IOS dispatch_get_main_queue（）被调用多次

Question

我测试的互联网连接与Reachability和dispatch_async(dispatch_get_main_queue() 当我测试下面的代码，它的工作原理，但它被称为多次。

家长：

@protocol RootViewDelegate <NSObject> 
@optional 
-(void)internetIsDownGoToRoot; 
@end 
- (void)testInternetConnection 
{ 
    internetReachableFoo = [ReachabilityTony reachabilityWithHostname:@"www.google.com"]; 

    __weak typeof(self) weakSelf = self; 
    // Internet is reachable 
    internetReachableFoo.reachableBlock = ^(ReachabilityTony *reach) 
    { 
     // Update the UI on the main thread 
     dispatch_async(dispatch_get_main_queue(), ^{ 
      NSLog(@"Yayyy, we have the interwebs!"); 
      [weakSelf sendLoginRequest]; 
     }); 
    }; 
     // Internet is not reachable 
internetReachableFoo.unreachableBlock = ^(ReachabilityTony *reach) 
{ 
    // Update the UI on the main thread 
    dispatch_async(dispatch_get_main_queue(), ^{ 
     NSLog(@"Someone broke the internet :("); 
     CloudConnection *sharedInstance=[CloudConnection sharedInstance]; 
     sharedInstance.isUserLoggedIN=NO; 
     //update login button 
     [weakSelf updateButtons]; 
     [weakSelf notifyChild]; 

    }); 
}; 
    [internetReachableFoo startNotifier]; 
} 
-(void)viewDidAppear:(BOOL)animated 
{ 
[self testInternetConnection]; 
} 
-(void)viewWillDisappear:(BOOL)animated 
{ 
    internetReachableFoo= nil; 

} 
//notify childs no connection come back to root 
-(void) notifyChild 
{ 
    [delegate internetIsDownGoToRoot]; 

} 

儿童：

-(void)viewDidAppear:(BOOL)animated 
{ 

    NSArray *viewControllers =  self.navigationController.viewControllers; 
    int count = [viewControllers count]; 
    id previousController = [viewControllers objectAtIndex:count - 2]; 
    RootViewController *rvc= previousController; 
    rvc.delegate=self; 


} 

-(void)internetIsDownGoToRoot 
{ 
    //internet connection is no avaliable go to root 
    [self.navigationController popToRootViewControllerAnimated:YES]; 

} 

所以这是parentview可以说我推抵扣childview 5倍和关闭互联网。我看到的NSLog是

Someone broke the internet :(
Someone broke the internet :(
Someone broke the internet :(
Someone broke the internet :(
Someone broke the internet :(

，你可以看到我已经加入internetReachableFoo= nil;但我并没有改变任何东西。

请告诉我上面的代码，为什么它被称为多次回事？

什么是使用此块可能发生的危险？

Answer 1

它被称为多次，因为每次你弹出孩子，根获得-viewDidAppear:并调用-testInternetConnection，它重新运行可达性测试。

更新：确定你已经略有改变你的问题。为什么你得到5“消失”的消息是因为你永远不会停止通知。只要它在运行，可达性就会保持自己的活力，因此扼杀你的参考并不会消灭它。在清除它之前，您需要明确地说出[internetReachableFoo stopNotifier]。