Question

我一直在寻找这个问题的答案并且看到了很多类似的问题，但解决方案似乎与我的情况无关。我对iOS开发很新，所以任何帮助都会受到赞赏。

当前应用程序希望根据其网站生成的XML Feed显示城市中发生的事件。我将事件存储在plist中并在app load上明确检查新事件。目前的流程如下：

应用程序启动并生成NSURLConnection以检查服务器的时间戳并下载。
检查新下载的时间戳与本地时间戳，以查看它是否更大。如果是，则重写包含plist的文件并触发需要新事件的通知。

这是第二个NSURLConnection似乎没有触发的地方。回调方法本身会触发，但看起来似乎不会触发委托方法。

奇怪的是，如果我同时调用两个连接，而不是另一个连接，则它们都将触发并调用委托方法。

以下是一些类的代码，为清楚起见删除了一些内容：

申请代表：

- (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];
}
}

和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;

} 

}

不确定这段代码是否显而易见，或者问题是什么，但是如果需要任何额外的代码/需要澄清我想要完成的事情，请告诉我。

由于

为了清晰起见，

编辑只是为了澄清，来自newEventsNeeded的NSLog会引发火灾，但只是委托方法不会被解雇。

Answer 1

确保启动NSURLConnection的线程有一个runloop。 NSURLConnection的异步回调被分派到调用线程runloop上。如果调用线程（在这种情况下，它似乎是NSOperation队列）没有runloop，或者它没有在默认的运行循环模式下运行，则不会看到任何委托回调。您对[self timeStampCheck]的第一次调用是在主线程上，所以没关系。您以后的调用来自操作队列，可能没有runloop。

来自the documentation的相关摘录：

委托

连接的委托对象。代表将收到   在负载进行时委派消息。给代表的消息   将在调用此方法的线程上发送。用于连接   要正常工作，调用线程的运行循环必须在运行   默认的运行循环模式。

后续NSURLConnections未触发委托方法

1 个答案: