延迟呈现模态视图控制器 [英] Delay in presenting a modal view controller

问题描述

我有一个基于标签栏的应用。所有5个选项卡中都有导航控制器，自定义视图控制器实例正确设置为根视图控制器。加载就好了。其中一些视图控制器包含表视图。我想在用户在表视图中选择一行时向用户显示模态视图控制器。 didSelectRowAtIndexPath委托方法的（相关部分）如下所示：

I have a tab bar based app. There are navigation controllers in all 5 tabs with instances of custom view controller setup properly as root view controllers. This loads just fine. A couple of these view controllers contain table views. I want to show a modal view controller to the user when they select a row in the table view. The (relevant part of) didSelectRowAtIndexPath delegate method looks as follows:

SampleSelectorViewController *sampleVC = [[SampleSelectorViewController alloc] init];
[self presentViewController:sampleVC animated:YES completion:NULL];

模态视图控制器出现但是在非常明显的延迟后出现。有时它甚至要求用户第二次点击该行。我已经验证过的一些事情是：

The modal view controller appears BUT it appears after a very noticeable delay. At times it even requires the user to tap the row a second time. A few things that I have already verified are:

• 当用户点击行时，会调用表视图的didSelectRowAtIndexPath方法


• didSelectRowAtIndexPath方法不包含任何阻塞调用。没有执行网络操作，模态视图控制器的设置不涉及任何处理密集型任务。它显示的数据是静态的。


• 如果我将新的视图控制器推到导航堆栈上（其他一切保持完全相同），它的行为完全没有任何延迟。只有在遇到模式时才会遇到延迟。

任何想法/建议？

推荐答案

似乎从 tableView中调用 presentViewController：animated：completion ：didSelectRowAtIndexPath：是有问题的。在仪器中使用Time Profiler时，很难找到任何突出的东西。有时我的模态视图在不到一秒的时间内出现，有时需要4s甚至9s。

It seems calling presentViewController:animated:completion from within tableView:didSelectRowAtIndexPath: is problematic. It's difficult to find anything that stands out when using the Time Profiler in Instruments, also. Sometimes my modal view comes up in less than a second and other times it takes 4s or even 9s.

我认为它与底层的 UIPresentationController有关和布局，这是我在点击一行和在Time Profiler中查看模态演示文稿时选择时间区域时看到的少数几件事之一。

I think it's related to the underlying UIPresentationController and layout, which is one of the few things I see when selecting the region of time between tapping on a row and seeing the modal presentation in the Time Profiler.

雷达存在描述此问题： http://openradar.appspot.com/19563577

A Radar exists describing this issue: http://openradar.appspot.com/19563577

解决方法很简单但不满意：稍微延迟演示文稿以避免引起减速的任何引起争议的行为。

The workaround is simple but unsatisfying: delay the presentation slightly to avoid whatever contentious behavior is causing the slowdown.

dispatch_async(dispatch_get_main_queue(), ^{
   [self presentViewController:nav animated:YES completion:nil];
});

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