iOS 7 Programming Cookbook

11.2. Handling Timeouts in Asynchronous Connections

Problem

You want to set a wait limit—in other words, a timeout—on an asynchronous connection.

Solution

Set the timeout on the URL request that you pass to the NSURLConnection class.

Discussion

When instantiating an object of type NSURLRequest to pass to your URL connection, you can use its requestWithURL:cachePolicy:timeoutInterval: class method and pass the desired number of seconds of your timeout as the timeoutInterval parameter.

For instance, if you want to wait a maximum of 30 seconds to download the contents of Apple’s home page using a synchronous connection, create your URL request like so:

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

    NSString *urlAsString = @"http://www.apple.com";
    NSURL *url = [NSURL URLWithString:urlAsString];

    NSURLRequest *urlRequest =
    [NSURLRequest
     requestWithURL:url
     cachePolicy:NSURLRequestReloadIgnoringLocalAndRemoteCacheData
     timeoutInterval:30.0f];

    NSOperationQueue *queue = [[NSOperationQueue alloc] init];

    [NSURLConnection
     sendAsynchronousRequest:urlRequest
     queue:queue
     completionHandler:^(NSURLResponse *response,
                         NSData *data,
                         NSError *error) {

         if ([data length] >0  && error == nil){
             NSString *html =
             [[NSString alloc] initWithData:data
                                   encoding:NSUTF8StringEncoding];
             NSLog(@"HTML = %@", html);
         }
         else if ([data length] == 0 && error == nil){
             NSLog(@"Nothing was downloaded.");
         }
         else if (error != nil){
             NSLog(@"Error happened = %@", error); ...