如何让我的计时器在后台运行,然后发送本地通知？

Question

由于某种原因,我的计时器只在前台运行.我在这里寻找解决方案,但我找不到任何好的解决方案.我的计时器使用Core Data,每次减量后都会保存timeInterval.此外,我发送UILocalNotification,但这不起作用.我假设它不发送警报视图,如果它在前台..这就是我现在拥有的:

-(IBAction)startTimer:(id)sender{
    if (timer == nil) {
        [startButton setTitle:@"Pause" forState:UIControlStateNormal];
       timer = [NSTimer scheduledTimerWithTimeInterval:1.0 target:self selector:@selector(timerAction:) userInfo:nil repeats:YES];
    } else {
        [startButton setTitle:@"Resume" forState:UIControlStateNormal];
        [timer invalidate];
        timer = nil;
    }

}
-(void)timerAction:(NSTimer *)t
{
    if(testTask.timeInterval == 0)
    {
        if (self.timer)
        {
            [self timerExpired];
            [self.timer invalidate];
            self.timer = nil;
        }
    }
    else
    {
        testTask.timeInterval--;
        NSError *error;
        if (![self.context save:&error]) {
            NSLog(@"couldn't save: %@", [error localizedDescription]);
        }
    }
    NSUInteger seconds = (NSUInteger)round(testTask.timeInterval);
    NSString *string = [NSString stringWithFormat:@"%02u:%02u:%02u",
                        seconds / 3600, (seconds / 60) % 60, seconds % 60];
    timerLabel.text = string;
    NSLog(@"%f", testTask.timeInterval);
}
-(void)timerExpired{
    UILocalNotification* localNotification = [[UILocalNotification alloc] init];
    localNotification.alertBody = @"Time is up";
    localNotification.alertAction = @"Ok";
    localNotification.timeZone = [NSTimeZone defaultTimeZone];
    [[UIApplication sharedApplication]presentLocalNotificationNow:localNotification];
}

我非常感谢让我的计时器在后台运行的一些指导(就像Apple的计时器一样).我不确定如何使用NSDateComponents,因为即使应用程序在后台我也需要更新testTask.timeInterval.

Answer 1

UIBackgroundTaskIdentifier bgTask =0;
UIApplication  *app = [UIApplication sharedApplication];
bgTask = [app beginBackgroundTaskWithExpirationHandler:^{
    [app endBackgroundTask:bgTask];
}];

NSTimer *timer = [NSTimer scheduledTimerWithTimeInterval:1.0
           target:self
           selector:@selector(timerCountDown:)
           userInfo:nil
           repeats:YES];

现在使用此方法来触发通知.计时器将在后台运行.