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问在应用程序处于后台时启动CLLocationManager位置更新
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Stack Overflow用户

提问于 2016-05-05 00:19:20

回答 1查看 1.7K关注 0票数 12

我正在构建一个应用程序，它使用CoreLocation有两个目的：

第一，监测信标区域。大多数情况下，我们使用的是作为信标的特定硬件设备，我们使用CoreLocation跟踪该信标连接的状态。
其次，当应用程序检测到从信标设备断开连接时，我们希望启动一个GPS进程来定位断开连接的位置。

在大多数情况下，当应用程序处于后台时，信号设备的断开回调就会发生。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。当应用程序处于后台时，iOS似乎不启用位置后台更新，如果-startUpdatingLocation调用发生在后台。

显然，我已经正确配置了背景模式NSLocationAlwaysUsageDescription，将属性_locationManager.allowsBackgroundLocationUpdates设置为YES。

令人惊奇的是:如果我在前台时调用-startUpdatingLocation，然后切换到后台，则在后台时正确地发送位置更新。但是，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，然后继续工作，即使我再次切换到后台应用程序。

有人知道或明白我该怎么做才能解决这个问题吗？还是iOS的一个主要制约因素？由于我的应用程序的要求，我真的需要开始定位更新时，应用程序在后台(在回调的信标，确实退出区域)。

顺便说一句，如果你想复制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视图控制器中即可。记住要启用背景模式，在info.plist键"NSLocationAlwaysUsageDescription“中添加一个描述。

- (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CLLocationManager来跟踪NSLogs委托，看看会发生什么。

谢谢,

ios

background

gps

location

core-location

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回答 1

Stack Overflow用户

发布于 2016-08-17 09:48:30

自从你贴出这个问题以来已经三个月了。你自己已经想出来了吗？

我试用了你的密码。我将一些NSLogs放在AppDelegate委托函数和viewDidLoad中。另外，在AppDelegate类中，我注销了留下的后台时间。

如果在进入后台之前调用了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...
****/

如果在进入后台后调用startUpdatingLocation：

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...
****/

注意剩下的背景时间。如果应用程序在CLLocationManager开始更新位置之前进入后台，则剩下的背景时间为3分钟。我不太确定自己，因为我也有我自己的全球定位系统的背景运行问题，但从这个简短的测试，似乎CLLocationManager必须被调用之前，应用程序进入后台。

下面是我把NSLogs放在这里的地方：

- (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]);

}