- (void)timerAction:(NSTimer *)timer {    count++;    UILabel *lable = (UILabel *)[self.window viewWithTag:100];    NSString *str = [NSString stringWithFormat:@"%d", count];    lable.text = str;    if (count % 200 == 0) {        UIApplication *application = [UIApplication sharedApplication];        [application endBackgroundTask:taskId];        taskId = [application beginBackgroundTaskWithExpirationHandler:NULL];        count = 0;    }    NSLog(@"%@", str);}- (void)applicationDidEnterBackground:(UIApplication *)application{    taskId = [application beginBackgroundTaskWithExpirationHandler:^{        [application endBackgroundTask:taskId];    }];        [NSTimer scheduledTimerWithTimeInterval:1 target:self selector:@selector(timerAction:) userInfo:nil repeats:YES];}// 实际结果，偶然性被kill掉，175秒，300秒，在真机测试中。