When Element (MSBuild)

Article
11/15/2016

Note

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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 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 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>