为什么UIAlertView阻止显示我的模式视图控制器? [英] Why UIAlertView prevents my modal view controller from being displayed?

问题描述

比方说，当用户按下按钮时，需要显示一条消息，然后显示一个模态视图控制器. 我会写这样的东西:

Let's say that when the user presses a button a message needs to be shown and then a modal view controller is displayed. I would write something like that :

- (void)pickImageButtonPressed:(id)button {

    UIAlertView *alert = [[UIAlertView alloc] initWithTitle:@"Alert"
                                                    message:@"Some alert"
                                                   delegate:nil
                                          cancelButtonTitle:@"OK"
                                          otherButtonTitles:nil];
    [alert show];
    [alert release];

    UIImagePickerController *picker = [[UIImagePickerController alloc] init];
    picker.delegate = self;
    picker.sourceType = UIImagePickerControllerSourceTypePhotoLibrary;
    [[UIApplication sharedApplication].keyWindow.rootViewController
     presentModalViewController:picker animated:YES];
    [picker release];
}

使用此代码，模态视图控制器根本不会显示！

但是，如果我切换两个代码段(先显示模式，然后显示警报)，则视图控制器将以模态显示，并且警报将完全按照我的意愿显示在其上方.

However, if I switch the two blocks of code (show modal first, then show the alert), the view controller is displayed modally and the alert shows up above it, exactly as I want.

我的问题是:为什么警报阻止显示模式视图控制器?

请注意，我不想在调用 presentModalViewController 之前等待警报消失.

Please note that I do not want to wait for alert to be dismissed before calling presentModalViewController.

更新: 我发现我的生产代码比我最初介绍的要复杂一些.我更新了示例代码，然后终于找到一个简单的示例来重现该问题.

Update : I figured out that my production code was a bit more complicated than what I first put. I updated the example code and then finally found a simple example to reproduce the problem.

请注意，在我的生产代码中，从没有任何对视图控制器的引用的地方显示弹出窗口，这就是为什么我使用 [UIApplication sharedApplication] .keyWindow.rootViewController而不是直接引用的地方到视图控制器

Note that in my production code, the popup is displayed from a place where I don't have any reference to a view controller, that's why I use [UIApplication sharedApplication].keyWindow.rootViewController instead of a direct reference to a view controller

推荐答案

我终于找到了答案.问题确实在这条线上:

I finally found the answer. The issue really was on this line:

[[UIApplication sharedApplication].keyWindow.rootViewController
 presentModalViewController:picker animated:YES];

显示警报时，[UIApplication sharedApplication] .keyWindow.rootViewController 为空！.这就是为什么从不显示选择器的原因.这就是为什么当我切换两个模块时它起作用的原因.

When an alert is displayed, [UIApplication sharedApplication].keyWindow.rootViewController is nil !. That's why the picker was never displayed. And that's why it worked when I switched the two blocks.

现在，我需要找到一种方法，以获取最相关的视图控制器以模态方式呈现选择器...

Now I need to find a way to get the most relevant view controller to present the picker modally...

这篇关于为什么UIAlertView阻止显示我的模式视图控制器?的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！