UIAlertView show() behavior for UIAlertController

问题:

In previous versions of iOS I was able to call show on a UIAlertView in the App Delegate. More specifically, show was called in:

func applicationDidBecomeActive(application: UIApplication)

Since UIAlertViews disregarded the view hierarchy in most cases, this solution worked no matter where the user was in the app.

With the introduction of UIAlertController this problem becomes a little trickier. UIAlertController is now a subclass of UIViewController and needs to be presented just like any other UIViewController. While presenting the UIAlertController from the keyWindow's rootViewController works, it's not the ideal solution.

Does anyone have any ideas on replicating [UIAlertView show] functionality for a UIAlertController? Any way to show the UIAlertController on app active without traversing the view hierarchy?

回答1:

I figured out a solution that I believe to be more elegant than the answer I posted previously. I'll copy and paste the answer I posted to a similar question. Follow the link at the bottom of my post if you just want to see the code.

The solution is to use an additional UIWindow.

When you want to display your UIAlertController:

1. Make your window the key and visible window (window.makeKeyAndVisible())
2. Just use a plain UIViewController instance as the rootViewController of the new window. (window.rootViewController = UIViewController())
3. Present your UIAlertController on your window's rootViewController

A couple things to note:

• Your UIWindow must be strongly referenced. If it's not strongly referenced it will never appear (because it is released). I recommend using a property, but I've also had success with an associated object.
• To ensure that the window appears above everything else (including system UIAlertControllers), I set the windowLevel. (window.windowLevel = UIWindowLevelAlert + 1)

Lastly, I have a completed implementation if you just want to look at that.

https://github.com/dbettermann/DBAlertController

回答2:

Here's what I ended up with:

public class func visibleViewController() -> UIViewController? {
    return self.visibleViewController(UIApplication.sharedApplication().keyWindow?.rootViewController?)
}

private class func visibleViewController(viewController: UIViewController?) -> UIViewController? {
    if viewController?.presentedViewController == nil {
        println("Visible view controller: \(viewController)")
        return viewController
    } else if let navigationController = viewController as? UINavigationController {
        return self.visibleViewController(navigationController.topViewController)
    } else if let tabBarController = viewController as? UITabBarController {
        return self.visibleViewController(tabBarController.selectedViewController)
    } else {
        return self.visibleViewController(viewController?.presentedViewController)
    }
}

回答3:

Try This

    UIAlertController * alert=   [UIAlertController
                                  alertControllerWithTitle:@"title"
                                  message:@" Your message hear"
                                  preferredStyle:UIAlertControllerStyleAlert];

    UIAlertAction *okBtnAction = [UIAlertAction actionWithTitle:@"Ok" style:UIAlertActionStyleDefault handler:^(UIAlertAction *action){
        //Do what action u want.
        [alert dismissViewControllerAnimated:YES completion:nil];
    }];
    [alert addAction:okAction];

     UIAlertAction *cancelAction = [UIAlertAction actionWithTitle:@"cancel" style:UIAlertActionStyleDefault handler:^(UIAlertAction *action){
            [alert dismissViewControllerAnimated:YES completion:nil];
            //do something when click button
        }];
        [alert addAction:Action];

    UIViewController *vc = [[[[UIApplication sharedApplication] delegate] window] rootViewController];
    [vc presentViewController:alert animated:YES completion:nil];

回答4:

Try using JSAlertView which handles both UIAlertView and UIAlertController APIs. It provides short and easy methods for displaying alerts and handles multiple alerts fired at same time, very well.