.NET 8自定义MSBuild任务加载失败：无法找到System.Runtime程序集

错误信息 #

MSB4062 The "HitcMacroTest.PreprocessTask" task could not be loaded from the assembly
\bin\Debug\net8.0-windows\HitcMacroTest.dll. Could not load file or assembly
'System.Runtime, Version=8.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a' or 
one of its dependencies. The system cannot find the file specified. Confirm that the 
<UsingTask> declaration is correct, that the assembly and all its dependencies are 
available, and that the task contains a public class that implements 
Microsoft.Build.Framework.ITask. 
WinFormsApp1    \Macro\WinFormsApp1\WinFormsApp1.csproj 28  

项目环境 #

HitcMacroTest（自定义MSBuild任务项目）与WinFormsApp1（目标项目）均以**.NET 8.0**为目标框架，WinFormsApp1的csproj配置如下：

<ItemGroup>
<PackageReference Include="Microsoft.Build.Utilities.Core" Version="17.10.4" />
</ItemGroup>

<UsingTask TaskName="HitcMacroTest.PreprocessTask" AssemblyFile="F:\PROJECTS\Macro\WinFormsApp1\bin\Debug\net8.0-windows\HitcMacroTest.dll" />

<ItemGroup>
<PreprocessSources Include="F:\PROJECTS\Macro\**\*.cs" Exclude="$(PreprocessedOutputDirectory)\**\*" />
</ItemGroup>

<ItemGroup>
<ProjectReference Include="..\HitcMacroTest\HitcMacroTest.csproj" />
</ItemGroup>

<Target Name="PreprocessMacros" BeforeTargets="BeforeBuild">
<MakeDir Directories="$(PreprocessedOutputDirectory)" />
<PreprocessTask InputFiles="@(PreprocessSources)" 
OutputDirectory="$(PreprocessedOutputDirectory)" />
<ItemGroup>
<Compile Remove="@(PreprocessSources)" />
<Compile Include="$(PreprocessedOutputDirectory)\**\*.cs" />
</ItemGroup>
</Target>

解决方法 #

1. 修正程序集引用路径，确保构建顺序 #

当前AssemblyFile硬编码了WinFormsApp1的输出目录，但HitcMacroTest的程序集可能未被复制到该目录，或者路径存在问题。改用项目引用的输出路径变量，同时确保HitcMacroTest先于WinFormsApp1构建：

<!-- 替换原UsingTask节点 -->
<UsingTask TaskName="HitcMacroTest.PreprocessTask" AssemblyFile="$(SolutionDir)HitcMacroTest\bin\$(Configuration)\net8.0\HitcMacroTest.dll" />

注：$(SolutionDir)为MSBuild内置变量，自动指向解决方案根目录，避免硬编码绝对路径。

2. 调整自定义任务项目的目标框架 #

MSBuild默认基于.NET Framework运行，直接加载.NET 8程序集可能出现依赖缺失。可将HitcMacroTest的目标框架改为**.NET Standard 2.0或.NET Framework 4.7.2**，同时匹配兼容版本的Microsoft.Build.Utilities.Core包：

• 修改HitcMacroTest.csproj的目标框架：

  <TargetFramework>net472</TargetFramework>
  

• 安装对应版本的NuGet包：Microsoft.Build.Utilities.Core 16.11.0（适配.NET Framework）

3. 使用.NET Core MSBuild构建 #

通过dotnet build命令构建项目，该命令使用.NET Core版本的MSBuild，能更好地兼容.NET 8程序集的依赖加载：

dotnet build WinFormsApp1.csproj -c Debug

4. 验证自定义任务类的实现 #

确保PreprocessTask是public类，且正确实现ITask接口（继承Microsoft.Build.Utilities.Task更简便）：

using Microsoft.Build.Utilities;
using Microsoft.Build.Framework;

public class PreprocessTask : Task
{
    [Required]
    public ITaskItem[] InputFiles { get; set; }

    [Required]
    public string OutputDirectory { get; set; }

    public override bool Execute()
    {
        // 任务逻辑实现
        return true;
    }
}

5. 确保依赖库复制到输出目录 #

在HitcMacroTest项目中，设置所有NuGet依赖的CopyLocal为true，确保依赖库被复制到输出目录，供MSBuild加载时使用。

内容的提问来源于stack exchange，提问作者pramod maurya