Loging out issue in iphone sdk

I have created an tabbar based iphone app, for the login page i used the following method:

@protocol LoginViewControllerDelegate;
@interface TradeBarcodeViewController: UIViewController{
id<LoginViewControllerDelegate> delegate;
}
@protocol LoginViewControllerDelegate
-(void)loginViewControllerDidFinish:(TradeBarcodeViewController *)loginViewController;
@end

@implementation TradeBarcodeViewController

[self.delegate loginViewControllerDidFinish:self];
@end

It is working fine and I can loggin to the tabbar controled app. In one of the tabbar viewconroller there is a button for Logout. I used the following for that:

TradeBarcodeViewController *vc = [[TradeBarcodeViewController alloc]init];
    [self presentModalViewController:vc
                            animated:NO];
    [vc release];

Then 开发者_如何学Cit will again navigate to the login page, but if I try to login again it is not working. What went wrong here? Or which method should I use to logout from my app? Thanks.

---

if your login page is not in tabbar then when u click logout use this code

//here u need to clear the field from database which checks for username and password [tabBar.view removeFromSuperview];

[tabBar release];

tabBar = nil;

[self addLoginPage];

Then in addLoginPage function add this

LoginPageViewController *loginView = [[LoginPageViewController alloc] init];

navigation=[[UINavigationController alloc]initWithRootViewController:loginView];


[window addSubview:navigation.view];