NSTextField don't update after click

Question

I create a easy application. I create one class for show the coordinate from mouse.

my .m file

#import <Cocoa/Cocoa.h>

@interface MousePossition : NSView{
    IBOutlet NSTextField *coordinateLabel;
    NSPoint mouseLocation;
}

@end

and my .h

#import "MousePossition.h"

@implementation MousePossition

- (void)mouseDown:(NSEvent *)theEvent{
    // Enregistrement des coordonées dans mouseLocation
    mouseLocation = [theEvent locationInWindow];

    [self updateCoordonateLabel];

    // Vérification de l'exécution
    NSLog(@"Clicked %f %f",mouseLocation.x,mouseLocation.y);
}

-(void)updateCoordonateLabel
{
    NSString *a = [NSString stringWithFormat:@"X : %f\n X : %f", mouseLocation.x, mouseLocation.y];

    // MàJ du Label avec les coordonées
    [coordinateLabel setStringValue:a];
    NSLog(@"%@", a);
}

@end

But the label don't update after click on my mouse! Any idea what is the problem? If I create a button and convert -(void)updateCoordonateLabel to -(IBAction)updateCoordonateLabel:(id)senderthe label show always 0.0000 on x and y