Question

我有一个UIViewController，我想显示一个以当前位置为中心的地图。

AppDelegate＆lt; strong> didFinishLaunchingWithOptions 方法如下所示：

- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions {
    self.locationManager = [[CLLocationManager alloc] init];

    if ([CLLocationManager authorizationStatus] == kCLAuthorizationStatusNotDetermined) {
        [self.locationManager requestAlwaysAuthorization];
    }
    [self.locationManager startUpdatingLocation];

    return YES;
}

我的 UIViewController.m 类看起来像这样：

@interface GMapViewController ()<CLLocationManagerDelegate>

@property (weak, nonatomic) IBOutlet MKMapView *mapView;
@property (strong, nonatomic) CLLocation *currentLocation;

@end

@implementation GMapViewController

#pragma mark - Lifecycle methods

- (void)viewDidLoad {
    [super viewDidLoad];

    self.currentLocation = [CLLocation new];

    [[[AppDelegate appDelegate] locationManager] setDelegate:self];

    MKCoordinateRegion visibleRegion;
    visibleRegion.center = self.currentLocation.coordinate;
    visibleRegion.span = MKCoordinateSpanMake(200, 200);

    [self.mapView setRegion:visibleRegion animated:YES];
}

#pragma mark - CLLocationManagerDelegate's methods

- (void)locationManager:(CLLocationManager *)manager didUpdateLocations:(NSArray<CLLocation *> *)locations {
    self.currentLocation = [locations lastObject];
}

事实是CLLocationManager的 didUpdateLocations 委托方法被调用太晚，因为当 viewDidLoad 时 currentLocation 属性没有值被称为。

如何在调用 viewDidLoad 之前获取当前坐标？

Answer 1

位置更新后，您需要刷新地图视图;这需要一些时间。

您还有潜在的竞争条件，因为您在AppDelegate中调用startUpdatingLocation，但视图控制器在viewDidLoad之前未设置为代理。在更新位置之前几乎肯定会设置代表，但您无法保证这一点。

我建议您将所有内容移动到视图控制器中，如果您只想更新一次地图，请使用requestLocation：

@interface GMapViewController ()<CLLocationManagerDelegate>

@property (weak, nonatomic) IBOutlet MKMapView *mapView;
@property (strong, nonatomic) CLLocation *currentLocation;
@property (strong, nonatomic) CLLocationManager *locationManager;

@end

@implementation GMapViewController

#pragma mark - Lifecycle methods

- (void)viewDidLoad {
    [super viewDidLoad];

    self.locationManager = [[CLLocationManager alloc] init];
    self.currentLocation = nil;

        if ([CLLocationManager authorizationStatus] == kCLAuthorizationStatusNotDetermined) {
            [self.locationManager requestAlwaysAuthorization];
        } else {
            [self.locationManager requestLocation];
}

-(void) setMapTo:(CLLocation *)location {
      MKCoordinateRegion visibleRegion;
      visibleRegion.center =location.coordinate;
      visibleRegion.span = MKCoordinateSpanMake(200, 200);

     [self.mapView setRegion:visibleRegion animated:YES];
}

#pragma mark - CLLocationManagerDelegate's methods

- (void)locationManager:(CLLocationManager *)manager didUpdateLocations:(NSArray<CLLocation *> *)locations {
    CLLocation *currentLocation = [locations lastObject];
    dispatch_async(dispatch_get_main_queue(), ^{
          [self setMapTo:currentLocation];
    });
}
- (void)locationManager:(CLLocationManager *)manager didChangeAuthorizationStatus:(CLAuthorizationStatus)status {
    if (status != kCLAuthorizationStatusRestricted && status != kCLAuthorizationStatusDenied) {
        [manager requestLocation];
    }
}

如果您只是希望地图能够持续跟踪用户的位置，那么您只需将地图视图的userTrackingMode属性设置为MKUserTrackingModeFollow

如何获取CLLocationManager的当前坐标

1 个答案: