Question

我想在每次收到位置更新时我的应用在后台时计算到目的地的路线。

但是，[MKDirections calculateDirectionsWithCompletionHandler]是一个异步调用，因此我的问题是：如果在我的应用收到位置更新后需要超过5秒才完成，我的应用会被终止吗？您的建议是什么，以确保此请求有足够的时间完成？

Answer 1

为了请求额外的时间让您的应用在后台运行以完成其任务（异步或非异常），您可以使用beginBackgroundTaskWithExpirationHandler:。

例如：

- (void)locationManager:(CLLocationManager *)manager didUpdateToLocation:(CLLocation *)newLocation fromLocation:(CLLocation *)oldLocation {

    // If the application is in the background...
    if([[UIApplication sharedApplication] applicationState] != UIApplicationStateActive) {

        // Create the beginBackgroundTaskWithExpirationHandler
        // which will execute once your task is complete
        bgTask = [[UIApplication sharedApplication] beginBackgroundTaskWithExpirationHandler:^{
            // Clean up any unfinished task business by marking where you
            // stopped or ending the task outright.
            [application endBackgroundTask:bgTask];
            bgTask = UIBackgroundTaskInvalid;
        }];

        // Start the long-running task and return immediately.
        dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{

            NSMutableDictionary *dict = [[NSMutableDictionary alloc] init];
            [dict setObject:application forKey:@"application"];

            // Start a timer to keep the program alive for 180 seconds max
            // (less if that's all that's necessary)
            [NSTimer scheduledTimerWithTimeInterval:180 target:self selector:@selector(delayMethod:) userInfo:nil repeats:NO];

        });

    }

    // ... the rest of your didUpdateToLocation: code ...

}

- (void)delayMethod:(NSTimer*)timer {

    // End the background task you created with beginBackgroundTaskWithExpirationHandler
    [[[timer userInfo] objectForKey:@"application"] endBackgroundTask:bgTask];
    bgTask = UIBackgroundTaskInvalid;
}

当app在后台时，MKDirections会计算方向

1 个答案: