RelayCommand

MvvmCommunityApp/App.xaml.cs

@@ -3,6 +3,7 @@ using Microsoft.Extensions.DependencyInjection;
 using MvvmCommunityApp.interfaces;
 using MvvmCommunityApp.services;
 using MvvmCommunityApp.viewmodels;
+using System;
 using System.Windows;
 
 namespace MvvmCommunityApp
@@ -12,17 +13,35 @@ namespace MvvmCommunityApp
     /// </summary>
     public partial class App : Application
     {
-        protected override void OnStartup(StartupEventArgs e)
+        public new static App Current => (App)Application.Current;
+
+        public App()
         {
-            base.OnStartup(e);
+            // !!! Add constructor initialization HERE !!!!
+            // configure mvvm ioc
+            ConfigureServices();
+        }
 
+        private void ConfigureServices() =>
             // setup mvvm ioc
             Ioc.Default.ConfigureServices(
                 new ServiceCollection()
                     .AddTransient<IocPageViewModel>()
                     .AddSingleton<IDemoService, DemoService>()
+                    .AddSingleton<MainWindowViewModel>()
                     .BuildServiceProvider());
 
+        protected override void OnStartup(StartupEventArgs e)
+        {
+            base.OnStartup(e);
+
+            // setup mvvm ioc
+            //Ioc.Default.ConfigureServices(
+            //    new ServiceCollection()
+            //        .AddTransient<IocPageViewModel>()
+            //        .AddSingleton<IDemoService, DemoService>()
+            //        .BuildServiceProvider());
+
             // load the main / entry page
             MainWindow wnd = new MainWindow();
 

MvvmCommunityApp/MainWindow.xaml

@@ -8,7 +8,9 @@
         Title="MainWindow" Height="450" Width="800">
     <Grid>
         <StackPanel>
-            <TextBlock Text="{Binding MyName}" />
+            <TextBlock Text="{Binding Title}" />
+            <Button Content="Add"
+                    Command="{Binding AddCommand}" />
         </StackPanel>
     </Grid>
 </Window>

MvvmCommunityApp/MainWindow.xaml.cs

@@ -19,7 +19,7 @@ namespace MvvmCommunityApp
 
             InitializeComponent();
 
-            DataContext = Ioc.Default.GetRequiredService<IocPageViewModel>();
+            DataContext = Ioc.Default.GetRequiredService<MainWindowViewModel>();
         }
     }
 }

MvvmCommunityApp/viewmodels/MainWindowViewModel.cs

@@ -0,0 +1,28 @@
+using CommunityToolkit.Mvvm.ComponentModel;
+using CommunityToolkit.Mvvm.Input;
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+using System.Threading.Tasks;
+
+namespace MvvmCommunityApp.viewmodels
+{
+    public class MainWindowViewModel : ObservableObject
+    {
+        public string Title { get; set; }
+        public RelayCommand AddCommand { get; }
+
+        public MainWindowViewModel() 
+        {
+            Title = "MyIocName";
+            //
+            AddCommand = new RelayCommand(DoAdd);
+        }
+
+        private void DoAdd()
+        {
+            Console.WriteLine("Do Add");
+        }
+    }
+}