Mapkit mapview is not showing on first try - ios

Question

I have a tab on the RootViewController.m. The tab has 2 buttons. The first button upon click will go to CorpViewcontroller which has the mapView on it. When I click on the first button on the first try, the map is blank with google label on the bottom. I have to click back then click on the button again then the map show up. Is it possible to always show the map on the first button click?
My rootViewController.m to go to the second screen:
[self.navigationController pushViewController:self.corpController animated:YES];
The second screen called corpViewController has the following code:
- (void)viewDidLoad
{
[super viewDidLoad];
self.title = #"Set Remote Location";
self.jsonData = [[NSMutableData alloc] init];
mapView.showsUserLocation = YES;
//Setup the double tap gesture for getting the remote location..
UITapGestureRecognizer *tgr = [[UITapGestureRecognizer alloc]
initWithTarget:self action:#selector(handleGesture:)];
tgr.numberOfTapsRequired = 2;
tgr.numberOfTouchesRequired = 1;
[mapView addGestureRecognizer:tgr];
mapView.delegate = self;
NSLog(#"viewDidLoad done");
}
- (void)viewWillAppear:(BOOL)animated {
NSLog(#"viewWillAppear");
appDelegate = (NBSAppDelegate *)[[UIApplication sharedApplication] delegate];
double curLat = [appDelegate.curLat doubleValue];
MKUserLocation *userLocation = mapView.userLocation;
double miles = 10.0;
double scalingFactor = ABS( (cos(2 * M_PI * curLat / 360.0) ));
MKCoordinateSpan span;
span.latitudeDelta = miles/69.0;
span.longitudeDelta = miles/(scalingFactor * 69.0);
MKCoordinateRegion region2;
region2.span = span;
region2.center = userLocation.coordinate;
[mapView setRegion:region2 animated:YES];
NSLog(#"viewWillAppear done..");
}
Please Advise.
Thank you

Answer 1

Are you initializing the MapView in the viewDidLoad method in your view controller?
If so, try moving it to the viewDidAppear method. That worked for me.

Answer 2

In viewDidLoad you are setting showsUserLocation to YES and in viewWillAppear, you are zooming into the mapView.userLocation coordinate.
The userLocation property isn't usually ready with a valid coordinate immediately after setting showsUserLocation to YES.
The first time you show the view controller, it's still invalid and you are zooming into the coordinate 0,0.
By the time you show the view controller a second time, the user location has been obtained and the coordinate is valid.
Instead of zooming into the user location in viewWillAppear, do it in the delegate method mapView:didUpdateUserLocation: which the map view calls when it gets a user location update.
In addition, you also probably want to move the mapView.showsUserLocation = YES; to viewWillAppear and in viewWillDisappear, set it to NO. This way, the map view will zoom in to the user location every time the view controller is shown instead of just the first time.
An unrelated point is that to zoom in to a specific distance, it's much easier to use the MKCoordinateRegionMakeWithDistance function instead of trying to convert miles to degrees yourself.
Here's an example of the changes suggested in corpViewController:
- (void)viewWillAppear:(BOOL)animated
{
//move this from viewDidLoad to here...
mapView.showsUserLocation = YES;
}
-(void)viewWillDisappear:(BOOL)animated
{
mapView.showsUserLocation = NO;
}
-(void)mapView:(MKMapView *)mv didUpdateUserLocation:(MKUserLocation *)userLocation
//Changed the **internal** parameter name from mapView to mv
//to avoid a compiler warning about it hiding instance var with same name.
//It's better to use the passed parameter variable anyway.
{
NSLog(#"didUpdateUserLocation");
double miles = 10.0;
//Instead of manually calculating span from miles to degrees,
//use MKCoordinateRegionMakeWithDistance function...
//Just need to convert miles to meters.
CLLocationDistance meters = miles * 1609.344;
MKCoordinateRegion region2 = MKCoordinateRegionMakeWithDistance
(userLocation.coordinate, meters, meters);
[mv setRegion:region2 animated:YES];
}