如何从Appdelegate显示UIAlertController [英] How to show UIAlertController from Appdelegate

问题描述

我在iOS应用上使用PushNotification。我想在应用收到通知时显示UIalertcontroller。

I'm working with PushNotification on iOS app. I would like to show a UIalertcontroller when the app receive a notification.

我在AppDelegate中尝试以下代码：

I try this code below in the AppDelegate:

[self.window.rootViewController presentViewController:alert animated:YES completion:nil];

但UIAlertcontroller显示在根视图（第一个屏幕）中，而对于其他uiviewcontroller，我收到了警告或应用程序崩溃。

But the UIAlertcontroller is showing in the root View (First screen) and for other uiviewcontroller i got warning or the app crashes.

推荐答案

试试这个

目标-C

UIWindow* topWindow = [[UIWindow alloc] initWithFrame:[UIScreen mainScreen].bounds];
topWindow.rootViewController = [UIViewController new];
topWindow.windowLevel = UIWindowLevelAlert + 1;

UIAlertController* alert = [UIAlertController alertControllerWithTitle:@"APNS" message:@"received Notification" preferredStyle:UIAlertControllerStyleAlert];

[alert addAction:[UIAlertAction actionWithTitle:NSLocalizedString(@"OK",@"confirm") style:UIAlertActionStyleCancel handler:^(UIAlertAction * _Nonnull action) {
    // continue your work

    // important to hide the window after work completed.
    // this also keeps a reference to the window until the action is invoked.
    topWindow.hidden = YES; // if you want to hide the topwindow then use this
    topWindow = nil; // if you want to remove the topwindow then use this 
}]];

[topWindow makeKeyAndVisible];
[topWindow.rootViewController presentViewController:alert animated:YES completion:nil];

Swift3

var topWindow: UIWindow? = UIWindow(frame: UIScreen.main.bounds)
topWindow.rootViewController = UIViewController()
topWindow.windowLevel = UIWindowLevelAlert + 1
let alert = UIAlertController(title: "APNS", message: "received Notification", preferredStyle: .alert)
alert.addAction(UIAlertAction(title: NSLocalizedString("OK", comment: "confirm"), style: .cancel, handler: {(_ action: UIAlertAction) -> Void in
    // continue your work

    // important to hide the window after work completed.
    // this also keeps a reference to the window until the action is invoked.
    topWindow.isHidden = true // if you want to hide the topwindow then use this
    topWindow = nil // if you want to hide the topwindow then use this
}))
topWindow.makeKeyAndVisible()
topWindow.rootViewController?.present(alert, animated: true, completion: { _ in })

Swift

var topWindow: UIWindow? = UIWindow(frame: UIScreen.mainScreen().bounds)
topWindow.rootViewController = UIViewController()
topWindow.windowLevel = UIWindowLevelAlert + 1
var alert: UIAlertController =  UIAlertController.alertControllerWithTitle("APNS", message: "received Notification", preferredStyle: .Alert)
alert.addAction(UIAlertAction.actionWithTitle(NSLocalizedString("OK", "confirm"), style: .Cancel, handler: {(action: UIAlertAction) -> Void in
    // continue your work

    // important to hide the window after work completed.
    // this also keeps a reference to the window until the action is invoked.
    topWindow.hidden = true // if you want to hide the topwindow then use this
    topWindow = nil // if you want to remove the topwindow then use this 
}))
topWindow.makeKeyAndVisible()
topWindow.rootViewController.presentViewController(alert, animated: true, completion: { _ in })

详细说明： http://www.thecave.com/2015/09/28/how-to-present-an-alert-view-using-uialertcontroller-when-you-dont-have-a-view- controller /

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