Working with ViewControllers in Objective-C
#import "AppDelegate.h"
#import "LoginViewController.h"

@implementation AppDelegate

@synthesize window = _window;
@synthesize viewController = _viewController;

- (void)applicationDidFinishLaunching:(NSNotification *)aNotification
{
self.viewController = [[LoginViewController alloc]    initWithNibName:@"LoginWindowController" bundle:nil];
[self.window setContentView:[self.viewController view]];
}

- (BOOL)applicationShouldHandleReopen:(NSApplication *)theApplication hasVisibleWindows:(BOOL)flag {

[self.window makeKeyAndOrderFront:self];

return YES;
}

@end

#import "LoginViewController.h"

@interface LoginViewController ()

@end

@implementation LoginViewController
@synthesize usernameField;
@synthesize passwordField;

- (id)initWithNibName:(NSString *)nibNameOrNil bundle:(NSBundle *)nibBundleOrNil
{
self = [super initWithNibName:nibNameOrNil bundle:nibBundleOrNil];
if (self) {
    // Initialization code here.
}

return self;
}
- (IBAction)loginPressed:(NSButton *)sender
{
NSLog(@"Username = %@", [self.usernameField stringValue]);
NSLog(@"Password = %@", [self.passwordField stringValue]);
}

@end