修改

ClassLibrary2/Class1.cs

@@ -5,6 +5,7 @@ using System.Text;
 
 namespace ClassLibrary2
 {
+    //123
     public class Class1
     {
     }

ClassLibrary2/Class2.cs

@@ -0,0 +1,11 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+
+namespace ClassLibrary2
+{
+    class Class2
+    {
+    }
+}

ClassLibrary2/ClassLibrary2.csproj

@@ -1,10 +1,10 @@
-<?xml version="1.0" encoding="utf-8"?>
+<?xml version="1.0" encoding="utf-8"?>
 <Project ToolsVersion="15.0" xmlns="http://schemas.microsoft.com/developer/msbuild/2003">
   <Import Project="$(MSBuildExtensionsPath)\$(MSBuildToolsVersion)\Microsoft.Common.props" Condition="Exists('$(MSBuildExtensionsPath)\$(MSBuildToolsVersion)\Microsoft.Common.props')" />
   <PropertyGroup>
     <Configuration Condition=" '$(Configuration)' == '' ">Debug</Configuration>
     <Platform Condition=" '$(Platform)' == '' ">AnyCPU</Platform>
-    <ProjectGuid>f4ab9468-30d3-4547-9a7f-7a6b512b4086</ProjectGuid>
+    <ProjectGuid>{F4AB9468-30D3-4547-9A7F-7A6B512B4086}</ProjectGuid>
     <OutputType>Library</OutputType>
     <AppDesignerFolder>Properties</AppDesignerFolder>
     <RootNamespace>ClassLibrary2</RootNamespace>
@@ -31,22 +31,18 @@
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
   <ItemGroup>
-    <Reference Include="System"/>
-    
-    <Reference Include="System.Core"/>
-    <Reference Include="System.Xml.Linq"/>
-    <Reference Include="System.Data.DataSetExtensions"/>
-    
-    
-    <Reference Include="Microsoft.CSharp"/>
-    
-    <Reference Include="System.Data"/>
-    
-    <Reference Include="System.Xml"/>
+    <Reference Include="System" />
+    <Reference Include="System.Core" />
+    <Reference Include="System.Xml.Linq" />
+    <Reference Include="System.Data.DataSetExtensions" />
+    <Reference Include="Microsoft.CSharp" />
+    <Reference Include="System.Data" />
+    <Reference Include="System.Xml" />
   </ItemGroup>
   <ItemGroup>
     <Compile Include="Class1.cs" />
+    <Compile Include="Class2.cs" />
     <Compile Include="Properties\AssemblyInfo.cs" />
   </ItemGroup>
   <Import Project="$(MSBuildToolsPath)\Microsoft.CSharp.targets" />
- </Project>
+</Project>