Implementing tabbar programatically.

Question

Hi, I am new to iphone development. Following is the code,- (void)activateTab:(int)index {

switch (index) {
    case 1:
        if (tab1ViewController == nil) {
            self.tab1ViewController =[[[CategoriesViewController alloc] 
                                       initWithNibName:@"CategoriesViewController" bundle:[NSBundle mainBundle]]
                                      autorelease];
        }
        [self.view insertSubview:tab1ViewController.view belowSubview:tabbar];
        if (currentViewController != nil)
            [currentViewController.view removeFromSuperview];
        currentViewController = tab1ViewController; 



        break;


    case 2:
        if (tab2ViewController == nil) {
            self.tab2ViewController =[[[CategoriesListViewController alloc]
                                       initWithNibName:@"CategoriesListViewController" bundle:[NSBundle mainBundle]]
                                      autorelease];

        }
        [self.view insertSubview:tab2ViewController.view belowSubview:tabbar];

        //[self.navigationController pushViewController:tab2ViewController animated:NO];

        if (currentViewController != nil)
            [currentViewController.view removeFromSuperview];


        currentViewController = tab2ViewController;     
        break;

    default:
        break;
}

}

Everything is fine with tab1ViewController and tab2ViewController. When i used to insert tab2ViewController to main view the viewDidLoad event is not being called. Can anyone help me out. Thanks in advance.