添加项目文件。

ViewModels/MainViewModel.cs

@@ -0,0 +1,24 @@
+using CommunityToolkit.Mvvm.ComponentModel;
+using CommunityToolkit.Mvvm.Messaging;
+using PMSWPF.Message;
+
+namespace PMSWPF.ViewModels
+{
+    partial class MainViewModel : ObservableRecipient, IRecipient<MyMessage>
+    {
+        public MainViewModel()
+        {
+            IsActive = true;
+        }
+
+        string text = "Hello Count:";
+
+        [ObservableProperty]
+        string message;
+
+        public void Receive(MyMessage message)
+        {
+            Message = text + message.Count;
+        }
+    }
+}