进入后台状态时取消UIAlertViews

我很好奇 Dad's answer (有趣的用户名:),很好奇为什么会被否决。

下面是UIAlertView子类的.m部分。

编辑: (Cdric)我添加了一种方法来捕获对委托方法的调用,然后删除观察者,以避免多次注册到通知中心。

在这个github repo中捆绑在一个类中的所有内容: https://github.com/sdarlington/WSLViewAutoDismiss

    #import "UIAlertViewAutoDismiss.h"
    #import <objc/runtime.h>

    @interface UIAlertViewAutoDismiss () <UIAlertViewDelegate> {
        id<UIAlertViewDelegate> __unsafe_unretained privateDelegate;
    }
    @end

    @implementation UIAlertViewAutoDismiss

    - (id)initWithTitle:(NSString *)title
                message:(NSString *)message
               delegate:(id)delegate
      cancelButtonTitle:(NSString *)cancelButtonTitle
      otherButtonTitles:(NSString *)otherButtonTitles, ...
    {
        self = [super initWithTitle:title
                            message:message
                           delegate:self
                  cancelButtonTitle:cancelButtonTitle
                  otherButtonTitles:nil, nil];

        if (self) {
            va_list args;
            va_start(args, otherButtonTitles);
            for (NSString *anOtherButtonTitle = otherButtonTitles; anOtherButtonTitle != nil; anOtherButtonTitle = va_arg(args, NSString *)) {
                [self addButtonWithTitle:anOtherButtonTitle];
            }
            privateDelegate = delegate;
        }
        return self;
    }

    - (void)dealloc
    {
        privateDelegate = nil;
        [[NSNotificationCenter defaultCenter] removeObserver:self name:UIApplicationDidEnterBackgroundNotification object:nil];
        [super dealloc];
    }

    - (void)setDelegate:(id)delegate
    {
        privateDelegate = delegate;
    }

    - (id)delegate
    {
        return privateDelegate;
    }

    - (void)show
    {
        [[NSNotificationCenter defaultCenter] addObserver:self
                                                 selector:@selector(applicationDidEnterBackground:)
                                                     name:UIApplicationDidEnterBackgroundNotification
                                                   object:nil];

        [super show];
    }

    - (void)applicationDidEnterBackground:(NSNotification *)notification
    {
        [super dismissWithClickedButtonIndex:[self cancelButtonIndex] animated:NO];
        [[NSNotificationCenter defaultCenter] removeObserver:self name:UIApplicationDidEnterBackgroundNotification object:nil];
    }

    #pragma mark - UIAlertViewDelegate

    // The code below avoids to re-implement all protocol methods to forward to the real delegate.

    - (id)forwardingTargetForSelector:(SEL)aSelector
    {
        struct objc_method_description hasMethod = protocol_getMethodDescription(@protocol(UIAlertViewDelegate), aSelector, NO, YES);
        if (hasMethod.name != NULL) {
            // The method is that of the UIAlertViewDelegate.

            if (aSelector == @selector(alertView:didDismissWithButtonIndex:) ||
                aSelector == @selector(alertView:clickedButtonAtIndex:))
            {
                [[NSNotificationCenter defaultCenter] removeObserver:self
                                                                name:UIApplicationDidEnterBackgroundNotification
                                                              object:nil];
            }
            return privateDelegate;
        }
        else {
            return [super forwardingTargetForSelector:aSelector];
        }
    }

    @end

这很好,因为您可以像使用UIAlertView一样开始使用它。

我还没来得及彻底测试它,但我没有注意到任何副作用。

- (void) hide {
  [self dismissWithClickedButtonIndex:0 animated:YES];
}

和托付给 UIApplicationWillResignActiveNotification

[[NSNotificationCenter defaultCenter] addObserver:alertView selector:@selector(hide) name:@"UIApplicationWillResignActiveNotification" object:nil];

一种完全不同的方法是递归搜索。

应用程序委托的递归函数

- (void)checkViews:(NSArray *)subviews {
    Class AVClass = [UIAlertView class];
    Class ASClass = [UIActionSheet class];
    for (UIView * subview in subviews){
        if ([subview isKindOfClass:AVClass]){
            [(UIAlertView *)subview dismissWithClickedButtonIndex:[(UIAlertView *)subview cancelButtonIndex] animated:NO];
        } else if ([subview isKindOfClass:ASClass]){
            [(UIActionSheet *)subview dismissWithClickedButtonIndex:[(UIActionSheet *)subview cancelButtonIndex] animated:NO];
        } else {
            [self checkViews:subview.subviews];
        }
    }
}

[self checkViews:application.windows];

呵呵。我还没有尝试过这个,但是我想知道创建一个UIAlertView的子类是否有意义,它可以监听这个通知并关闭它自己,如果是这样的话。。。

正如有人在评论中提到的:接受的答案并不是自ios4.0以来最好/最干净的答案,因为我们有块!我是这样做的:

UIAlertView* alert = [[UIAlertView alloc] initWithTitle:@"Alert!" message:@"This alert will dismiss when application resigns active!" delegate:self cancelButtonTitle:@"OK" otherButtonTitles:nil];
[alert show];
[[NSNotificationCenter defaultCenter] addObserverForName:UIApplicationWillResignActiveNotification object:nil queue:[NSOperationQueue mainQueue] usingBlock:^(NSNotification* notification){
        [alert dismissWithClickedButtonIndex:0 animated:NO];
    }];

UIAlertController类旨在按原样使用,不支持子类化。此类的视图层次结构是私有的,不能修改。

applicationDidEnterBackground

试试这个(用Swift):

extension UIApplication
{
    class func dismissOpenAlerts(base: UIViewController? = UIApplication.sharedApplication().keyWindow?.rootViewController)
    {
        //If it's an alert, dismiss it
        if let alertController = base as? UIAlertController
        {
            alertController.dismissViewControllerAnimated(false, completion: nil)
        }

        //Check all children
        if base != nil
        {
            for controller in base!.childViewControllers
            {
                if let alertController = controller as? UIAlertController
                {
                    alertController.dismissViewControllerAnimated(false, completion: nil)
                }
            }
        }

        //Traverse the view controller tree
        if let nav = base as? UINavigationController
        {
           dismissOpenAlerts(nav.visibleViewController)
        }
        else if let tab = base as? UITabBarController, let selected = tab.selectedViewController
        {
           dismissOpenAlerts(selected)
        }
        else if let presented = base?.presentedViewController
        {
           dismissOpenAlerts(presented)
        }
    }
}

然后在AppDelegate中:

func applicationDidEnterBackground(application: UIApplication)
{
    UIApplication.dismissOpenAlerts()
}

我用以下代码解决了这个问题:

/* taken from the post above (Cédric)*/
- (void)checkViews:(NSArray *)subviews {
    Class AVClass = [UIAlertView class];
    Class ASClass = [UIActionSheet class];
    for (UIView * subview in subviews){
        NSLog(@"Class %@", [subview class]);
        if ([subview isKindOfClass:AVClass]){
            [(UIAlertView *)subview dismissWithClickedButtonIndex:[(UIAlertView *)subview cancelButtonIndex] animated:NO];
        } else if ([subview isKindOfClass:ASClass]){
            [(UIActionSheet *)subview dismissWithClickedButtonIndex:[(UIActionSheet *)subview cancelButtonIndex] animated:NO];
        } else {
            [self checkViews:subview.subviews];
        }
    }
}



/*go to background delegate*/
- (void)applicationDidEnterBackground:(UIApplication *)application
{
    for (UIWindow* window in [UIApplication sharedApplication].windows) {
        NSArray* subviews = window.subviews;
        [self checkViews:subviews];
    }
}

最简单的方法是保存对UIAlertView的引用,这样就可以取消它。当然,正如petert提到的,您可以通过通知来完成,或者在UIApplication上使用delegate方法

applicationWillResignActive:

因此,当您真正进入后台时,我会关闭UIAlertView并在委托调用中保存状态:

applicationDidEnterBackground:

在developer.apple.com上免费查看会话105-在WWDC10的iOS4上采用多任务处理。16:00开始变得有趣

graphic 了解应用程序的不同状态

UIApplicationWillResignActiveNotification (请参阅UIApplication)在具有UIAlertView之类内容的视图中,您可以通过以下方式以编程方式删除警报视图:

(void)dismissWithClickedButtonIndex:(NSInteger)buttonIndex animated:(BOOL)animated

对这个方法的讨论甚至暗示了它在iOS4中的用途!

在iPhoneOS4.0中,当应用程序移到后台时,您可能希望调用此方法。当应用程序移到后台时,不会自动取消警报视图。此行为与以前版本的操作系统不同,以前版本的操作系统在应用程序终止时自动取消。解除警报视图使应用程序有机会保存更改或中止操作,并执行任何必要的清理,以防以后终止应用程序。

assign

@property (nonatomic, assign) UIAlertView* alertview;

然后,在app delegate中:

[self.viewController.alertview dismissWithClickedButtonIndex:[self.viewController.alertview cancelButtonIndex] animated:NO];

你可以把这个放进去 applicationDidEnterBackground: 或者任何你认为合适的地方。它在应用程序退出时以编程方式关闭警报。我一直在这样做,效果很好。

在UIAlert视图上创建类别

使用 http://nshipster.com/method-swizzling/

- 如果要删除所有数据,请对已保存的警报视图调用dissible并清空数组。

另一种解决方案,基于普克尔的, answer ,当应用程序放在后台时,观察者将被移除。如果用户通过按下一个按钮来解除警报,观察者仍将处于活动状态,但只有在将应用程序放在后台(在后台运行程序块时,显示“nil alertView”,并移除观察者)时才会激活。

    UIAlertView *alert = [[UIAlertView alloc] initWithTitle:title
                                                message:message
                                               delegate:alertDelegate
                                      cancelButtonTitle:cancelButtonText
                                      otherButtonTitles:okButtonText, nil];
   [alert show];

   __weak UIAlertView *weakAlert = alert;
   __block __weak id observer = [[NSNotificationCenter defaultCenter] addObserverForName:UIApplicationWillResignActiveNotification object:nil queue:      [NSOperationQueue mainQueue] usingBlock:^(NSNotification* notification){
   [weakAlert dismissWithClickedButtonIndex:[weakAlert cancelButtonIndex] animated:NO];
   [[NSNotificationCenter defaultCenter] removeObserver:observer];
    observer = nil;
   }];