IOS dispatch_get_main_queue()被多次调用

Question

我使用 Reachability 和 dispatch_async(dispatch_get_main_queue() 测试互联网连接当我测试以下代码时，它可以正常工作，但会被多次调用。

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];

}

child :

-(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 让我说我 push-pop childview 5 次并关闭互联网。我在 nslog 上看到

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

如您所见，我添加了 internetReachableFoo= nil; 但我没有更改任何内容。

上面的代码是怎么回事，为什么会被多次调用？

使用这个 block 可能有什么危险？

Answer 1

它会被多次调用，因为每次弹出子节点时，根节点都会获取 -viewDidAppear: 并调用 -testInternetConnection，这会重新运行可达性测试。

更新:好的，您已经稍微更改了您的问题。您收到 5 条“确实消失”消息的原因是因为您从不停止通知程序。只要它正在运行，可达性就会使自己保持事件状态，因此清除您的引用并不会杀死它。你需要明确地说出 [internetReachableFoo stopNotifier]，然后再将其删除。