ios - UIPinchGestureRecognizer仅用于捏出

我正在尝试创建一个UIPinchGestureRecognizer，如果用户捏出手指（将手指分开移动）会失败。我知道有一种非常简单的方法，只需在动作方法中使用识别器的标度即可，如果大于1，则设置一个标志并忽略所有将来的调用。但是，这对我不起作用，我还有其他手势识别器要求该捏捏识别器出现故障，因此当用户向错误的方向捏捏时，我需要使其正确失败。

我试图子类化UIPinchGestureRecognizer：

@implementation BHDetailPinchGestureRecogniser {
    CGFloat initialDistance;
}

#pragma mark - Object Lifecycle Methods

- (id)initWithTarget:(id)target action:(SEL)action {
    self = [super initWithTarget:target action:action];
    if (self) {
        initialDistance = NSNotFound;
    }
    return self;
}

#pragma mark - UIGestureRecogniser Methods

- (BOOL)shouldBeRequiredToFailByGestureRecognizer:(UIGestureRecognizer *)recogniser {
    if ([recogniser isKindOfClass:[UIPinchGestureRecognizer class]]) {
        return [self.delegate gestureRecognizerShouldBegin:self];
    } else return false;
}

- (void)reset {
    [super reset];
    initialDistance = NSNotFound;
}

#pragma mark - Touch Handling Methods

- (void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event {
    if (touches.count >= 2) {
        if (self.state == UIGestureRecognizerStatePossible) {
            // Keep hold of the distance between the touches
            NSArray *bothTouches = [touches allObjects];
            CGPoint location1 = [(UITouch *)bothTouches[0] locationInView:self.view];
            CGPoint location2 = [(UITouch *)bothTouches[1] locationInView:self.view];
            initialDistance = [self distanceBetweenPoint:location1 andPoint:location2];
        }
    } else {
        // Fail if there is only one touch
        self.state = UIGestureRecognizerStateFailed;
    }
}

- (void)touchesMoved:(NSSet *)touches withEvent:(UIEvent *)event {
    NSLog(@"Moved. (tc, %lu) (state, %i) (id, %f)", (unsigned long)touches.count, self.state, initialDistance);
    if (touches.count >= 2) {
        if (self.state == UIGestureRecognizerStatePossible) {
            if (initialDistance != NSNotFound) {
                // Get the new distance and see if is is larger or smaller than the original
                NSArray *bothTouches = [touches allObjects];
                CGPoint location1 = [(UITouch *)bothTouches[0] locationInView:self.view];
                CGPoint location2 = [(UITouch *)bothTouches[1] locationInView:self.view];
                NSLog(@"Checking distance between points.");
                if ([self distanceBetweenPoint:location1 andPoint:location2] < initialDistance - 3.f) {
                    NSLog(@"Began");
                    self.state = UIGestureRecognizerStateBegan;
                } else if ([self distanceBetweenPoint:location1 andPoint:location2] > initialDistance) {
                    NSLog(@"Failed");
                    self.state = UIGestureRecognizerStateFailed;
                }
            }
        } else {
            self.state = UIGestureRecognizerStateChanged;
        }
    }
}

- (void)touchesEnded:(NSSet *)touches withEvent:(UIEvent *)event {
    if (self.state == UIGestureRecognizerStatePossible) self.state = UIGestureRecognizerStateFailed;
    else [super touchesEnded:touches withEvent:event];
}

- (void)touchesCancelled:(NSSet *)touches withEvent:(UIEvent *)event {
    self.state = UIGestureRecognizerStateCancelled;
}

#pragma mark - Helper Methods

- (CGFloat)distanceBetweenPoint:(CGPoint)point1 andPoint:(CGPoint)point2 {
    return sqrtf(powf(point1.x - point2.x, 2) + powf(point1.y - point2.y, 2));
}

@end

我已经意识到，它并不是那么简单，它需要处理多个触摸，有时移动的触摸只有一个触摸，因此需要保持触摸，一个触摸可能结束而另一个开始，而这仍然是捏的一部分。当我想要做的就是如果用户按错误的方向挤压时，使挤压识别器失败，这似乎使我失去了挤压识别器的内置功能。

是否有一种无需完全重写UIPinchGestureRecognizer即可实现此行为的简单方法？可能值得一提的是，我无法控制我想失败的其他识别器（它们位于PSPDFViewController（第三方库）的底下）。

最佳答案

如何使用手势识别器的delegate提供帮助？

使用gestureRecognizerShouldBegin的以下实现设置委托

func gestureRecognizerShouldBegin(gestureRecognizer: UIGestureRecognizer) -> Bool {
    if let pinch = gestureRecognizer as? UIPinchGestureRecognizer {
        return pinch.scale < 1
    }
    return true
}