How to save a user's credentials in the 'XAF_Security_E4908/XPO/Xamarin.Forms' example

save user's credentials when the user logs in for the first time

We don't offer any special mechanism to save/restore data in a Xamarin application, so you need to use common Xamarin techniques for this. You can refer to Xamarin support resources to find the most suitable way. I suggest starting with the following article: Xamarin.Essentials: Secure Storage - Xamarin | Microsoft Docs.

when the user logs in the next time, reuse the saved credentials to log the user in (and skip the logon window).

To accomplish this task, modify the App() method in the App.xaml.cs file so that it automatically logs in a user if there are stored credentials. You can see the code that logs in a user here: LoginViewModel.cs. Your modified code can look as follows:

C#
using DevExpress.Persistent.Base;
using System;
using Xamarin.Forms;
using XamarinFormsDemo.Views;

namespace XamarinFormsDemo {
    public partial class App : Application {
        public App() {
        //...
          var storedCredentials = GetStoredCredentials();
          if(storedCredentials == default) {
            SetStartupPage(new LoginPage());
          } else {
             XpoHelper.InitXpo(WebApiDataStoreClient.GetConnectionString("https://10.0.2.2:5001/xpo/"), storedCredentials.login, storedCredentials.pasword);
           SetStartupPage(new MainPage());
    }
}




private void SetStartupPage(ContentPage contentPage) {
    if(Device.RuntimePlatform == Device.iOS)
        MainPage = contentPage;
    else
        MainPage = new NavigationPage(contentPage);
}



static (string login, string pasword) GetStoredCredentials() => throw new NotImplementedException("TODO");