ios - MKDirections 在应用程序处于后台时计算方向

Question

当我的应用程序每次收到位置更新时都在后台运行时，我想计算到达目的地的路线。

但是，[MKDirectionscalculateDirectionsWithCompletionHandler]是一个异步调用，因此我的问题是:如果在我的应用程序收到位置更新后需要超过 5 秒才能完成，我的应用程序是否会终止？为了确保此请求有足够的时间完成，您有何建议？

Answer 1

为了请求额外的时间让您的应用程序在后台运行以完成其任务(异步或非异步)，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;
}