iOS 後台執行

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轉自：http://blog.csdn.net/yujianxiang666/article/details/35996005

當App進入到後台時，可以有一段時間做處理工作。

或者，對於某些服務，可以長時間運行，比如播放音樂。

?

對於長時間啟動並執行任務，需要在Info.plist添加一行，鍵為UIBackgroundModes，值為一個數組，可以包含如下幾個字串：

• audio
• location
• voip
• newsstand-content
• external-accessory
• bluetooth-central

?

然後，在後台就可以做一些事情了

- (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), ^{              //          });      }  ?

}?

步驟：

1.在info.plist裡加入UIBackgroundModes鍵，其值為數組，數組之一為voip字串：

<key>UIBackgroundModes</key><array><string>voip</string></array>

2.在程式啟動的時候調用- (void)setupBackgroundHandler函數，函數體如下：

?

?

#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];    }}

?

解說：

- (BOOL)setKeepAliveTimeout:(NSTimeInterval)timeout?handler:(void (^)(void))keepAliveHandler

函數功能：app每隔timeout喚醒一次。

0.要成功調用該函數，就必須在Info.plist裡設UIBackgroundModes鍵的array值之一voip字串.

1.timeout必須>=600

2.喚醒app的時間間隔是不精準的。

3.喚醒後只有10秒執行時間。即handler裡的代碼要在10秒類執行完。10秒後app再次被阻塞。

（可以用-backgroundTimeRemaining屬性來返回剩餘時間）

4.該函數成功調用後，在程式生命週期內有效。

該函數的效果在回到前台的狀況下,依然有效。（因此可以把它當timer使.）?

5.clearKeepAliveTimeout函數用來清除handler。

iOS 後台執行