iOS NSNotificationCenter Observer 未被删除 [英] iOS NSNotificationCenter Observer not being removed

问题描述

我在 AppDelegate 中有以下代码.目的是创建几个观察者，然后调用一些代码.一旦该代码完成，它就会发布一个通知，然后观察者应该移除两个观察者并调用完成处理程序.

I have the following code within AppDelegate. The purpose being to create a couple of observers, and then call some code. Once that code completes it then posts a notification, and the observer should then remove both observers and call the completion handler.

我的问题是观察者似乎没有像我预期的那样被移除.发布通知，并将 NSLog 条目写入控制台，因此我知道观察者正在工作.但是，在第二次调用时，NSLog 被调用了两次，第三次调用了 3 次，以此类推.

My issue is that it appears that the observers are not being removed as I expected. The notification is posted, and the NSLog entry is written to console, so I know that the observer is working. However, on the second time of calling, the NSLog is called twice, third time three times etc.

我的想法是，这与从观察者运行的代码块中删除有关，但是，我不确定如何解决此问题(如果确实是问题所在).

My thoughts are that this is to do with the removal being within the block of code that is running from the observer, however, I am unsure how I can resolve this (if indeed this is what the issue is).

有人能解释一下我是如何做到这一点的吗?

Could someone be so kind as to explain how I can achieve this?

谢谢.

-(void) application:(UIApplication *)application performFetchWithCompletionHandler:
(void (^)(UIBackgroundFetchResult))completionHandler {

    [[NSNotificationCenter defaultCenter] addObserverForName:@"fetchDidCompleteNewData" object:nil
                                                     queue:nil usingBlock:^(NSNotification *completed) {

                                                         //Remove Observers
                                                         [[NSNotificationCenter defaultCenter] removeObserver:self
                                                                                                         name:@"fetchDidCompleteNewData"
                                                                                                       object:nil];
                                                         [[NSNotificationCenter defaultCenter] removeObserver:self
                                                                                                         name:@"fetchDidCompleteNoData"
                                                                                                       object:nil];


                                                         // Post completion
                                                         completionHandler(UIBackgroundFetchResultNewData);
                                                         NSLog(@"Background fetch completed... New Data");
                                                     }];

    [[NSNotificationCenter defaultCenter] addObserverForName:@"fetchDidCompleteNoData" object:nil
                                                       queue:nil usingBlock:^(NSNotification *completed) {

                                                           //Remove Observers
                                                           [[NSNotificationCenter defaultCenter] removeObserver:self
                                                                                                           name:@"fetchDidCompleteNoData"
                                                                                                         object:nil];

                                                           [[NSNotificationCenter defaultCenter] removeObserver:self
                                                                                                           name:@"fetchDidCompleteNewData"
                                                                                                         object:nil];

                                                           //post completion
                                                           completionHandler(UIBackgroundFetchResultNoData);
                                                           NSLog(@"Background fetch completed... No New Data");

                                                       }];

    GetDetails *getDetails = [[GetDetails alloc] init];
    [getDetails backgroundRefresh];

}

- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions
{
    [[UIApplication sharedApplication] setMinimumBackgroundFetchInterval:UIApplicationBackgroundFetchIntervalMinimum];

    return YES;
}

推荐答案

您没有将 self 注册为对象.此外，当块被 addObserverForName: 压入堆栈时，该方法尚未返回，因此 notification 为 nil.

You are not registering self as an object. Moreover, when the block is pushed onto the stack by addObserverForName: the method has not yet returned so the notification is nil.

使用block创建一个全局对象，例如

Make a global object using block, eg

__block __weak id notification;

那么，

notification =  [[NSNotificationCenter defaultCenter] addObserverForName:@"fetchDidCompleteNewData" object:nil queue:nil usingBlock:^(NSNotification *completed) {

   //Remove Observers
   [[NSNotificationCenter defaultCenter] removeObserver:notification];
}];

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