WPF Displays the login success first, the main window appears after validation succeeds

To set how to display the login window:
In the App.xaml, this sentence
Delete startupuri= "MainWindow.xaml" to Startupuri= "Login/loginwindow.xaml"//Login/loginwindow.xaml is the login window;
Plus shutdownmode= "Onlastwindowclose"

The code is as follows:

     Public Partial classLoginwindow:window { PublicLoginwindow () {InitializeComponent (); }        Private voidbtnClose_Click (Objectsender, RoutedEventArgs e)        {System.Windows.Application.Current.Shutdown (); }        Private voidBtnlogin_click (Objectsender, RoutedEventArgs e) {            if(user_name. Text! = loginconfig.getsettingstring ("UserName") ||password. Password! = loginconfig.getsettingstring ("Password") {MessageBox.Show ("The user name or password is wrong! "); }            Else            {                (NewMainWindow ()). Show ();//display the main window;Close (); }        }    }

WPF Displays login success first, show main window after successful validation