双击 UICollectionView；需要单击才能失败

Question

遇到与this question 类似的问题，我正在尝试将双击手势识别器添加到我的UICollectionView 实例中。

我需要防止默认单击调用UICollectionViewDelegate方法collectionView:didSelectItemAtIndexPath:。

为了实现这一点，我实现了代码straight from Apple's Collection View Programming Guide (Listing 4-2)：

UITapGestureRecognizer* tapGesture = [[UITapGestureRecognizer alloc] initWithTarget:self action:@selector(handleTapGesture:)];
NSArray* recognizers = [self.collectionView gestureRecognizers];

// Make the default gesture recognizer wait until the custom one fails.
for (UIGestureRecognizer* aRecognizer in recognizers) {
   if ([aRecognizer isKindOfClass:[UITapGestureRecognizer class]])
      [aRecognizer requireGestureRecognizerToFail:tapGesture];
}

// Now add the gesture recognizer to the collection view.
tapGesture.numberOfTapsRequired = 2;
[self.collectionView addGestureRecognizer:tapGesture];

此代码未按预期工作：tapGesture 在双击时触发，但未阻止默认单击，并且仍调用委托的 didSelect... 方法。

在调试器中单步执行会发现 if 条件 [aRecognizer isKindOfClass:[UITapGestureRecognizer class]] 永远不会评估为真，因此新的 tapGesture 上的故障要求未建立。

每次通过for循环运行这个调试器命令：

po (void)NSLog(@"%@",(NSString *)NSStringFromClass([aRecognizer class]))

显示默认手势识别器（确实）不是UITapGestureRecognizer 实例。

相反，它们是私有类 UIScrollViewDelayedTouchesBeganGestureRecognizer 和 UIScrollViewPanGestureRecognizer。

首先，我不能在不违反私有 API 规则的情况下明确使用这些。其次，通过requireGestureRecognizerToFail: 附加到UIScrollViewDelayedTouchesBeganGestureRecognizer 似乎无论如何都不能提供所需的行为——即仍然调用代理的didSelect...。

如何使用UICollectionView 的默认手势识别器向集合视图添加双击并防止默认单击也触发委托的collectionView:didSelectItemAtIndexPath: 方法？

提前致谢！

Answer 1

我的解决方案是不实现 collectionView:didSelectItemAtIndexPath 而是实现两个手势识别器。

    self.doubleTapGesture = [[UITapGestureRecognizer alloc] initWithTarget:self action:@selector(processDoubleTap:)];
    [_doubleTapGesture setNumberOfTapsRequired:2];
    [_doubleTapGesture setNumberOfTouchesRequired:1];   

    [self.view addGestureRecognizer:_doubleTapGesture];

    self.singleTapGesture = [[UITapGestureRecognizer alloc] initWithTarget:self action:@selector(processSingleTap:)];
    [_singleTapGesture setNumberOfTapsRequired:1];
    [_singleTapGesture setNumberOfTouchesRequired:1];
    [_singleTapGesture requireGestureRecognizerToFail:_doubleTapGesture];

    [self.view addGestureRecognizer:_singleTapGesture];

这样我可以处理单击和双击。我能看到的唯一问题是在 doubleTaps 上选择了单元格，但如果这让您感到困扰，您可以在两个选择器中处理它。

Answer 2

我使用以下方法注册一个 UITapGestureRecognizer：

UITapGestureRecognizer* singleTapGesture = [[UITapGestureRecognizer alloc] initWithTarget:self action:@selector(handleSingleTapGesture:)];
singleTapGesture.delaysTouchesBegan = YES;
singleTapGesture.numberOfTapsRequired = 1; // number of taps required
singleTapGesture.numberOfTouchesRequired = 1; // number of finger touches required
[self.collectionView addGestureRecognizer:singleTapGesture];

通过将delaysTouchesBegan 设置为YES，自定义手势识别器通过延迟注册其他触摸事件来获得高于默认集合视图点击侦听器的优先级。或者，您可以通过将cancelsTouchesInView 设置为YES 来完全取消触摸识别。

手势由以下函数处理：

- (void)handleSingleTapGesture:(UITapGestureRecognizer *)sender {

    if (sender.state == UIGestureRecognizerStateEnded) {
        CGPoint location = [sender locationInView:self.collectionsView];
        NSIndexPath *indexPath = [self.collectionsView indexPathForItemAtPoint:location];

        if (indexPath) {
            NSLog(@"Cell view was tapped.");
            UICollectionViewCell *cell = [self.collectionsView cellForItemAtIndexPath:indexPath];
            // Do something.                
        }
    }
    else{
        // Handle other UIGestureRecognizerState's
    }
}