Is this a bug with MKMapKitDelegate mapView:didUpd

问题:

I've created a test application with only one view containing an MKMapView and a controller which acts as the MapView's delegate.

When I do a fresh build (removed from the device completely before re-installing) and log the callbacks, I can see that mapView:didUpdateUserLocation is called twice before the user has indicated whether they wish to show their current location or not.

The MKUserLocation objects passed to the callback are invalid:

2012-03-13 08:20:17.518 MapTest[3325:707] Did update user location: 0.000000,0.000000
2012-03-13 08:20:17.581 MapTest[3325:707] Did update user location: 0.000000,0.000000

Is this the expected behaviour for MKMapKit or a bug?

Update

I'm running this on my iPhone 4, not a simulator. Here's the controller code:

#import "ViewController.h"

@implementation ViewController

@synthesize mapView;

- (void)viewDidLoad
{
    [super viewDidLoad];

    self.mapView.showsUserLocation = YES;
    self.mapView.delegate = self;
}

- (void)viewDidUnload
{
    [super viewDidUnload];
    // Release any retained subviews of the main view.
}

-(IBAction)trackButtonTapped:(id)sender
{
    self.mapView.showsUserLocation = !self.mapView.showsUserLocation;
}

#pragma mark - MKMapKitDelegate

-(void)mapView:(MKMapView *)mapView didUpdateUserLocation:(MKUserLocation *)userLocation
{
    NSLog(@"Did update user location: %f,%f", userLocation.coordinate.latitude, userLocation.coordinate.longitude);
}

-(void)mapViewWillStartLoadingMap:(MKMapView *)mapView
{
    NSLog(@"Will start loading map");
}

-(void)mapViewDidFinishLoadingMap:(MKMapView *)mapView
{
    NSLog(@"Did finish loading map");    
}

-(void)mapViewWillStartLocatingUser:(MKMapView *)mapView
{
    NSLog(@"Will start locating user");
}

-(void)mapViewDidStopLocatingUser:(MKMapView *)mapView
{
    NSLog(@"Did stop locating user");
}

-(void)mapViewDidFailLoadingMap:(MKMapView *)mapView withError:(NSError *)error
{
    NSLog(@"Did fail loading map");
}

-(void)mapView:(MKMapView *)mapView didFailToLocateUserWithError:(NSError *)error
{
    if (error.code == kCLErrorDenied){
        NSLog(@"User refused location services");
    } else {
        NSLog(@"Did fail to locate user with error: %@", error.description);    
    }    
}

@end

回答1:

My opinion is that it's a bug.

How can the map view say user location has been updated when the user hasn't even granted permission?

The workaround I use is to check if userLocation.location is nil:

- (void)mapView:(MKMapView *)mapView didUpdateUserLocation:(MKUserLocation *)userLocation
{
    if (userLocation.location == nil)
        return;

    //do something with userLocation...
}

回答2:

instead checking for nil userlocation (where 0,0 coordinates can actually be valid) you should use:

if([CLLocationManager authorizationStatus] == kCLAuthorizationStatusAuthorized) {
  // do something with the coords
} else {
  // the coords are invalid
}

回答3:

With "self.mapView.showsUserLocation = YES;" in viewDidLoad it will start trying to get the user's location straight away. If you take that out it'll wait until the user has pressed a button.

回答4:

Maybe this helps someone. For me the "problem" was that I had set show user's location trough interface builder too. Removing it here and setting it through code made the delegate methods get work as suspected.