Using IBAction Buttons to Zoom MapView

Question

I have an issue. My current location is displayed and centered in a map view however the map region doesn't get zoomed in to. I tried taking Rob's advice by taking span and region out of the didUpdateToLocation method but I must not have implemented it right. I don't think it's recognizing my call to setRegion in viewDidLoad and my buttons aren't being recognized. Please check my code below and point out the mistake(s). My goal is to be able to zoom in and out of my location using the IBAction buttons.

.h

- (IBAction)zoomIn:(id)sender;

- (IBAction)zoomOut:(id)sender;

.m in viewDidLoad

double miles = 0.5;

MKCoordinateSpan span;
span.latitudeDelta = miles/69.0;
span.longitudeDelta = miles/69.0;

MKCoordinateRegion region;
region.span = span;

[self.mapView setRegion:region animated:YES];

[self.mapView setUserTrackingMode:MKUserTrackingModeFollow animated:YES];

_mapView.mapType = MKMapTypeSatellite;

.m in my didUpdateToLocation method.

[self.mapView setCenterCoordinate:newLocation.coordinate animated:YES];

.Zoom In:

- (IBAction)zoomIn:(id)sender 
{
    MKCoordinateSpan span;
    span.latitudeDelta = _mapView.region.span.latitudeDelta * 2;
    span.longitudeDelta = _mapView.region.span.latitudeDelta * 2;
    MKCoordinateRegion region;
    region.span = span;
    region.center = _mapView.region.center;

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

.Zoom Out :

- (IBAction)zoomOut:(id)sender
{
     MKCoordinateSpan span;
     span.latitudeDelta = _mapView.region.span.latitudeDelta / 2;
     span.longitudeDelta = _mapView.region.span.latitudeDelta / 2;
     MKCoordinateRegion region;
     region.span = span;
     region.center = _mapView.region.center;

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

Answer 1

You can get the current region, multiply or divide the span by two, as appropriate (dividing on zoom in, multiplying on zoom out), and then set the region:

- (IBAction)zoomIn:(id)sender {
    MKCoordinateRegion region = self.mapView.region;
    region.span.latitudeDelta /= 2.0;
    region.span.longitudeDelta /= 2.0;
    [self.mapView setRegion:region animated:YES];
}

- (IBAction)zoomOut:(id)sender {
    MKCoordinateRegion region = self.mapView.region;
    region.span.latitudeDelta  = MIN(region.span.latitudeDelta  * 2.0, 180.0);
    region.span.longitudeDelta = MIN(region.span.longitudeDelta * 2.0, 180.0);
    [self.mapView setRegion:region animated:YES];
}

---

If you want to have the map automatically zoom to your location, you can use:

self.mapView.userTrackingMode = MKUserTrackingModeFollow;

If you want to do this manually, you can do something like the following. First, define an class property for whether you've zoomed in already or not:

@property (nonatomic) BOOL alreadySetZoomScale;

then change your didUpdateLocations (or didUpdateToLocation) to check this and set the zoom scale once:

- (void)locationManager:(CLLocationManager *)manager didUpdateLocations:(NSArray *)locations
{
    CLLocation* newLocation = [locations lastObject]; // if less than zero, then valid lat and long not found

    if (newLocation.horizontalAccuracy < 0)
        return;

    if (!self.alreadySetZoomScale)
    {
        MKCoordinateRegion region = MKCoordinateRegionMakeWithDistance(newLocation.coordinate, 1609, 1609); // 1 mile = 1609.34 meters
        self.mapView.region = region;
        [self.mapView setRegion:region animated:YES];
        self.alreadySetZoomScale = YES;
    }
    else
    {
        [self.mapView setCenterCoordinate:newLocation.coordinate animated:YES];
    }
}

- (void)locationManager:(CLLocationManager *)manager didUpdateToLocation:(CLLocation *)newLocation fromLocation:(CLLocation *)oldLocation
{
    // if prior to iOS 6, use this old `MKMapViewDelegate` method, but call our
    // other routine.

    if (SYSTEM_VERSION_LESS_THAN(@"6.0"))
        [self locationManager:manager didUpdateLocations:@[newLocation]];
}

This basically says, "if I haven't zoomed in yet, set the region based upon the newLocation and a certain number of meters around that location, but if I have already done that, the just set the center coordinate based upon my current location, but don't change the zoom scale (in case I already zoomed in or out). This also does some conditional iOS version number logic (using the macros shown here), making sure if the end-user is running iOS prior to 6.0, that it will call our updated method.

By the way, if you're showing the user location on the map (e.g. self.mapView.showsUserLocation = YES;), you might want to have this didUpdateLocations also remove the overlay associated with the MKUserLocation before moving the map center, otherwise it can leave the old overlay sitting around:

[self.mapView removeOverlays:self.mapView.overlays];