如果已显示警报，则显示UIAlertController

问题描述

遗留的 UIAlertView 与新的 UIAlertController 之间的区别在于后者需要呈现在特定的viewcontroller上使用 presentViewController：animated：completion：。这给我的用例带来了一个尴尬的问题：当第二个视图控制器出现时，如果已经有 UIAlertController 显示（例如评级对话框）（例如，由于网络连接失败）。我经历过，在这种情况下，第二个 UIAlertController 只是没有显示。

Difference between the legacy UIAlertView and the new UIAlertController is that the latter needs to be presented onto a specific viewcontroller with presentViewController:animated:completion:. This poses an awkward problem for my use case: what if there is already an UIAlertController showing (e.g. a rating dialog) when a second viewcontroller gets presented (e.g. an error dialog due to failed network connection). I have experienced that in this case the second UIAlertController just does not show.

编辑：目前我尝试为了显示警报，我不知道目前是否有任何呈现。

At the moment I try to show an alert, I do not know if there currently is anything presenting.

你如何应对这种情况？

推荐答案

我找到了一个解决方法，找出我可以提出警报的视图控制器。我还发布了的答案：

I found a workaround to find out which viewcontroller I can present the alert upon. I also posted the answer here:

@implementation UIViewController (visibleViewController)

- (UIViewController *)my_visibleViewController {

    if ([self isKindOfClass:[UINavigationController class]]) {
        // do not use method visibleViewController as the presentedViewController could beingDismissed
        return [[(UINavigationController *)self topViewController] my_visibleViewController];
    }

    if ([self isKindOfClass:[UITabBarController class]]) {
        return [[(UITabBarController *)self selectedViewController] my_visibleViewController];
    }

    if (self.presentedViewController == nil || self.presentedViewController.isBeingDismissed) {
        return self;
    }

    return [self.presentedViewController my_visibleViewController];
}

@end

// To show a UIAlertController, present on the following viewcontroller:
UIViewController *visibleViewController = [[UIApplication sharedApplication].delegate.window.rootViewController my_visibleViewController];

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