Why is App window only opening once and then not opening again?

Question

I am creating a app from a tutorial in a book, but I noticed a problem, when the preference window i created is opened and then closed it won't open again, how can i fix this?

Thanks.

EDIT: I saw another post about this but was still un-answered, so i was wondering if you could answer this for me.

EDIT: I am talking about a panel (used a preference pane), it is being opened via a Menu item, and is closed with the cross in the corner of the window. The code I used to create it was from the Book, Cocoa Programming For Mac OS X, the Panel which is being used as a preference pane is in a separate nib file.

EDIT: Here's the code, it's complicated as the tutorial made you create 4 files.

1) Preferences_Delegate.h

#import <Cocoa/Cocoa.h>
@class PreferenceController;

@interface Prefernces_Delegate : NSObject {
    PreferenceController *preferenceController;
}
- (IBAction)showPreferencePanel:(id)sender;

@end

2) Preferences_Delegate.m

#import "Prefernces_Delegate.h"
#import "PreferenceController.h"

@implementation Prefernces_Delegate

- (IBAction)showPreferencePanel:(id)sender
{
    // Is preferenceController nil?
    if (!preferenceController) {
     preferenceController = [[PreferenceController alloc] init];
    }
    NSLog(@"showing %@", preferenceController);
    [preferenceController showWindow:self];
}

@end

3) PreferencesController.h (Not Important)

#import <Cocoa/Cocoa.h>
@interface PreferenceController : NSWindowController {
    IBOutlet NSButton *checkbox;
}
- (IBAction)changeNewEmptyDoc:(id)sender;
@end

4) PreferencesController.m

#import "PreferenceController.h"


@implementation PreferenceController

- (id)init
{
    if (![super initWithWindowNibName:@"Preferences"])
     return nil;
    return self;
}
- (void)windowDidLoad
{
    NSLog(@"Nib file is loaded");
}
- (IBAction)changeNewEmptyDoc: (id)sender
{
    int state = [checkbox state];
     NSLog(@"Checkbox changed %d", state);
}




@end

Answer 1

In Interface Builder, make sure Release on close is turned off in the Window's attributes. Also double check that the connections to and from the window from your window controller are hooked up okay.

Answer 2

Make sure the window variable in the windowController is connected to the panel.