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

创建helper类AlertWindow并使用as

let alertWindow = AlertWindow();
let alert = UIAlertController(title: "Hello", message: "message", preferredStyle: .alert);
let cancel = UIAlertAction(title: "Ok", style: .cancel){(action) in

    //....  action code here

    // reference to alertWindow retain it. Every action must have this at end

    alertWindow.isHidden = true;

   //  here AlertWindow.deinit{  }

}
alert.addAction(cancel);
alertWindow.present(alert, animated: true, completion: nil)


class AlertWindow:UIWindow{

    convenience init(){
        self.init(frame:UIScreen.main.bounds);
    }

    override init(frame: CGRect) {
        super.init(frame: frame);
        if let color = UIApplication.shared.delegate?.window??.tintColor {
            tintColor = color;
        }
        rootViewController = UIViewController()
        windowLevel = UIWindowLevelAlert + 1;
        makeKeyAndVisible()
    }

    required init?(coder aDecoder: NSCoder) {
        fatalError("init(coder:) has not been implemented")
    }

    deinit{
        //  semaphor.signal();
    }

    func present(_ ctrl:UIViewController, animated:Bool, completion: (()->Void)?){
        rootViewController!.present(ctrl, animated: animated, completion: completion);
    }
}

其他回答

我在我的AppDelegate类中使用了这段代码和一些个人变化

-(UIViewController*)presentingRootViewController
{
    UIViewController *vc = self.window.rootViewController;
    if ([vc isKindOfClass:[UINavigationController class]] ||
        [vc isKindOfClass:[UITabBarController class]])
    {
        // filter nav controller
        vc = [AppDelegate findChildThatIsNotNavController:vc];
        // filter tab controller
        if ([vc isKindOfClass:[UITabBarController class]]) {
            UITabBarController *tbc = ((UITabBarController*)vc);
            if ([tbc viewControllers].count > 0) {
                vc = [tbc viewControllers][tbc.selectedIndex];
                // filter nav controller again
                vc = [AppDelegate findChildThatIsNotNavController:vc];
            }
        }
    }
    return vc;
}
/**
 *   Private helper
 */
+(UIViewController*)findChildThatIsNotNavController:(UIViewController*)vc
{
    if ([vc isKindOfClass:[UINavigationController class]]) {
        if (((UINavigationController *)vc).viewControllers.count > 0) {
            vc = [((UINavigationController *)vc).viewControllers objectAtIndex:0];
        }
    }
    return vc;
}

iOS13场景支持(当使用UIWindowScene时)

import UIKit

private var windows: [String:UIWindow] = [:]

extension UIWindowScene {
    static var focused: UIWindowScene? {
        return UIApplication.shared.connectedScenes
            .first { $0.activationState == .foregroundActive && $0 is UIWindowScene } as? UIWindowScene
    }
}

class StyledAlertController: UIAlertController {

    var wid: String?

    func present(animated: Bool, completion: (() -> Void)?) {

        //let window = UIWindow(frame: UIScreen.main.bounds)
        guard let window = UIWindowScene.focused.map(UIWindow.init(windowScene:)) else {
            return
        }
        window.rootViewController = UIViewController()
        window.windowLevel = .alert + 1
        window.makeKeyAndVisible()
        window.rootViewController!.present(self, animated: animated, completion: completion)

        wid = UUID().uuidString
        windows[wid!] = window
    }

    open override func viewDidDisappear(_ animated: Bool) {
        super.viewDidDisappear(animated)
        if let wid = wid {
            windows[wid] = nil
        }

    }

}

斯威夫特5

我刚刚创建了一个新窗口,并在其中添加了警报视图控制器。

查看类TopViewController:

https://gist.github.com/odnaks/3f3fd0d20f318c6276e76d0f9d7de5a7

我使用它很简单,像UIAlertController:

 let alert = TopAlertController()
 alert.title = "title"
 alert.message = "message"
 alert.addAction(UIAlertAction(title: "Ок", style: .default, handler: { _ in }))
 alert.show()

你可以使用两种方法:

-使用UIAlertView或'UIActionSheet'代替(不推荐,因为它在iOS 8中已弃用,但现在可以使用了)

-记得上次显示的视图控制器。举个例子。

@interface UIViewController (TopController)
+ (UIViewController *)topViewController;
@end

// implementation

#import "UIViewController+TopController.h"
#import <objc/runtime.h>

static __weak UIViewController *_topViewController = nil;

@implementation UIViewController (TopController)

+ (UIViewController *)topViewController {
    UIViewController *vc = _topViewController;
    while (vc.parentViewController) {
        vc = vc.parentViewController;
    }
    return vc;
}

+ (void)load {
    [super load];
    [self swizzleSelector:@selector(viewDidAppear:) withSelector:@selector(myViewDidAppear:)];
    [self swizzleSelector:@selector(viewWillDisappear:) withSelector:@selector(myViewWillDisappear:)];
}

- (void)myViewDidAppear:(BOOL)animated {
    if (_topViewController == nil) {
        _topViewController = self;
    }

    [self myViewDidAppear:animated];
}

- (void)myViewWillDisappear:(BOOL)animated {
    if (_topViewController == self) {
        _topViewController = nil;
    }

    [self myViewWillDisappear:animated];
}

+ (void)swizzleSelector:(SEL)sel1 withSelector:(SEL)sel2
{
    Class class = [self class];

    Method originalMethod = class_getInstanceMethod(class, sel1);
    Method swizzledMethod = class_getInstanceMethod(class, sel2);

    BOOL didAddMethod = class_addMethod(class,
                                        sel1,
                                        method_getImplementation(swizzledMethod),
                                        method_getTypeEncoding(swizzledMethod));

    if (didAddMethod) {
        class_replaceMethod(class,
                            sel2,
                            method_getImplementation(originalMethod),
                            method_getTypeEncoding(originalMethod));
    } else {
        method_exchangeImplementations(originalMethod, swizzledMethod);
    }
}

@end 

用法:

[[UIViewController topViewController] presentViewController:alertController ...];

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)
}