When element (MSBuild)

Artikel
03/10/2023

Specifies a possible block of code for the Choose element to select.

<Project> <Choose> <When> <Choose> ... <Otherwise> <Choose> ...

Syntax

<When Condition="'StringA'=='StringB'">
    <PropertyGroup>... </PropertyGroup>
    <ItemGroup>... </ItemGroup>
    <Choose>... </Choose>
</When>

Attributes and elements

The following sections describe attributes, child elements, and parent elements.

Attributes

Attribute	Description
Condition	Required attribute. Condition to evaluate. For more information, see Conditions.

Child elements

Element	Description
Choose	Optional element. Evaluates child elements to select one section of code to execute. There may be zero or more `Choose` elements in a `When` element.
ItemGroup	Optional element. Contains a set of user-defined Item elements. There may be zero or more `ItemGroup` elements in a `When` element.
PropertyGroup	Optional element. Contains a set of user-defined Property elements. There may be zero or more `PropertyGroup` elements in a `When` element.

Parent elements

Element	Description
Choose element (MSBuild)	Evaluates child elements to select one section of code to execute.

Remarks

If the Condition attribute evaluates to true, the child ItemGroup and PropertyGroup elements of the When element are executed and all subsequent When elements are skipped.

The Choose, When, and Otherwise elements are used together to provide a way to select one section of code to execute out of a number of possible alternatives. For more information, see Conditional constructs.

Example

The following project uses the Choose element to select which set of property values in the When elements to set. If the Condition attributes of both When elements evaluate to false, the property values in the Otherwise element are set. When running the example, try passing in various property settings from the command line, such as msbuild myproj.proj -p:Configuration=Test;Platform=x86, and see what the output path looks like. The example supposes the requirement is to set certain properties for debug and release builds, including the output folder based on the bitness of the platform rather than the actual platform name, and also support the 'Test' and 'Retail' configurations, but treat 'Retail' as 'Release'.

<Project>
    <PropertyGroup>
       <Configuration Condition="$(Configuration) == ''">Debug</Configuration>
       <Platform Condition="$(Platform) == ''">x64</Platform>
    </PropertyGroup>

  <Choose>
     <When Condition="$(Configuration)=='Test'">
        <PropertyGroup>
            <DebugSymbols>true</DebugSymbols>
            <DebugType>full</DebugType>
            <Optimize>false</Optimize>
            <DefineConstants>DEBUG;TRACE</DefineConstants>
        </PropertyGroup>
        <Choose>
          <When Condition="$(Platform)=='x86' Or $(Platform) == 'ARM32'">
            <PropertyGroup>
                <OutputPath>.\bin\Test\32-bit\</OutputPath>
            </PropertyGroup>
          </When>
          <When Condition="$(Platform)=='x64' Or $(Platform) == 'ARM64'">
            <PropertyGroup>
                <OutputPath>.\bin\Test\64-bit\</OutputPath>
            </PropertyGroup>
          </When>
          <!-- For any other platform, use the platform name -->
          <Otherwise>
            <PropertyGroup>
              <OutputPath>.\bin\Test\$(Platform)\</OutputPath>
            </PropertyGroup>
          </Otherwise>
        </Choose>
      </When>
      <When Condition="$(Configuration)=='Retail' Or $(Configuration)=='Release'">
        <PropertyGroup>
            <DebugSymbols>false</DebugSymbols>
            <Optimize>true</Optimize>
            <DefineConstants>TRACE</DefineConstants>
        </PropertyGroup>
        <Choose>
          <When Condition="$(Platform)=='x86' Or $(Platform) == 'ARM32'">
             <PropertyGroup>
                <OutputPath>.\bin\Release\32-bit\</OutputPath>
             </PropertyGroup>
          </When>
          <When Condition="$(Platform)=='x64' Or $(Platform) == 'ARM64'">
             <PropertyGroup>
                <OutputPath>.\bin\Release\64-bit\</OutputPath>
             </PropertyGroup>
          </When>
          <!-- For any other platform, use the platform name -->
          <Otherwise>
            <PropertyGroup>
                <OutputPath>.\bin\Release\$(Platform)\</OutputPath>
            </PropertyGroup>
          </Otherwise>
        </Choose>
      </When>
      <!-- For any other configuration, use debug properties-->
      <Otherwise>
        <PropertyGroup>
            <DebugSymbols>true</DebugSymbols>
            <DebugType>full</DebugType>
            <Optimize>false</Optimize>
            <DefineConstants>DEBUG;TRACE</DefineConstants>
        </PropertyGroup>
        <Choose>
          <When Condition="$(Platform)=='x86' Or $(Platform)=='ARM32'">
            <PropertyGroup>
              <OutputPath>.\bin\$(Configuration)\32-bit\</OutputPath>
            </PropertyGroup>
          </When>
          <When Condition="$(Platform)=='x64' Or $(Platform)=='ARM64'">
            <PropertyGroup>
              <OutputPath>.\bin\$(Configuration)\64-bit\</OutputPath>
            </PropertyGroup>
          </When>
        </Choose>
       </Otherwise>
  </Choose>

  <Target Name="ShowProperties">
    <Message Text="DebugSymbols: $(DebugSymbols)"/>
    <Message Text="Optimize: $(Optimize)"/>
    <Message Text="DefineConstants: $(DefineConstants)"/>
    <Message Text="OutputPath: $(OutputPath)"/>
  </Target>
</Project>

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