.NET project SDKs

• 09/17/2020
• 6 minutes to read
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.NET Core and .NET 5.0 and later projects are associated with a software development kit (SDK). Each project SDK is a set of MSBuild targets and associated tasks that are responsible for compiling, packing, and publishing code. A project that references a project SDK is sometimes referred to as an SDK-style project.

Available SDKs

The following SDKs are available:

The .NET SDK is the base SDK for .NET. The other SDKs reference the .NET SDK, and projects that are associated with the other SDKs have all the .NET SDK properties available to them. The Web SDK, for example, depends on both the .NET SDK and the Razor SDK.

You can also author your own SDK that can be distributed via NuGet.

* Starting in .NET 5.0, Windows Forms and Windows Presentation Foundation (WPF) projects should specify the .NET SDK (Microsoft.NET.Sdk) instead of Microsoft.NET.Sdk.WindowsDesktop. For these projects, setting TargetFramework to net5.0-windows and UseWPF or UseWindowsForms to true will automatically import the Windows desktop SDK. If your project targets .NET 5.0 or later and specifies the Microsoft.NET.Sdk.WindowsDesktop SDK, you'll get build warning NETSDK1137.

Project files

.NET projects are based on the MSBuild format. Project files, which have extensions like .csproj for C# projects and .fsproj for F# projects, are in XML format. The root element of an MSBuild project file is the Project element. The Project element has an optional Sdk attribute that specifies which SDK (and version) to use. To use the .NET tools and build your code, set the Sdk attribute to one of the IDs in the Available SDKs table.

<Project Sdk="Microsoft.NET.Sdk">
  ...
</Project>

To specify an SDK that comes from NuGet, include the version at the end of the name, or specify the name and version in the global.json file.

<Project Sdk="MSBuild.Sdk.Extras/2.0.54">
  ...
</Project>

Another way to specify the SDK is with the top-level Sdk element:

<Project>
  <Sdk Name="Microsoft.NET.Sdk" />
  ...
</Project>

Referencing an SDK in one of these ways greatly simplifies project files for .NET. While evaluating the project, MSBuild adds implicit imports for Sdk.props at the top of the project file and Sdk.targets at the bottom.

<Project>
  <!-- Implicit top import -->
  <Import Project="Sdk.props" Sdk="Microsoft.NET.Sdk" />
  ...
  <!-- Implicit bottom import -->
  <Import Project="Sdk.targets" Sdk="Microsoft.NET.Sdk" />
</Project>

Preprocess the project file

You can see the fully expanded project as MSBuild sees it after the SDK and its targets are included by using the dotnet msbuild -preprocess command. The preprocess switch of the dotnet msbuild command shows which files are imported, their sources, and their contributions to the build without actually building the project.

If the project has multiple target frameworks, focus the results of the command on only one framework by specifying it as an MSBuild property. For example:

dotnet msbuild -property:TargetFramework=netcoreapp2.0 -preprocess:output.xml

Default includes and excludes

The default includes and excludes for Compile items, embedded resources, and None items are defined in the SDK. Unlike non-SDK .NET Framework projects, you don't need to specify these items in your project file, because the defaults cover most common use cases. This behavior makes the project file smaller and easier to understand and edit by hand, if needed.

The following table shows which elements and which globs are included and excluded in the .NET SDK:

Build errors

If you explicitly define any of these items in your project file, you're likely to get a "NETSDK1022" build error similar to the following:

Duplicate 'Compile' items were included. The .NET SDK includes 'Compile' items from your project directory by default. You can either remove these items from your project file, or set the 'EnableDefaultCompileItems' property to 'false' if you want to explicitly include them in your project file.

Duplicate 'EmbeddedResource' items were included. The .NET SDK includes 'EmbeddedResource' items from your project directory by default. You can either remove these items from your project file, or set the 'EnableDefaultEmbeddedResourceItems' property to 'false' if you want to explicitly include them in your project file.

To resolve the errors, do one of the following:

• Remove the explicit Compile, EmbeddedResource, or None items that match the implicit ones listed on the previous table.

• Set the EnableDefaultItems property to false to disable all implicit file inclusion:

  <PropertyGroup>
    <EnableDefaultItems>false</EnableDefaultItems>
  </PropertyGroup>
  

  If you want to specify files to be published with your app, you can still use the known MSBuild mechanisms for that, for example, the Content element.

• Selectively disable only Compile, EmbeddedResource, or None globs by setting the EnableDefaultCompileItems, EnableDefaultEmbeddedResourceItems, or EnableDefaultNoneItems property to false:

  <PropertyGroup>
    <EnableDefaultCompileItems>false</EnableDefaultCompileItems>
    <EnableDefaultEmbeddedResourceItems>false</EnableDefaultEmbeddedResourceItems>
    <EnableDefaultNoneItems>false</EnableDefaultNoneItems>
  </PropertyGroup>
  

  If you only disable Compile globs, Solution Explorer in Visual Studio still shows *.cs items as part of the project, included as None items. To disable the implicit None glob, set EnableDefaultNoneItems to false too.

Build events

In SDK-style projects, use an MSBuild target named PreBuild or PostBuild and set the BeforeTargets property for PreBuild or the AfterTargets property for PostBuild.

<Target Name="PreBuild" BeforeTargets="PreBuildEvent">
    <Exec Command="&quot;$(ProjectDir)PreBuildEvent.bat&quot; &quot;$(ProjectDir)..\&quot; &quot;$(ProjectDir)&quot; &quot;$(TargetDir)&quot;" />
</Target>

<Target Name="PostBuild" AfterTargets="PostBuildEvent">
   <Exec Command="echo Output written to $(TargetDir)" />
</Target>

<PropertyGroup>
  <PreBuildEvent>"$(ProjectDir)PreBuildEvent.bat" "$(ProjectDir)..\" "$(ProjectDir)" "$(TargetDir)"</PreBuildEvent>
</PropertyGroup>

Customize the build

There are various ways to customize a build. You may want to override a property by passing it as an argument to an msbuild or dotnet command. You can also add the property to the project file or to a Directory.Build.props file. For a list of useful properties for .NET projects, see MSBuild reference for .NET SDK projects.

Custom targets

.NET projects can package custom MSBuild targets and properties for use by projects that consume the package. Use this type of extensibility when you want to:

• Extend the build process.
• Access artifacts of the build process, such as generated files.
• Inspect the configuration under which the build is invoked.

You add custom build targets or properties by placing files in the form <package_id>.targets or <package_id>.props (for example, Contoso.Utility.UsefulStuff.targets) in the build folder of the project.

The following XML is a snippet from a .csproj file that instructs the dotnet pack command what to package. The <ItemGroup Label="dotnet pack instructions"> element places the targets files into the build folder inside the package. The <Target Name="CollectRuntimeOutputs" BeforeTargets="_GetPackageFiles"> element places the assemblies and .json files into the build folder.

<Project Sdk="Microsoft.NET.Sdk">

  ...
  <ItemGroup Label="dotnet pack instructions">
    <Content Include="build\*.targets">
      <Pack>true</Pack>
      <PackagePath>build\</PackagePath>
    </Content>
  </ItemGroup>
  <Target Name="CollectRuntimeOutputs" BeforeTargets="_GetPackageFiles">
    <!-- Collect these items inside a target that runs after build but before packaging. -->
    <ItemGroup>
      <Content Include="$(OutputPath)\*.dll;$(OutputPath)\*.json">
        <Pack>true</Pack>
        <PackagePath>build\</PackagePath>
      </Content>
    </ItemGroup>
  </Target>
  ...

</Project>

To consume a custom target in your project, add a PackageReference element that points to the package and its version. Unlike the tools, the custom targets package is included in the consuming project's dependency closure.

You can configure how to use the custom target. Since it's an MSBuild target, it can depend on a given target, run after another target, or be manually invoked by using the dotnet msbuild -t:<target-name> command. However, to provide a better user experience, you can combine per-project tools and custom targets. In this scenario, the per-project tool accepts whatever parameters are needed and translates that into the required dotnet msbuild invocation that executes the target. You can see a sample of this kind of synergy on the MVP Summit 2016 Hackathon samples repo in the dotnet-packer project.

See also

• Install .NET Core
• How to use MSBuild project SDKs
• Package custom MSBuild targets and props with NuGet