Add project files.

DIDemoLib/DIDemoLib.csproj

@@ -0,0 +1,9 @@
+<Project Sdk="Microsoft.NET.Sdk">
+
+  <PropertyGroup>
+    <TargetFramework>net7.0</TargetFramework>
+    <ImplicitUsings>enable</ImplicitUsings>
+    <Nullable>enable</Nullable>
+  </PropertyGroup>
+
+</Project>

DIDemoLib/IMessages.cs

@@ -0,0 +1,8 @@
+namespace DIDemoLib
+{
+    public interface IMessages
+    {
+        string SayGoodBye();
+        string SayHello();
+    }
+}

DIDemoLib/Messages.cs

@@ -0,0 +1,14 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+using System.Threading.Tasks;
+
+namespace DIDemoLib
+{
+    public class Messages : IMessages
+    {
+        public string SayHello() => "Hello Viewer";
+        public string SayGoodBye() => "Goodbye, farewell and good day!";
+    }
+}