ios - 在应用程序处于后台时启动 CLLocationManager 位置更新

Question

我正在构建一个将 CoreLocation 用于两个目的的应用:

1. 首先，监控信标区域。大多数情况下，我们使用充当信标的特定硬件设备，并使用 CoreLocation 跟踪该信标连接的状态。

2. 其次，当应用检测到与信标设备断开连接时，我们想要启动一个 GPS 进程来定位断开连接发生的位置。

在大多数情况下，信标设备的断开回调发生在应用程序处于后台时。因此，应用程序必须在后台调用 -startUpdatingLocation 来启动 GPS 跟踪。

这就是问题所在。如果 -startUpdatingLocation 调用发生在应用程序处于后台时，iOS 似乎不会启用位置后台更新。

显然，我已经正确配置了后台模式，NSLocationAlwaysUsageDescription，将属性 _locationManager.allowsBackgroundLocationUpdates 设置为 YES。

令人惊奇的是:如果我在前台调用 -startUpdatingLocation 然后切换到后台，则在后台时位置更新会正确发送。但是，当在后台调用 -startUpdatingLocation 时，应用程序会收到 2 或 3 个位置更新，然后永远暂停。直到我手动将应用程序带回前台，当位置更新恢复时，然后即使我再次将应用程序切换到后台，也能继续工作。

有人知道或了解我应该怎么做才能解决这个问题吗？还是 iOS 的主要限制？由于我的应用程序的要求，我确实需要在应用程序处于后台时开始定位更新(在信标退出区域的回调内)。

顺便说一句，如果你想重现这个问题是很容易的。只需在 Xcode 中创建一个空白项目并将此代码添加到默认 View Controller 。请记住启用后台模式，将描述添加到您的 info.plist 键“NSLocationAlwaysUsageDescription”。

- (void)viewDidLoad 
{
    [super viewDidLoad];

    _locationManager = [[CLLocationManager alloc] init];

    if (NSFoundationVersionNumber > NSFoundationVersionNumber_iOS_8_3)
        _locationManager.allowsBackgroundLocationUpdates = YES;

    _locationManager.delegate = self;
    _locationManager.activityType = CLActivityTypeOther;
    _locationManager.desiredAccuracy = kCLLocationAccuracyBest;
    _locationManager.distanceFilter = kCLDistanceFilterNone;

    [_locationManager requestAlwaysAuthorization];

    // Creating a background task to delay the start of the startUpdatingLocation
    __block UIBackgroundTaskIdentifier taskIdentifier = UIBackgroundTaskInvalid;
    taskIdentifier = [[UIApplication sharedApplication] beginBackgroundTaskWithExpirationHandler:^{
        [[UIApplication sharedApplication] endBackgroundTask:taskIdentifier];
    }];

    // Delaying the call to startUpdatingLocation 10 seconds, enough time to dismiss the application
    dispatch_after(dispatch_time(DISPATCH_TIME_NOW, (int64_t)(10 * NSEC_PER_SEC)), dispatch_get_main_queue(), ^{
        [_locationManager startUpdatingLocation];
        dispatch_after(dispatch_time(DISPATCH_TIME_NOW, (int64_t)(1.5 * NSEC_PER_SEC)), dispatch_get_main_queue(), ^{
            [[UIApplication sharedApplication] endBackgroundTask:taskIdentifier];
        });
    });
}

然后，通过执行一些 NSLog 来跟踪 CLLocationManager 委托(delegate)，看看会发生什么。

谢谢，

Answer 1

您发布此问题已经 3 个月了。你自己想出来了吗？

我试过你的代码。我在 AppDelegate 委托(delegate)函数和 viewDidLoad 中放置了一些 NSLogs。另外，在 AppDelegate 类中，我注销了后台剩余时间。

如果在进入后台之前调用 startUpdatingLocation:

2016-08-18 01:22:52.355 test background GPS from StackOF[2267:745042] viewDidLoad
2016-08-18 01:22:52.376 test background GPS from StackOF[2267:745042] _locationManager.allowsBackgroundLocationUpdates = YES;
2016-08-18 01:22:52.382 test background GPS from StackOF[2267:745042] _locationManager requestAlwaysAuthorization
2016-08-18 01:22:52.410 test background GPS from StackOF[2267:745042] applicationDidBecomeActive
2016-08-18 01:22:52.469 test background GPS from StackOF[2267:745042] viewDidAppear
2016-08-18 01:23:03.361 test background GPS from StackOF[2267:745042] [_locationManager startUpdatingLocation];
2016-08-18 01:23:03.362 test background GPS from StackOF[2267:745042] start updating location, _locationManager.allowsBackgroundLocationUpdates == YES
2016-08-18 01:23:03.382 test background GPS from StackOF[2267:745042] Lat/Long: <redacted GPS coordinates>, horizontal accuracy: 65.000000
2016-08-18 01:23:03.630 test background GPS from StackOF[2267:745042] Lat/Long: <redacted GPS coordinates>, horizontal accuracy: 1743.000000
2016-08-18 01:23:03.709 test background GPS from StackOF[2267:745042] Lat/Long: <redacted GPS coordinates>, horizontal accuracy: 1743.000000
2016-08-18 01:23:03.716 test background GPS from StackOF[2267:745042] Lat/Long: <redacted GPS coordinates>, horizontal accuracy: 1743.000000
2016-08-18 01:23:03.720 test background GPS from StackOF[2267:745042] Lat/Long: <redacted GPS coordinates>, horizontal accuracy: 1743.000000
2016-08-18 01:23:03.814 test background GPS from StackOF[2267:745042] Lat/Long: <redacted GPS coordinates>, horizontal accuracy: 65.000000
2016-08-18 01:23:05.004 test background GPS from StackOF[2267:745042] inner block [[UIApplication sharedApplication] endBackgroundTask:taskIdentifier];
2016-08-18 01:23:05.005 test background GPS from StackOF[2267:745042] inner block start updating location, _locationManager.allowsBackgroundLocationUpdates == YES
2016-08-18 01:23:08.287 test background GPS from StackOF[2267:745042] applicationDidEnterBackground. Background time left: 179769313486231570814527423731704356798070567525844996598917476803157260780028538760589558632766878171540458953514382464234321326889464182768467546703537516986049910576551282076245490090389328944075868508455133942304583236903222948165808559332123348274797826204144723168738177180919299881250404026184124858368.000000
2016-08-18 01:23:10.319 test background GPS from StackOF[2267:745042] Lat/Long: <redacted GPS coordinates>, horizontal accuracy: 65.000000
2016-08-18 01:23:19.321 test background GPS from StackOF[2267:745042] Lat/Long: <redacted GPS coordinates>, horizontal accuracy: 65.000000
/****
Keep on polling...
****/

如果 startUpdatingLocation 在进入后台后被调用:

2016-08-18 01:34:29.023 test background GPS from StackOF[2285:747132] viewDidLoad
2016-08-18 01:34:29.030 test background GPS from StackOF[2285:747132] _locationManager.allowsBackgroundLocationUpdates = YES;
2016-08-18 01:34:29.033 test background GPS from StackOF[2285:747132] _locationManager requestAlwaysAuthorization
2016-08-18 01:34:29.047 test background GPS from StackOF[2285:747132] applicationDidBecomeActive
2016-08-18 01:34:29.104 test background GPS from StackOF[2285:747132] viewDidAppear
2016-08-18 01:34:31.612 test background GPS from StackOF[2285:747132] applicationDidEnterBackground. Background time left: 179.964144
2016-08-18 01:34:40.004 test background GPS from StackOF[2285:747132] [_locationManager startUpdatingLocation];
2016-08-18 01:34:40.006 test background GPS from StackOF[2285:747132] start updating location, _locationManager.allowsBackgroundLocationUpdates == YES
2016-08-18 01:34:40.290 test background GPS from StackOF[2285:747132] Lat/Long: <redacted GPS coordinates>, horizontal accuracy: 10.000000
2016-08-18 01:34:40.332 test background GPS from StackOF[2285:747132] Lat/Long: <redacted GPS coordinates>, horizontal accuracy: 355.117789
2016-08-18 01:34:40.336 test background GPS from StackOF[2285:747132] Lat/Long: <redacted GPS coordinates>, horizontal accuracy: 355.118536
2016-08-18 01:34:40.493 test background GPS from StackOF[2285:747132] Lat/Long: <redacted GPS coordinates>, horizontal accuracy: 355.141209
2016-08-18 01:34:40.496 test background GPS from StackOF[2285:747132] Lat/Long: <redacted GPS coordinates>, horizontal accuracy: 355.147748
2016-08-18 01:34:40.505 test background GPS from StackOF[2285:747132] Lat/Long: <redacted GPS coordinates>, horizontal accuracy: 355.148158
2016-08-18 01:34:40.507 test background GPS from StackOF[2285:747132] Lat/Long: <redacted GPS coordinates>, horizontal accuracy: 65.000000
2016-08-18 01:34:41.640 test background GPS from StackOF[2285:747132] inner block [[UIApplication sharedApplication] endBackgroundTask:taskIdentifier];
2016-08-18 01:34:41.642 test background GPS from StackOF[2285:747132] inner block start updating location, _locationManager.allowsBackgroundLocationUpdates == YES
/****
stops polling...
****/

记下后台剩余时间。如果应用程序在 CLLocationManager 开始更新位置之前进入后台，则后台剩余时间为 3 分钟。我自己也不太确定，因为我也有自己的 GPS 后台运行问题，但从这个简短的测试来看，似乎 CLLocationManager 必须在应用程序进入后台之前被调用。

这是我放置 NSLog 的地方:

- (void)viewDidLoad {
    [super viewDidLoad];
    // Do any additional setup after loading the view, typically from a nib.
    NSLog(@"viewDidLoad");

    _locationManager = [[CLLocationManager alloc] init];

    if (NSFoundationVersionNumber > NSFoundationVersionNumber_iOS_8_3)
    {
        _locationManager.allowsBackgroundLocationUpdates = YES;
        NSLog(@"_locationManager.allowsBackgroundLocationUpdates = YES;");
    }



    _locationManager.delegate = self;
    _locationManager.activityType = CLActivityTypeOther;
    _locationManager.desiredAccuracy = kCLLocationAccuracyBestForNavigation;
    _locationManager.distanceFilter = kCLDistanceFilterNone;

    [_locationManager requestAlwaysAuthorization];
    NSLog(@"_locationManager requestAlwaysAuthorization");

    // Creating a background task to delay the start of the startUpdatingLocation
    __block UIBackgroundTaskIdentifier taskIdentifier = UIBackgroundTaskInvalid;
    taskIdentifier = [[UIApplication sharedApplication] beginBackgroundTaskWithExpirationHandler:^{
        [[UIApplication sharedApplication] endBackgroundTask:taskIdentifier];
        NSLog(@"[[UIApplication sharedApplication] endBackgroundTask:taskIdentifier];");
    }];

    // Delaying the call to startUpdatingLocation 10 seconds, enough time to dismiss the application
    dispatch_after(dispatch_time(DISPATCH_TIME_NOW, (int64_t)(10 * NSEC_PER_SEC)), dispatch_get_main_queue(), ^{
        [_locationManager startUpdatingLocation];
        NSLog(@"[_locationManager startUpdatingLocation];");
        if(_locationManager.allowsBackgroundLocationUpdates == YES)
        {
            NSLog(@"start updating location, _locationManager.allowsBackgroundLocationUpdates == YES");
        }
        else
        {
            NSLog(@"start updating location, _locationManager.allowsBackgroundLocationUpdates == NO");
        }
        dispatch_after(dispatch_time(DISPATCH_TIME_NOW, (int64_t)(1.5 * NSEC_PER_SEC)), dispatch_get_main_queue(), ^{
            [[UIApplication sharedApplication] endBackgroundTask:taskIdentifier];
            NSLog(@"inner block [[UIApplication sharedApplication] endBackgroundTask:taskIdentifier];");
            if(_locationManager.allowsBackgroundLocationUpdates == YES)
            {
                NSLog(@"inner block start updating location, _locationManager.allowsBackgroundLocationUpdates == YES");
            }
            else
            {
                NSLog(@"inner block start updating location, _locationManager.allowsBackgroundLocationUpdates == NO");
            }

        });
    });

}

CLLocationManager 委托(delegate)函数:

-(void)locationManager:(CLLocationManager *) manager didUpdateLocations:(nonnull NSArray<CLLocation *> *)locations
{
    CLLocation *location = [locations firstObject];
    NSLog(@"Lat/Long: %f %f, horizontal accuracy: %f",
          location.coordinate.latitude,
          location.coordinate.longitude,
          location.horizontalAccuracy);
}

AppDelegate:

- (void)applicationDidEnterBackground:(UIApplication *)application {

    NSLog(@"applicationDidEnterBackground. Background time left: %f", [[UIApplication sharedApplication] backgroundTimeRemaining]);

}

TL;DR:尝试在 viewDidLoad 或 AppDelegate application:didFinishLaunchingWithOptions: 中调用 startUpdatingLocation/p>