后续 NSURLConnections 不触发委托方法

Question

我已经到处寻找这个问题的答案，并且看到了很多类似的问题，但解决方案似乎并不适合我的情况。我对 iOS 开发非常陌生，因此我们将不胜感激。

当前的应用程序希望根据其网站生成的 XML 提要来显示城市中发生的事件。我将事件存储在 plist 中，并在应用程序加载时显式检查新事件。当前流程如下：

• 应用程序启动并创建 NSURLConnection 以检查服务器的时间戳并下载它。
• 检查新下载的时间戳与本地时间戳是否更大。如果是，它会重写包含 plist 的文件并发出需要新事件的通知。

这是第二个 NSURLConnection 似乎没有触发的地方。回调方法本身会触发，但委托方法似乎不会在之后触发。

奇怪的是，如果我同时调用两个连接，而不是一个连接作为另一个连接的结果，它们都会触发并调用委托方法。

以下是一些类的代码，为了清晰起见，删除了一些内容：

应用程序委托：

- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions {    

// Set up analytics account

// Set the tab bar controller as the window's root view controller and display.
self.window.rootViewController = self.tabBarController;
[self.window makeKeyAndVisible];

//Set up listeners for event handling
[[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(timeStampResponse:) name:@"TimeStampResponse" object:nil];    

//Set app loading screen

//Create new OperationQueue, set ActivityIndicator and run TimeStamp Check
parseQueue = [NSOperationQueue new];    
[UIApplication sharedApplication].networkActivityIndicatorVisible = YES;
[self timeStampCheck];  
return YES;
}
-(void)timeStampCheck {
NSLog(@"Time Stamp Check, Creating Connection");
NSURLRequest *timeStampURLRequest = [NSURLRequest requestWithURL:[NSURL URLWithString:kTimeStampURL]];
self.timeStampConnection = [[NSURLConnectionWithTag alloc] initWithRequest:timeStampURLRequest delegate:self startImmediately:YES tag:1];
}

-(void)newEventsNeeded {
NSLog(@"Event File Doesn't Exists or New File Needed, Creating Connection");
NSURLRequest *feedURLRequest = [NSURLRequest requestWithURL:[NSURL URLWithString:kEventFeedURL]];
self.eventsFeedConnection = [[NSURLConnectionWithTag alloc] initWithRequest:feedURLRequest delegate:self startImmediately:YES tag:0];
}

//Callback from DateStampParser
-(void)timeStampResponse:(NSNotification *)notif {
NSString *response = [[notif userInfo] objectForKey:@"TimeStampResponse"];
if ([response isEqualToString:@"NewEvents"]) {
    [self newEventsNeeded];
    self.appLoadingViewController.loadingLabel.text = @"New Events Found...";
} else if ([response isEqualToString:@"NoNewEvents"]){
    [self allEventsLoaded];
}
}

以及 NSURLConnection 委托方法

-(void)connection:(NSURLConnectionWithTag *)connection didFailWithError:(NSError *)error {
if (connection.tag == 0) {
    NSLog(@"Connection failed on Event Feed");
} else if (connection.tag == 1) {
    NSLog(@"Connection failed on Time Stamp Check");
}
}

-(void)connection:(NSURLConnectionWithTag *)connection didReceiveResponse:(NSURLResponse *)response{
NSHTTPURLResponse *httpResponse = (NSHTTPURLResponse *)response;
NSLog(@"connection:didRecieveResponse:NSHTTPURLResponse");
if ((([httpResponse statusCode]/100) == 2)) {
    //Handling for eventsFeedConnection
    if (connection.tag == 0) {

        NSLog(@"Connection tag = 0");
        self.eventsData = [NSMutableData data];

    } else if (connection.tag == 1) {

        NSLog(@"Connection tag = 1");
        //NSLog(@"Timestamp connection received response");
        self.timeStampData = [NSMutableData data];

    } 

} else {
    UIAlertView *alert = [[UIAlertView alloc] initWithTitle:@"Network Error" message:@"No Response from the Server" delegate:nil cancelButtonTitle:@"Ok" otherButtonTitles:nil];
    [alert show];
    [alert release];
}
}

-(void)connection:(NSURLConnectionWithTag *)connection didReceiveData:(NSData *)data{
//Handling for eventsFeedConnection
if (connection.tag == 0) {

    self.appLoadingViewController.loadingLabel.text = @"Downloading Events...";
    [eventsData appendData:data];

} else if (connection.tag == 1) {

    self.appLoadingViewController.loadingLabel.text =@"Checking for New Events...";
    [timeStampData appendData:data];

}   
}

-(void)connectionDidFinishLoading:(NSURLConnectionWithTag *)connection{
//Handling for eventsFeedConnection
if (connection.tag == 0) {

    NSLog(@"EventFeed Connection Finished");
    self.eventsFeedConnection = nil;
    [eventsFeedConnection release];
    ParserOperation *parser = [[ParserOperation alloc] initWithData:self.eventsData];
    [parseQueue addOperation:parser];
    [parser release];
    self.eventsData = nil;
    //[eventCategoryListViewController reenableRefreshButton];

} else if (connection.tag ==1){

    NSLog(@"TimeStamp Connection Finished");
    self.timeStampConnection = nil;
    [timeStampConnection release];
    DateStampParser *parser = [[DateStampParser alloc] initWithData:self.timeStampData];
    [parseQueue addOperation:parser];
    [parser release];
    self.timeStampData = nil;

} 

}

不确定仅此而已是否显而易见代码或问题是什么，但如果需要任何额外的代码/需要澄清我想要完成的任务，请告诉我。

感谢

为了清晰起见进行编辑 只是为了澄清，来自 newEventsNeeded 的 NSLog 被触发，但只有委托方法不会被触发。

Answer 1

确保启动 NSURLConnection 的线程有一个运行循环。 NSURLConnection 的异步回调被分派到调用线程的运行循环上。如果调用线程（在本例中，它似乎是一个 NSOperation 队列）没有运行循环，或者它没有在默认运行循环模式下运行，那么您将看不到任何委托回调。您第一次调用 [self timeStampCheck] 是在主线程上，所以没关系。您后面的调用来自操作队列，该队列可能没有运行循环。

文档中的相关片段：

委托

连接的委托对象。代表将收到
随着加载的进行委托消息。给代表的消息
将在调用此方法的线程上发送。用于连接
为了正确工作，调用线程的运行循环必须运行在
默认运行循环模式。