Storyboard开发时，介绍界面怎么弹出

如题，在用storyboard开发时，如果用户第一次打开则显示欢迎界面。我是在mainController里面用modal的方式显示的，但是之前会看到一下mainController的界面，我想直接进入欢迎界面，并且完成之后能够跳转回来。有没比较好的方案啊

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如下所示：

- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions {
    window = [[UIWindow alloc] initWithFrame:[[UIScreen mainScreen] bounds]];

    UIStoryboard* mainStoryboard = [UIStoryboard storyboardWithName:@"Main" bundle:nil];

    if(![[NSUserDefaults standardUserDefaults] objectForKey:@"first_launch"]){
        WelcomeViewController *welcome = [mainStoryboard instantiateViewControllerWithIdentifier:@"welcome"];
        window.rootViewController = welcome;
        [[NSUserDefaults standardUserDefaults] setBool:YES forKey:@"first_launch"];
    }else{
        if([[NSUserDefaults standardUserDefaults] objectForKey:@"isBind"]){
            QRViewController *qreader = [mainStoryboard instantiateViewControllerWithIdentifier:@"qreader"];
            window.rootViewController = qreader;
        }else{
            BindViewController *bind = [mainStoryboard instantiateViewControllerWithIdentifier:@"bind"];

            window.rootViewController = bind;
        }
    }
        [window makeKeyAndVisible];

    return YES;
}

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展示的时候把动画去掉应该就看不见了