問題：今天在項目中遇到這樣一個需求，tabBar上有首頁棚瘟，商家现斋，購物車，個人中心四個模塊偎蘸，當(dāng)點擊商家和購物車時要判斷用戶是否已經(jīng)登錄庄蹋，如果沒有就要跳轉(zhuǎn)到登錄界面，登錄成功后回到指定的控制器迷雪，就拿購物車來說限书，登錄成功后自動跳到購物車界面去

思路：在AppDelegate里面設(shè)置tabBarController的代理為self，在- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions方法中添加監(jiān)聽事件章咧，登錄成功發(fā)送通知我碟，通知信息里面?zhèn)鬟ftabBar的selectIndex值涕烧，至于如何傳遞這個值有很多方法。然后實現(xiàn)- (BOOL)tabBarController:(UITabBarController *)tabBarController shouldSelectViewController:(UIViewController *)viewController方法，跳轉(zhuǎn)到登錄控制器押赊，登錄完成自動跳回

以下是AppDelegate核心代碼：

- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions {
    [[NSNotificationCenter defaultCenter]addObserver:self selector:@selector(logSelect:) name:LoginSuccessNotification object:nil];//接收成功的通知
    }

- (BOOL)tabBarController:(UITabBarController *)tabBarController shouldSelectViewController:(UIViewController *)viewController
{
    //這里我判斷的是當(dāng)前點擊的tabBarItem的標(biāo)題
    if ([viewController.tabBarItem.title isEqualToString:@"購物車"])
    {
        //我的登錄狀態(tài)存放在本地
        if ([[[NSUserDefaults standardUserDefaults] objectForKey:LoginStatu] isEqualToString:successLogin]) {
            return YES;
        }
        else//未登錄
        {
            //跳到登錄頁面亥贸，這里我是用單利來存儲tabbar的selectIndex的辞州，個人習(xí)慣
            LoginViewController *login = [[LoginViewController alloc] init];
            [MKJRequestHelper shareRequestHelper].selectIndex = @"2";
            login.hidesBottomBarWhenPushed = YES;
            [((UINavigationController *)tabBarController.selectedViewController) pushViewController:login animated:YES];
            return NO;
        }
    }

    //如果是商家
    else if([viewController.tabBarItem.title isEqualToString:@"商家"])
     {
            if ([[[NSUserDefaults standardUserDefaults] objectForKey:LoginStatu] isEqualToString:successLogin])
         {
            return YES;
         }
        else
        {
            //跳到登錄頁面
            LoginViewController *login = [[LoginViewController alloc] init];
             [MKJRequestHelper shareRequestHelper].selectIndex = @"1";
            login.hidesBottomBarWhenPushed = YES;
            [((UINavigationController *)tabBarController.selectedViewController) pushViewController:login animated:YES];
            return NO;
        }
    
    }
    return YES;
}


//登錄成功接受到的方法逃贝，讓tabBarConroller直接跳轉(zhuǎn)到你想跳的界面中去
- (void)logSelect:(NSNotification *)text{
    
   _tabBarVC.selectedIndex = [text.userInfo[@"index"]integerValue];
    
}

登錄控制器的代碼就只有發(fā)送通知就可以了，