When Element (MSBuild)

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

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

<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 MSBuild 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 an 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 MSBuild 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.

<Project
    xmlns="https://schemas.microsoft.com/developer/msbuild/2003" >
    <PropertyGroup>
        <Configuration Condition="'$(Configuration)' == ''">Debug</Configuration>
        <OutputType>Exe</OutputType>
        <RootNamespace>ConsoleApplication1</RootNamespace>
        <AssemblyName>ConsoleApplication1</AssemblyName>
        <WarningLevel>4</WarningLevel>
    </PropertyGroup>
    <Choose>
        <When Condition=" '$(Configuration)'=='debug' ">
            <PropertyGroup>
                <DebugSymbols>true</DebugSymbols>
                <DebugType>full</DebugType>
                <Optimize>false</Optimize>
                <OutputPath>.\bin\Debug\</OutputPath>
                <DefineConstants>DEBUG;TRACE</DefineConstants>
            </PropertyGroup>
            <ItemGroup>
                <Compile Include="UnitTesting\*.cs" />
                <Reference Include="NUnit.dll" />
            </ItemGroup>
        </When>
        <When Condition=" '$(Configuration)'=='retail' ">
            <PropertyGroup>
                <DebugSymbols>false</DebugSymbols>
                <Optimize>true</Optimize>
                <OutputPath>.\bin\Release\</OutputPath>
                <DefineConstants>TRACE</DefineConstants>
            </PropertyGroup>
        </When>
        <Otherwise>
            <PropertyGroup>
                <DebugSymbols>true</DebugSymbols>
                <Optimize>false</Optimize>
                <OutputPath>.\bin\$(Configuration)\</OutputPath>
                <DefineConstants>DEBUG;TRACE</DefineConstants>
            </PropertyGroup>
        </Otherwise>
    </Choose>
    <Import Project="$(MSBuildBinPath)\Microsoft.CSharp.targets" />
</Project>

See Also

Reference

MSBuild Conditional Constructs

Concepts

MSBuild Project File Schema Reference