Weird "Property 'coordinate' requires method '-coordinate'" error

I've gotten to a point where I'm starting to think this is may actually be a bug in Xcode, but to be sure, I'm asking it here. I was working on my app that uses MapKit and CoreLocation, but at some point I started getting the warning "Property 'coordinate' requires method '-coordinate'". At first I thought I was doing something wrong, as I did use the property coordinate for an MKPointAnnotation, but after I commented that out, the warning remained.

In 开发者_Go百科fact, after I've commented out pretty much everything, I still get the warning. It tells me the file name and line number (the line with @end), but if I search for coordinate in that file, there aren't any results. The .h doesn't declare the property either, so I'm really lost as to where this error is coming from... I can provide you with code, of course, but I've commented so much stuff out that it doesn't really make any sense to post it here. Just a few memory management methods without any actual content other than sending a message to super...

Xcode is correct in telling you that you're required to implement -coordinate. This is a non-optional method of the MKAnnotation protocol.

http://developer.apple.com/library/ios/#documentation/MapKit/Reference/MKAnnotation_Protocol/Reference/Reference.html

coordinate The center point (specified as a map coordinate) of the annotation. (required) (read-only)

@property (nonatomic, readonly) CLLocationCoordinate2D coordinate

I believe the reason you can't synthesize coordinate is not because you didn't declare the property, but because you haven't told the compiler what storage to use.

Adding

CLLocationCoordinate2D coordinate;

to the fields (variables) section of your class interface will give the compiler the storage it is looking for.

Or you can point the compiler to other storage using this syntax:

@synthesize coordinate=myCoordinateVariable;

But none of that really matters, because you don't have to use synthesize.

Just implement the method yourself! The required part is readOnly so you only need to implement the getter.

-(CLLocationCoordinate2D)coordinate {
    return myCoordinate;
}

@property and @synthesize are primarily shortcuts. @synthesize just says to the compiler - "Implement these accessors if I haven't". But normally you declare a property like this, right?

@implementation MyClass : NSObject {
    NSString *someString;
}

@property (nonatomic, retain) NSString *someString;

and then you synthesize it. @synthesize creates the appropriate implementations for the declarations implied by @property:

-(NSString *)someString;
-(void)setSomeString:(NSString *);

and uses the storage you provided when you declared the instance variable, NSString *someString.

Incidentally, in Xcode 4 @synthesize automatically creates storage for you if it doesn't already exist.

I've had the same problem for over a year on one of my apps. Nobody has ever been able to offer an explanation. I just got to the point of adding a mapview to my latest app and had only gotten as far as adding the MapKit Framework to the project, declaring support for the MKMapViewDelegate and MKAnnotation protocols then I did the #imports for MapKit/MapKit.h and MapKit/MKAnnotation.h. Build the app and Bang! there's the warning.

So, I commented out the MKAnnotation protocol declaration and like magic the warning went away. The only conclusion I can come to is that this is an Xcode issue.

Very strange this problem. I just added the following line as Ball suggested and my warning disappeared.

@synthesize coordinate=myCoordinateVariable;

Thanks Ball for the info.