How to delete the last annotation on a mapView

问题:

I have added a button on my .xib file with which I want to delete the last annotation that has been added.

So on the Touch-Down action I have implemented this:

-(IBAction)DeleteAnnotation:(id)sender {
   [mapview removeAnnotation:[mapview.annotations lastObject]];
}

and I have even tried it this way:

-(IBAction)DeleteAnnotation:(id)sender {
   [self.mapview removeAnnotation:self.mapview.annotations.lastObject]];
}

where mapview is my MKMapView Outlet.

The problem I encounter with both ways is that I have to press this specific button quite a few times before an annotation is removed.

Furthermore, the annotations remove themselves in a quite random way.

Is there something I am doing wrong or is it a software and simulator matter?

回答1:

The annotations property of MKMapView is not guaranteed to return the annotations in the same order that you added them.

Making the assumption that the annotations array property will return the annotations in the same order that you added them is most likely the reason for the "strange" behavior you see. Please see these related answers for some more details:

• MKMapView annotations changing/losing order?
• How to reorder MKMapView annotations array

To get the behavior you want (which I assume is simply "remove the last annotation that was added explicitly by my code"), here are three possible approaches (there may be others):

1. Simplest approach is to keep a reference in a strong property to the last annotation you add (update the reference when you call addAnnotation). When you want to remove the "last annotation added", pass that saved reference to removeAnnotation. For example:

   //in the interface...
   @property (nonatomic, strong) id<MKAnnotation> lastAnnotationAdded;
   
   //in the implementation...
   
   //when you add an annotation:
   [mapview addAnnotation:someAnnotation];
   self.lastAnnotationAdded = someAnnotation;  //save the reference
   
   //when you want to remove the "last annotation added":
   if (self.lastAnnotationAdded != nil)
   {
       [mapview removeAnnotation:self.lastAnnotationAdded];
       self.lastAnnotationAdded = nil;
   }
   

2. Another option is to loop through the map view's annotations array and search for the "last" annotation (or whatever attribute you're interested in). Once you have a reference to the "last" one (which may not necessarily be the last object in the array), you can call removeAnnotation on it. This approach assumes you have some property in the annotation objects themselves that let you identify an annotation as the "last" one. This may not always be possible.

3. Another option is to keep your own array of annotations and add annotation objects to this array whenever you call addAnnotation. This is similar to keeping the single reference to just the "last annotation added" except you keep track of the entire list in an order you can rely on. To remove the "last" one, you would get lastObject from your array instead of the map view's (assuming you keep the array in that order). You have to make sure to keep your array in sync as you add/remove annotations from the map.