CLLocation 类的课程值一直为 -1。为什么？

Question

我想在用户移动的方向上显示汽车/自行车，因为我使用了 course 属性，但它的值一直是 -1。以下是特定位置的 NSLog 值：

2013-09-09 11:05:09.930 MapApp[143:907] +/- 65.00m（速度 -1.00 mps / 路线 -1.00）@ 09/09/13 11:05 :00 AM 印度标准时间

- (MKAnnotationView *)mapView:(MKMapView *)map viewForAnnotation:(id <MKAnnotation>)annotation
{
    static NSString *AnnotationViewID = @"annotationViewID";

    annotationView = (MKAnnotationView *)[map dequeueReusableAnnotationViewWithIdentifier:AnnotationViewID];

    if (annotationView == nil)
    {
        annotationView = [[[MKAnnotationView alloc] initWithAnnotation:annotation reuseIdentifier:AnnotationViewID] autorelease];
    }
    annotationView.image = [UIImage imageNamed:@"Bike.png"];


    NSLog(@"%@",currentLocation);


    annotationView.transform = CGAffineTransformMakeRotation(45);

    return annotationView;
}

- (void)locationManager:(CLLocationManager *)manager didUpdateToLocation:(CLLocation *)newLocation fromLocation:(CLLocation *)oldLocation
{
    if (newLocation.horizontalAccuracy < 0)
        return;
    if  (!newLocation)
        return;


    currentLocation = newLocation;
    previousLocation = oldLocation;
    if(currentLocation != nil)
    {
        if (myAnnotation)
        {
            [self.myMapView removeAnnotation:myAnnotation];
        }
        CLLocationCoordinate2D location = CLLocationCoordinate2DMake(currentLocation.coordinate.latitude, currentLocation.coordinate.longitude);
        myAnnotation = [[MyAnnotation alloc] initWithCoordinates:location title:@"Current Location" subTitle:nil];
        [self.myMapView addAnnotation:myAnnotation];
    }
}

Answer 1

请参阅此处的文档：

https://developer.apple.com/library/ios/documentation/UserExperience/Conceptual/LocationAwarenessPG/GettingHeadings/GettingHeadings.html#//apple_ref/doc/uid/TP40009497-CH5-SW1

获取设备的航向或路线并非易事，但我能想到的最可能的原因是 -1 是您没有设置应用程序所需的设备功能以包括 GPS 或磁力计。设备可以决定不计算任何一个以节省电力。值得考虑的是您是否真的需要将此作为严格要求。