iOS 后台执行

- (void)applicationDidEnterBackground:(UIApplication *)application  
{  
    // Use this method to release shared resources, save user data, invalidate timers, and store enough application state information to restore your application to its current state in case it is terminated later.   
    // If your application supports background execution, this method is called instead of applicationWillTerminate: when the user quits.  
      
    UIDevice *device = [UIDevicecurrentDevice];  
    BOOL backgroundSupported = NO;  
    if ([device respondsToSelector:@selector(isMultitaskingSupported)]) {  
        backgroundSupported = YES;  
    }  
      
    __blockUIBackgroundTaskIdentifier bgTaskId = [application beginBackgroundTaskWithExpirationHandler:^{  
        [application endBackgroundTask:bgTaskId];  
        bgTaskId = UIBackgroundTaskInvalid;  
    }];  
      
    if (backgroundSupported) {  
        dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{  
            //  
        });  
    }  ?

#pragma mark - VoIP
 
- (void)setupBackgroundHandler
{   
    if( UIUDeviceIsBackgroundSupported() )
    {
        if(
           [[UIApplication sharedApplication] setKeepAliveTimeout:600 handler: ^
            {
                [self requestServerHowManyUnreadMessages];
            }
            ]
           )
        {
            UDLog(@"Set Background handler successed!");
        }
        else
        {//failed
            UDLog(@"Set Background handler failed!");
        }
    }
    else
    {
        UDLog(@"This Deviece is not Background supported.");
    }
}
 
- (void)requestServerHowManyUnreadMessages
{
    UIApplication* app = [UIApplication sharedApplication];
     
    if([app applicationState] == UIApplicationStateBackground)
    {
        NSArray * oldNotifications = [app scheduledLocalNotifications];
        if ([oldNotifications count] > 0)
            [app cancelAllLocalNotifications];
        UILocalNotification* alarm = [[[UILocalNotification alloc] init] autorelease];
        if (alarm)
        {
            alarm.fireDate = [NSDate dateWithTimeIntervalSinceNow:15];
            alarm.timeZone = [NSTimeZone defaultTimeZone];
            alarm.repeatInterval = 0;
            alarm.soundName = UILocalNotificationDefaultSoundName;
            alarm.alertBody = @"Time to request MOA2 Server!";
            [app scheduleLocalNotification:alarm];
        }
    }
    else if([app applicationState] == UIApplicationStateActive)
    {
        UIAlertView *alertView =  [[[UIAlertView alloc] init] autorelease];
        [alertView setTitle:@"alert"];
        [alertView setMessage:@"Time to request MOA2 Server!"];
        [alertView addButtonWithTitle:NSLocalizedString(@"cancel", nil)];
        [alertView setDelegate:nil];
        [alertView show];
    }
}