.NET project SDKs

Articol
10/15/2024

Modern .NET projects are associated with a project 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:

ID	Description	Repo
`Microsoft.NET.Sdk`	The .NET SDK	https://github.com/dotnet/sdk
`Microsoft.NET.Sdk.Web`	The .NET Web SDK	https://github.com/dotnet/sdk
`Microsoft.NET.Sdk.Razor`	The .NET Razor SDK	https://github.com/dotnet/aspnetcore
`Microsoft.NET.Sdk.BlazorWebAssembly`	The .NET Blazor WebAssembly SDK	https://github.com/dotnet/aspnetcore
`Microsoft.NET.Sdk.Worker`	The .NET Worker Service SDK
`Aspire.AppHost.Sdk`	The .NET Aspire SDK	https://github.com/dotnet/aspire
`MSTest.Sdk`	The MSTest SDK	https://github.com/microsoft/testfx

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.

For Windows Forms and Windows Presentation Foundation (WPF) projects, you specify the .NET SDK (Microsoft.NET.Sdk) and set some additional properties in the project file. For more information, see Enable .NET Desktop SDK.

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>

Starting with .NET Aspire 9, the preceding example could instead use the .NET Aspire SDK.

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

    <Sdk Name="Aspire.AppHost.Sdk" Version="9.0.0-rc.1.24511.1" />
    <!-- Omitted for brevity... -->

</Project>

For more information, see .NET Aspire tooling and setup.

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>

Tip

On a Windows machine, the Sdk.props and Sdk.targets files can be found in the %ProgramFiles%\dotnet\sdk\[version]\Sdks\Microsoft.NET.Sdk\Sdk folder.

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=net8.0 -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:

Element	Include glob	Exclude glob	Remove glob
Compile	*/.cs (or other language extensions)	*/.user; */.proj; /.sln; */.vssscc	N/A
EmbeddedResource	*/.resx	*/.user; */.proj; /.sln; */.vssscc	N/A
None	*/	*/.user; */.proj; /.sln; */.vssscc	*/.cs; */.resx

Note

The ./bin and ./obj folders, which are represented by the $(BaseOutputPath) and $(BaseIntermediateOutputPath) MSBuild properties, are excluded from the globs by default. Excludes are represented by the DefaultItemExcludes property.

The .NET Desktop SDK has additional includes and excludes for WPF. For more information, see WPF default includes and excludes.

If you explicitly define any of these items in your project file, you're likely to get a NETSDK1022 build error. For information about how to resolve the error, see NETSDK1022: Duplicate items were included.

Implicit using directives

Starting in .NET 6, implicit global using directives are added to new C# projects. This means that you can use types defined in these namespaces without having to specify their fully qualified name or manually add a using directive. The implicit aspect refers to the fact that the global using directives are added to a generated file in the project's obj directory.

Implicit global using directives are added for projects that use one of the following SDKs:

Microsoft.NET.Sdk
Microsoft.NET.Sdk.Web
Microsoft.NET.Sdk.Worker
Microsoft.NET.Sdk.WindowsDesktop

A global using directive is added for each namespace in a set of default namespaces that are based on the project's SDK. These default namespaces are shown in the following table.

SDK	Default namespaces
Microsoft.NET.Sdk	System System.Collections.Generic System.IO System.Linq System.Net.Http System.Threading System.Threading.Tasks
Microsoft.NET.Sdk.Web	Microsoft.NET.Sdk namespaces System.Net.Http.Json Microsoft.AspNetCore.Builder Microsoft.AspNetCore.Hosting Microsoft.AspNetCore.Http Microsoft.AspNetCore.Routing Microsoft.Extensions.Configuration Microsoft.Extensions.DependencyInjection Microsoft.Extensions.Hosting Microsoft.Extensions.Logging
Microsoft.NET.Sdk.Worker	Microsoft.NET.Sdk namespaces Microsoft.Extensions.Configuration Microsoft.Extensions.DependencyInjection Microsoft.Extensions.Hosting Microsoft.Extensions.Logging
Microsoft.NET.Sdk.WindowsDesktop (Windows Forms)	Microsoft.NET.Sdk namespaces System.Drawing System.Windows.Forms
Microsoft.NET.Sdk.WindowsDesktop (WPF)	Microsoft.NET.Sdk namespaces Removed System.IO Removed System.Net.Http

If you want to disable this feature, or if you want to enable implicit global using directives in an existing C# project, you can do so via the ImplicitUsings MSBuild property.

You can specify additional implicit global using directives by adding Using items (or Import items for Visual Basic projects) to your project file, for example:

<ItemGroup>
  <Using Include="System.IO.Pipes" />
</ItemGroup>

Implicit package references

When your project targets .NET Standard 1.0-2.0, the .NET SDK adds implicit references to certain metapackages. A metapackage is a framework-based package that consists only of dependencies on other packages. Metapackages are implicitly referenced based on the target frameworks specified in the TargetFramework or TargetFrameworks (plural) property of your project file.

<PropertyGroup>
  <TargetFramework>netstandard2.0</TargetFramework>
</PropertyGroup>

<PropertyGroup>
  <TargetFrameworks>netstandard2.0;net462</TargetFrameworks>
</PropertyGroup>

If needed, you can disable implicit package references using the DisableImplicitFrameworkReferences property, and add explicit references to just the frameworks or packages you need.

Recommendations:

When targeting .NET Framework or .NET Standard 1.0-2.0, don't add an explicit reference to the NETStandard.Library metapackages via a <PackageReference> item in your project file. For .NET Standard 1.0-2.0 projects, these metapackages are implicitly referenced. For .NET Framework projects, if any version of NETStandard.Library is needed when using a .NET Standard-based NuGet package, NuGet automatically installs that version.
If you need a specific version of the NETStandard.Library metapackage when targeting .NET Standard 1.0-2.0, you can use the <NetStandardImplicitPackageVersion> property and set the version you need.

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>

Note

You can use any name for the MSBuild targets. However, the Visual Studio IDE recognizes PreBuild and PostBuild targets, so by using those names, you can edit the commands in the IDE.
The properties PreBuildEvent and PostBuildEvent are not recommended in SDK-style projects, because macros such as $(ProjectDir) aren't resolved. For example, the following code is not supported:

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

Customize the build

There are various ways to customize a build. You might want to override a property by passing it as an argument to the 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.

Tip

An easy way to create a new Directory.Build.props file from the command line is by using the command dotnet new buildprops at the root of your repository.

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.

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