MapKit, Dropping pin on one location with button - ios

Question

Trying to learn how to have a pin drop at a users location when they push a button on screen. Do I need to use Mkannotation, also I want this pin to disappear when they drop a new pin in the future. This is the code I have in controller.h. Also the longitude and latitude are just for example.
thanks
#implementation ViewController
- (void)viewWillAppear:(BOOL)animated {
CLLocationCoordinate2D zoomLocation;
zoomLocation.latitude = 39.281516;
zoomLocation.longitude = -76.580806;
MKCoordinateRegion viewRegion = MKCoordinateRegionMakeWithDistance(zoomLocation,
0.1*METERS_PER_MILE, 0.1*METERS_PER_MILE);
[_mapView setRegion:viewRegion animated:YES];
}

Answer 1

While I think this is discussed in some detail in the Adding Annotations to a Map section of the Location Awareness Programming Guide, I have a few observations:
You ask "do I need to use MKAnnotation?" Yes and no.
Yes, all annotations should conform to the MKAnnotation protocol. As that guide describes, if you can create your own annotation subclass, you'd want it explicitly declare it to conform to the MKAnnotation protocol.
But, no, you don't have to always create your own annotation class that conforms to the MKAnnotation protocol. You can also use a predefined annotation class, MKPointAnnotation (which, itself, already conforms to the MKAnnotation protocol), such as:
MKPointAnnotation *annotation = [[MKPointAnnotation alloc] init];
annotation.coordinate = CLLocationCoordinate2DMake(39.281516, -76.580806);
annotation.title = #"Lens Crafters";
annotation.subtitle = #"2400 Boston St.";
[self.mapView addAnnotation:annotation];
If you want the old annotation to disappear when you drop a new one on your map, you just (a) keep a reference to the old annotation; (b) when adding a new annotation, remove the old one (if you have an old one); and then (c) add your new annotation.
Thus you might have defined some class property for your annotation:
#property (weak, nonatomic) id<MKAnnotation> annotation;
(Two side observations: First, whether you use weak or strong is up to you and your app design. By saying weak, I'm saying that when the annotation is removed from the map, I'm happy to have the annotation released. Maybe you want it retained until you explicitly nil this property, in which case you'd make this property strong. That's entirely up to you and the goals of your app. Second, I use the type id<MKAnnotation> (i.e. "an object that conforms to MKAnnotation") which makes this more flexible. If you later replace MKPointAnnotation with your own custom annotation class, this property will still work. But if you want to explicitly define this annotation property to be a MKPointAnnotation to match your annotation adding routine, that's fine, too.)
Anyway, now that you have this property, you can now write a method to add an annotation to your map (which removes the old one):
- (void)addAnnotationAtCoordinate:(CLLocationCoordinate2D)coordinate
title:(NSString *)title
subtitle:(NSString *)subtitle
{
if (self.annotation)
[self.mapView removeAnnotation:self.annotation];
MKPointAnnotation *annotation = [[MKPointAnnotation alloc] init];
annotation.coordinate = coordinate;
annotation.title = title;
annotation.subtitle = subtitle;
[self.mapView addAnnotation:annotation];
self.annotation = annotation;
}