标签：des style blog io os ar div sp cti
步骤：
1.在info.plist里加入UIBackgroundModes键，其值为数组，数组之一为voip字符串：
<key>UIBackgroundModes</key><array><string>voip</string></array>
2.在程序启动的时候调用- (void)setupBackgroundHandler函数，函数体如下：
#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]; }} |
解说：
- (BOOL)setKeepAliveTimeout:(NSTimeInterval)timeout handler:(void (^)(void))keepAliveHandler
函数功能：app每隔timeout唤醒一次。
0.要成功调用该函数，就必须在Info.plist里设UIBackgroundModes键的array值之一voip字符串.
1.timeout必须>=600
2.唤醒app的时间间隔是不精准的。
3.唤醒后只有10秒执行时间。即handler里的代码要在10秒类执行完。10秒后app再次被阻塞。
（可以用-backgroundTimeRemaining属性来返回剩余时间）
4.该函数成功调用后，在程序生命周期内有效。
该函数的效果在回到前台的状况下,依然有效。（因此可以把它当timer使.）
5.clearKeepAliveTimeout函数用来清除handler。
标签：des style blog io os ar div sp cti
原文地址：http://www.cnblogs.com/wudan7/p/3967909.html
