UILongPressGestureRecognizer长按事件

最近发现项目中有多处列表页都不能侧滑返回，公司没有产品经理，这样对于8P这样的屏幕体验非常的差， 我就添加统一的侧滑返回，期间遇到遇见一个有关长按手势不执行的问题。

问题描述:

给UITableView的cell添加了长按手势，当长按cell时UILongPressGestureRecognizer事件不响应，只有手指移动和手指松开时长按事件才会被执行

问题排查

初步判断多个手势冲突， 问题应该由添加侧滑返回的代码出现了问题，侧滑返回我使用了UINavigationController+TZPopGesture分类，通过一个方法即可实现。
查看其实现，发现它是给scrollView添加一个UIPanGestureRecognizer拖动手势，当这个拖动手势响应时，执行navigationController的侧滑返回手势，触发侧滑返回，
另外还在UINavigationController中 实现了self.interactivePopGestureRecognizer.delegate；
我发现问题应该出在这块，便注释了部分手势的代理方法，发现tableViewCell的长按手势可正常响应了；
最终确定问题发生在- (BOOL)gestureRecognizer:(UIGestureRecognizer *)gestureRecognizer shouldBeRequiredToFailByGestureRecognizer:(UIGestureRecognizer *)otherGestureRecognizer方法内， 最初的时候为了解决只有在系统侧滑手势失败时，才去触发ScrollView的滑动，此方法return YES；

此方法有两个参数为两个手势，意思为只有当gestureRecognizer被判断侦测失败了，才可以侦测otherGestureRecognizer,
当我长按cell时，长按手势为otherGestureRecognizer，而此时gestureRecognizer为我们为scrollView添加的拖动手势，那此时拖动手势并没有失败，所以长按手势不会被执行到，但当手指移动或松开时gestureRecognizer被侦测失败，此时otherGestureRecognizer长按手势才会被侦测到；

解决方法

处理添加的侧滑返回手势和长按手势冲突，当当前手势gestureRecognizer是侧滑返回手势时，同时处理otherGestureRecognizer

- (BOOL)gestureRecognizer:(UIGestureRecognizer *)gestureRecognizer shouldBeRequiredToFailByGestureRecognizer:(UIGestureRecognizer *)otherGestureRecognizer {
    // 此处导致使用此分类的界面长按时不能及时响应，只有手指移动、松开手指时才会响应长按手势
    UIViewController *vc = self.topViewController;
    if ([gestureRecognizer isEqual:vc.tz_popGestureRecognizer]) {
        return NO;
    }
    return YES;
}

总结

• 通过Xcode文档发现，这两个api是在iOS7时添加的

// called once per attempt to recognize, so failure requirements can be determined lazily and may be set up between recognizers across view hierarchies
// return YES to set up a dynamic failure requirement between gestureRecognizer and otherGestureRecognizer
//
// note: returning YES is guaranteed to set up the failure requirement. returning NO does not guarantee that there will not be a failure requirement as the other gesture's counterpart delegate or subclass methods may return YES
- (BOOL)gestureRecognizer:(UIGestureRecognizer *)gestureRecognizer shouldRequireFailureOfGestureRecognizer:(UIGestureRecognizer *)otherGestureRecognizer NS_AVAILABLE_IOS(7_0);
- (BOOL)gestureRecognizer:(UIGestureRecognizer *)gestureRecognizer shouldBeRequiredToFailByGestureRecognizer:(UIGestureRecognizer *)otherGestureRecognizer NS_AVAILABLE_IOS(7_0);

• 说明

- (BOOL)gestureRecognizer:(UIGestureRecognizer *)gestureRecognizer shouldRequireFailureOfGestureRecognizer:(UIGestureRecognizer *)otherGestureRecognizer NS_AVAILABLE_IOS(7_0);

此方法指定只有gestureRecognizer被系统判定失败时，才会执行otherGestureRecognizer

- (BOOL)gestureRecognizer:(UIGestureRecognizer *)gestureRecognizer shouldBeRequiredToFailByGestureRecognizer:(UIGestureRecognizer *)otherGestureRecognizer NS_AVAILABLE_IOS(7_0);

此方法指定只有otherGestureRecognizer被系统判定失败时，才会执行gestureRecognizer

由于这两个方法比较相似，所以用的时候还是要注意使用场景，不要弄混了。