How do i display UIAlertController from any NSObject subclass?

问题

I have a legacy codebase I am managing, which needs to display alert messages from all over the place. This is terrible practice and is in need of a refactor, but that isn't going to happen any time soon. With iOS 9 I need the ability to fire & forget an alert view, and have the view display and queuing managed for me.

回答1:

To show, UIAlertController, we need object of UIViewController So you can use below way to do that.

 UIWindow *keyWindow = [[UIApplication sharedApplication]keyWindow];
 UIViewController *mainController = [keyWindow rootViewController];
 [mainController presentViewController:alert animated:YES completion:nil];

Thanks

回答2:

As other people have suggested, this is generally bad practice and breaks the MVC principles. However, if you're managing a legacy codebase and refactoring everything simply isn't an option, i made this class which lets you treat UIAlertController like the old UIAlertView, it manages displaying the alert from any class, and also queue's alerts for you...

https://github.com/sammio2/SMHAlertController

回答3:

For Display UIAlertController in NSObject class use below code.

        UIAlertController * popup =   [UIAlertController
                                  alertControllerWithTitle:nil
                                  message:nil
                                  preferredStyle:UIAlertControllerStyleActionSheet];

        UIAlertAction* cancel = [UIAlertAction
                                 actionWithTitle:@"Cancel"
                                 style:UIAlertActionStyleCancel
                                 handler:^(UIAlertAction * action) {
                                     [popup dismissViewControllerAnimated:YES completion:nil];
                                 }];
        [popup addAction:cancel];

        UIViewController *rootViewController = [[Helper shareInstance] topViewController];
        [rootViewController presentViewController:popup animated:YES completion:nil];

// Put Below Method in Your Global Helper Class.

    - (UIViewController *)topViewController {
      return [self topViewController:[UIApplication sharedApplication].keyWindow.rootViewController];
    }

    - (UIViewController *)topViewController:(UIViewController *)rootViewController {
        if (rootViewController.presentedViewController == nil) {
            return rootViewController;
        }

        if ([rootViewController.presentedViewController isMemberOfClass:[UINavigationController class]]) {
            UINavigationController *navigationController = (UINavigationController *)rootViewController.presentedViewController;
            UIViewController *lastViewController = [[navigationController viewControllers] lastObject];
            return [self topViewController:lastViewController];
        }

        UIViewController *presentedViewController = (UIViewController *)rootViewController.presentedViewController;
        return [self topViewController:presentedViewController];
    }

来源：https://stackoverflow.com/questions/31472321/how-do-i-display-uialertcontroller-from-any-nsobject-subclass