在iphone应用程序中如何在后台调用方法？

我必须从后台调用sentRequest方法。如果sendRequest工作完成了，那么我必须调用iphone中的启动屏幕。我正在这样做，但这在dispatch\u async中无法正常工作。我调用这个CheckForUpdateModel类从后台获取所有值，然后调用view controller。但若我放置断点并显示，那个么它只调用sendrequest方法。它不调用此方法

-(void)connectionDidFinishLoading:(NSURLConnection *)connection pleasehelp me here what is wrong some give me this ans to follow dispatch and my xcode version is4.2
    - (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions { 


                                      [BaseModalcopyDatabaseIfNeeded];
        dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_BACKGROUND, 0), ^{ 
            NSLog(@"pradeep"); // Here you can define your code to execute in  background.}); 

            CheckForUpdatesModal *CFUM = [[CheckForUpdatesModal alloc]init];
            [CFUM sendRequest];
            [CFUM release];


        });

             self.SSView = [[[SplashScreenView alloc] initWithNibName:@"SplashScreenView" bundle:nil] autorelease];          
            self.window.rootViewController = SSView;
           [self.window makeKeyAndVisible];
           return YES;
    }

试试这个：-

 dispatch_queue_t queue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_HIGH, 0ul);

 dispatch_async(queue, ^{
        CheckForUpdatesModal *CFUM = [[CheckForUpdatesModal alloc]init];
        [CFUM sendRequest];
        [CFUM release];

    dispatch_sync(dispatch_get_main_queue(), ^{
       //SHOW UR SPLASH SCREEN HERE
    });
});