Objective-c – Load annotations for visible region in MKMapView

iphone-sdk-3.0objective c

I have about 400 MKAnnotationView´s that loads simultaneously into the MKMapView.

I understand that this isn't any good, it is a little bit slow, and I want to do it the "correct" way.

I zoom my map by a center coordinate:

MKCoordinateSpan span;
span.latitudeDelta = 0.8;
span.longitudeDelta = 0.8;

MKCoordinateRegion region;
region.span = span;

region.center = self.selectedCounty.coordinate;

[mapView setRegion:region animated:TRUE];

I only want to load the annotations that could be visible in that region.

I have a custom MKAnnotation called simply "Annotation" with a CLLocationCoordinate2D- and title-property.

I simply want to load the annotation for the "visible area" on the MKMapView so not all the annotation loads at the same time. And when the "visible area" on the MKMapView changes, I of course want to load annotations for that area.

I know that MKMapView has a delegate method which runs when the region changes.

But how do I know what annotations I should load for that region?

Best Answer

MKMapRect visibleMapRect = mapView.visibleMapRect;
NSSet *visibleAnnotations = [mapView annotationsInMapRect:visibleMapRect];

Related Solutions

Ios – Removing MKMapView Annotations causes leaks

You're not releasing mymark in storeLocationInfo:title:subtitle:index:. It looks like the problem is a typing error. The line that reads

[MyMark release];

should be

[mymark release];

Note the case difference. The first line sends release to the class, not the instance.

Objective-c – Set MKMapView region to center on two annotations

For iOS7 forward the best way to do this is:

//from API docs: 
//- (void)showAnnotations:(NSArray *)annotations animated:(BOOL)animated NS_AVAILABLE(10_9, 7_0);
[self.mapView showAnnotations:self.mapView.annotations animated:YES];

For my personal project (prior to iOS7) I simply added a category on the MKMapView class to encapsulate the "visible area" functionality for a very common operation: setting it to be able to see all the currently-loaded annotations on the MKMapView instance (this includes as many pins as you might have placed, as well as the user's location). the result was this:

.h file

#import <MapKit/MapKit.h>

@interface MKMapView (Extensions)

-(void)ij_setVisibleRectToFitAllLoadedAnnotationsAnimated:(BOOL)animated;
-(void)ij_setVisibleRectToFitAnnotations:(NSArray *)annotations animated:(BOOL)animated;


@end

.m file

#import "MKMapView+Extensions.h"

@implementation MKMapView (Extensions)

/**
 *  Changes the currently visible portion of the map to a region that best fits all the currently loadded annotations on the map, and it optionally animates the change.
 *
 *  @param animated is the change should be perfomed with an animation.
 */
-(void)ij_setVisibleRectToFitAllLoadedAnnotationsAnimated:(BOOL)animated
{
    MKMapView * mapView = self;

    NSArray * annotations = mapView.annotations;

    [self ij_setVisibleRectToFitAnnotations:annotations animated:animated];

}


/**
 *  Changes the currently visible portion of the map to a region that best fits the provided annotations array, and it optionally animates the change.
    All elements from the array must conform to the <MKAnnotation> protocol in order to fetch the coordinates to compute the visible region of the map.
 *
 *  @param annotations an array of elements conforming to the <MKAnnotation> protocol, holding the locations for which the visible portion of the map will be set.
 *  @param animated    wether or not the change should be perfomed with an animation.
 */
-(void)ij_setVisibleRectToFitAnnotations:(NSArray *)annotations animated:(BOOL)animated
{
    MKMapView * mapView = self;

    MKMapRect r = MKMapRectNull;
    for (id<MKAnnotation> a in annotations) {
        ZAssert([a conformsToProtocol:@protocol(MKAnnotation)], @"ERROR: All elements of the array MUST conform to the MKAnnotation protocol. Element (%@) did not fulfill this requirement", a);
        MKMapPoint p = MKMapPointForCoordinate(a.coordinate);
        //MKMapRectUnion performs the union between 2 rects, returning a bigger rect containing both (or just one if the other is null). here we do it for rects without a size (points)
        r = MKMapRectUnion(r, MKMapRectMake(p.x, p.y, 0, 0));
    }

    [mapView setVisibleMapRect:r animated:animated];

}

@end

As you can see, I've added 2 methods so far: one for setting the visible region of the map to the one that fits all currently-loaded annotations on the MKMapView instance, and another method to set it to any array of objects. So to set the mapView's visible region the code would then be as simple as:

   //the mapView instance  
    [self.mapView ij_setVisibleRectToFitAllLoadedAnnotationsAnimated:animated];

I hope it helps =)

Best Answer

Related Solutions

Ios – Removing MKMapView Annotations causes leaks

Objective-c – Set MKMapView region to center on two annotations

Related Topic