint.x - kBallRadius, self.ballCenterPoint.y - kBallRadius, kBallRadius*2, kBallRadius*2);
    return CGRectContainsPoint(ballTouchRect, point);
}

在panGesture中它无法正常工作

- (void)panGestureHappened:(UIPanGestureRecognizer *)panGestureRecognizer {
    CGPoint tapLocation = [panGestureRecognizer locationInView:self];
    if ([self isPointInBall:tapLocation]) {
         self.canBETouched = YES;
        NSLog(@"START");
    }
    switch (panGestureRecognizer.state) {
        case UIGestureRecognizerStateBegan:{
            self.touched = YES;
            NSLog(@"BEGAN");

            break;
        }
        case UIGestureRecognizerStateChanged: {

            if (self.canBETouched) {


                CGFloat radius = [self sliderRadius];
                CGPoint sliderCenter = CGPointMake(self.bounds.size.width/2, self.bounds.size.height/2);
                CGPoint sliderStartPoint = CGPointMake(sliderCenter.x, sliderCenter.y - radius);
                CGFloat angle = angleBetweenThreePoints(sliderCenter, sliderStartPoint, tapLocation);

                if (angle < 0) {
                    angle = -angle;
                }
                else {
                    angle = 2*M_PI - angle;
                }

                self.value = translateValueFromSourceIntervalToDestinationInterval(angle, 0, 2*M_PI, self.minimumValue, self.maximumValue);
            }

            break;
        }
        case UIGestureRecognizerStateEnded:{
            self.touched = NO;
            self.canBETouched = NO;

            break;
        }
        default:
            break;
    }
}

它只有作用，如果触摸从“球”开始然后然后它在“球”内滑动。如果触摸开始于“球”，它就不会响应。

那么，我怎样才能在这个球上添加panGesture？