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MSBuild inline tasks

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MSBuild tasks are typically created by compiling a class that implements the ITask interface. For more information, see Tasks.

Starting in .NET Framework version 4, you can create tasks inline in the project file. You do not have to create a separate assembly to host the task. This makes it easier to keep track of source code and easier to deploy the task. The source code is integrated into the script.

In MSBuild 15.8, the RoslynCodeTaskFactory was added which can create .NET Standard cross-platform inline tasks. If you need to use inline tasks on .NET Core, you must use the RoslynCodeTaskFactory.

The structure of an inline task

An inline task is contained by a UsingTask element. The inline task and the UsingTask element that contains it are typically included in a .targets file and imported into other project files as required. Here is a basic inline task. Notice that it does nothing.

<Project ToolsVersion="15.0" xmlns="http://schemas.microsoft.com/developer/msbuild/2003">
  <!-- This simple inline task does nothing. -->
  <UsingTask
    TaskName="DoNothing"
    TaskFactory="CodeTaskFactory"
    AssemblyFile="$(MSBuildToolsPath)\Microsoft.Build.Tasks.Core.dll" >
    <ParameterGroup />
    <Task>
      <Reference Include="" />
      <Using Namespace="" />
      <Code Type="Fragment" Language="cs">
      </Code>
    </Task>
  </UsingTask>
</Project>

The UsingTask element in the example has three attributes that describe the task and the inline task factory that compiles it.

  • The TaskName attribute names the task, in this case, DoNothing.

  • The TaskFactory attribute names the class that implements the inline task factory.

  • The AssemblyFile attribute gives the location of the inline task factory. Alternatively, you can use the AssemblyName attribute to specify the fully qualified name of the inline task factory class, which is typically located in $(MSBuildToolsPath)\Microsoft.Build.Tasks.Core.dll.

The remaining elements of the DoNothing task are empty and are provided to illustrate the order and structure of an inline task. A more robust example is presented later in this topic.

  • The ParameterGroup element is optional. When specified, it declares the parameters for the task. For more information about input and output parameters, see Input and output parameters later in this topic.

  • The Task element describes and contains the task source code.

  • The Reference element specifies references to the .NET assemblies that you are using in your code. This is equivalent to adding a reference to a project in Visual Studio. The Include attribute specifies the path of the referenced assembly.

  • The Using element lists the namespaces that you want to access. This resembles the Using statement in Visual C#. The Namespace attribute specifies the namespace to include.

Reference and Using elements are language-agnostic. Inline tasks can be written in any one of the supported .NET CodeDom languages, for example, Visual Basic or Visual C#.

Note

Elements contained by the Task element are specific to the task factory, in this case, the code task factory.

Code element

The last child element to appear within the Task element is the Code element. The Code element contains or locates the code that you want to be compiled into a task. What you put in the Code element depends on how you want to write the task.

The Language attribute specifies the language in which your code is written. Acceptable values are cs for C#, vb for Visual Basic.

The Type attribute specifies the type of code that is found in the Code element.

  • If the value of Type is Class, then the Code element contains code for a class that derives from the ITask interface.

  • If the value of Type is Method, then the code defines an override of the Execute method of the ITask interface.

  • If the value of Type is Fragment, then the code defines the contents of the Execute method, but not the signature or the return statement.

The code itself typically appears between a <![CDATA[ marker and a ]]> marker. Because the code is in a CDATA section, you do not have to worry about escaping reserved characters, for example, "<" or ">".

Alternatively, you can use the Source attribute of the Code element to specify the location of a file that contains the code for your task. The code in the source file must be of the type that is specified by the Type attribute. If the Source attribute is present, the default value of Type is Class. If Source is not present, the default value is Fragment.

Note

When defining the task class in the source file, the class name must agree with the TaskName attribute of the corresponding UsingTask element.

HelloWorld

Here is a more robust inline task. The HelloWorld task displays "Hello, world!" on the default error logging device, which is typically the system console or the Visual Studio Output window. The Reference element in the example is included just for illustration.

<Project ToolsVersion="15.0" xmlns="http://schemas.microsoft.com/developer/msbuild/2003">
  <!-- This simple inline task displays "Hello, world!" -->
  <UsingTask
    TaskName="HelloWorld"
    TaskFactory="CodeTaskFactory"
    AssemblyFile="$(MSBuildToolsPath)\Microsoft.Build.Tasks.Core.dll" >
    <ParameterGroup />
    <Task>
      <Reference Include="System.Xml"/>
      <Using Namespace="System"/>
      <Using Namespace="System.IO"/>
      <Code Type="Fragment" Language="cs">
<![CDATA[
// Display "Hello, world!"
Log.LogError("Hello, world!");
]]>
      </Code>
    </Task>
  </UsingTask>
</Project>

You could save the HelloWorld task in a file that is named HelloWorld.targets, and then invoke it from a project as follows.

<Project ToolsVersion="15.0" xmlns="http://schemas.microsoft.com/developer/msbuild/2003">
  <Import Project="HelloWorld.targets" />
  <Target Name="Hello">
    <HelloWorld />
  </Target>
</Project>

Input and output parameters

Inline task parameters are child elements of a ParameterGroup element. Every parameter takes the name of the element that defines it. The following code defines the parameter Text.

<ParameterGroup>
  <Text />
</ParameterGroup>

Parameters may have one or more of these attributes:

  • Required is an optional attribute that is false by default. If true, then the parameter is required and must be given a value before calling the task.

  • ParameterType is an optional attribute that is System.String by default. It may be set to any fully qualified type that is either an item or a value that can be converted to and from a string by using System.Convert.ChangeType. (In other words, any type that can be passed to and from an external task.)

  • Output is an optional attribute that is false by default. If true, then the parameter must be given a value before returning from the Execute method.

For example,

<ParameterGroup>
  <Expression Required="true" />
  <Files ParameterType="Microsoft.Build.Framework.ITaskItem[]" Required="true" />
  <Tally ParameterType="System.Int32" Output="true" />
</ParameterGroup>

defines these three parameters:

  • Expression is a required input parameter of type System.String.

  • Files is a required item list input parameter.

  • Tally is an output parameter of type System.Int32.

If the Code element has the Type attribute of Fragment or Method, then properties are automatically created for every parameter. Otherwise, properties must be explicitly declared in the task source code, and must exactly match their parameter definitions.

Example

The following inline task replaces every occurrence of a token in the given file with the given value.

<Project xmlns='http://schemas.microsoft.com/developer/msbuild/2003' ToolsVersion="15.0">

  <UsingTask TaskName="TokenReplace" TaskFactory="CodeTaskFactory" AssemblyFile="$(MSBuildToolsPath)\Microsoft.Build.Tasks.Core.dll">
    <ParameterGroup>
      <Path ParameterType="System.String" Required="true" />
      <Token ParameterType="System.String" Required="true" />
      <Replacement ParameterType="System.String" Required="true" />
    </ParameterGroup>
    <Task>
      <Code Type="Fragment" Language="cs"><![CDATA[
string content = File.ReadAllText(Path);
content = content.Replace(Token, Replacement);
File.WriteAllText(Path, content);

]]></Code>
    </Task>
  </UsingTask>

  <Target Name='Demo' >
    <TokenReplace Path="C:\Project\Target.config" Token="$MyToken$" Replacement="MyValue"/>
  </Target>
</Project>

See also