场景:用户点击视图控制器上的按钮。视图控制器是导航堆栈中最顶层的(很明显)。tap调用在另一个类上调用的实用程序类方法。这里发生了不好的事情我想在控件返回到视图控制器之前在那里显示一个警告。

+ (void)myUtilityMethod {
    // do stuff
    // something bad happened, display an alert.
}

这是可能的UIAlertView(但可能不太合适)。

在这种情况下,你如何在myUtilityMethod中呈现UIAlertController ?


当前回答

以下是mythicalcoder的答案,作为一个扩展,在Swift 4中测试和工作:

extension UIAlertController {

    func presentInOwnWindow(animated: Bool, completion: (() -> Void)?) {
        let alertWindow = UIWindow(frame: UIScreen.main.bounds)
        alertWindow.rootViewController = UIViewController()
        alertWindow.windowLevel = UIWindowLevelAlert + 1
        alertWindow.makeKeyAndVisible()
        alertWindow.rootViewController?.present(self, animated: animated, completion: completion)
    }

}

使用示例:

let alertController = UIAlertController(title: "<Alert Title>", message: "<Alert Message>", preferredStyle: .alert)
alertController.addAction(UIAlertAction(title: "Close", style: .cancel, handler: nil))
alertController.presentInOwnWindow(animated: true, completion: {
    print("completed")
})

其他回答

另一个选择:

    var topController:UIViewController = UIApplication.shared.keyWindow!.rootViewController!
    while ((topController.presentedViewController) != nil) {
        topController = topController.presentedViewController!
    }
    topController.present(alert, animated:true, completion:nil)

创建扩展像在Aviel Gross回答。这里有Objective-C扩展。

这里有头文件*.h

//  UIAlertController+Showable.h

#import <UIKit/UIKit.h>

@interface UIAlertController (Showable)

- (void)show;

- (void)presentAnimated:(BOOL)animated
             completion:(void (^)(void))completion;

- (void)presentFromController:(UIViewController *)viewController
                     animated:(BOOL)animated
                   completion:(void (^)(void))completion;

@end

和实现:*.m

//  UIAlertController+Showable.m

#import "UIAlertController+Showable.h"

@implementation UIAlertController (Showable)

- (void)show
{
    [self presentAnimated:YES completion:nil];
}

- (void)presentAnimated:(BOOL)animated
             completion:(void (^)(void))completion
{
    UIViewController *rootVC = [UIApplication sharedApplication].keyWindow.rootViewController;
    if (rootVC != nil) {
        [self presentFromController:rootVC animated:animated completion:completion];
    }
}

- (void)presentFromController:(UIViewController *)viewController
                     animated:(BOOL)animated
                   completion:(void (^)(void))completion
{

    if ([viewController isKindOfClass:[UINavigationController class]]) {
        UIViewController *visibleVC = ((UINavigationController *)viewController).visibleViewController;
        [self presentFromController:visibleVC animated:animated completion:completion];
    } else if ([viewController isKindOfClass:[UITabBarController class]]) {
        UIViewController *selectedVC = ((UITabBarController *)viewController).selectedViewController;
        [self presentFromController:selectedVC animated:animated completion:completion];
    } else {
        [viewController presentViewController:self animated:animated completion:completion];
    }
}

@end

你在你的实现文件中使用这个扩展,就像这样:

#import "UIAlertController+Showable.h"

UIAlertController* alert = [UIAlertController
    alertControllerWithTitle:@"Title here"
                     message:@"Detail message here"
              preferredStyle:UIAlertControllerStyleAlert];

UIAlertAction* defaultAction = [UIAlertAction
    actionWithTitle:@"OK"
              style:UIAlertActionStyleDefault
            handler:^(UIAlertAction * action) {}];
[alert addAction:defaultAction];

// Add more actions if needed

[alert show];

交叉张贴我的答案,因为这两个线程没有被标记为欺骗…

现在UIViewController是responder chain的一部分,你可以这样做:

if let vc = self.nextResponder()?.targetForAction(#selector(UIViewController.presentViewController(_:animated:completion:)), withSender: self) as? UIViewController {

    let alert = UIAlertController(title: "A snappy title", message: "Something bad happened", preferredStyle: .Alert)
    alert.addAction(UIAlertAction(title: "OK", style: .Default, handler: nil))

    vc.presentViewController(alert, animated: true, completion: nil)
}

@agilityvision的答案翻译为Swift4/iOS11。我没有使用本地化字符串,但你可以很容易地改变:

import UIKit

/** An alert controller that can be called without a view controller.
 Creates a blank view controller and presents itself over that
 **/
class AlertPlusViewController: UIAlertController {

    private var alertWindow: UIWindow?

    override func viewDidLoad() {
        super.viewDidLoad()
    }

    override func viewDidDisappear(_ animated: Bool) {
        super.viewDidDisappear(animated)
        self.alertWindow?.isHidden = true
        alertWindow = nil
    }

    func show() {
        self.showAnimated(animated: true)
    }

    func showAnimated(animated _: Bool) {

        let blankViewController = UIViewController()
        blankViewController.view.backgroundColor = UIColor.clear

        let window = UIWindow(frame: UIScreen.main.bounds)
        window.rootViewController = blankViewController
        window.backgroundColor = UIColor.clear
        window.windowLevel = UIWindowLevelAlert + 1
        window.makeKeyAndVisible()
        self.alertWindow = window

        blankViewController.present(self, animated: true, completion: nil)
    }

    func presentOkayAlertWithTitle(title: String?, message: String?) {

        let alertController = AlertPlusViewController(title: title, message: message, preferredStyle: .alert)
        let okayAction = UIAlertAction(title: "Ok", style: .default, handler: nil)
        alertController.addAction(okayAction)
        alertController.show()
    }

    func presentOkayAlertWithError(error: NSError?) {
        let title = "Error"
        let message = error?.localizedDescription
        presentOkayAlertWithTitle(title: title, message: message)
    }
}

在调用类方法之前注册通知。

斯威夫特代码:

NSNotificationCenter.defaultCenter().addObserver(self, selector: "displayAlert", name: "ErrorOccured", object: nil)

在displayAlert实例方法中,您可以显示警报。