[SOLVED] test if an MSBuild property is defined?

test if an MSBuild property is defined?

In MsBuild, is it possible to create an MSBuild condition (or another situation) that will evaluate whether a Property is 'defined' (presuming that this is previous to assigning the property a value somewhere)?

The following seems a little too clumsy to be reliable:

<PropertyGroup Label="Undefined State">
     <Defined></Defined>
</PropertyGroup>

<Choose>
   <When Condition="('$(Defined)' == '' OR '$(Defined)' != '')">
        <Message Text="Defined is probably/likely/assuredly defined"/>
    </When>
    <Otherwise>
       <Message Text="Defined is reportedly/maybe/possibly not defined"/>
    </Otherwise>
<Choose>

Solution

There exists common method for overriding properties.

Sample from C:\Windows\Microsoft.NET\Framework\v4.0.30319\Microsoft.Common.targets

   <PropertyGroup>
       <TargetFrameworkIdentifier Condition="'$(TargetFrameworkIdentifier)' == ''">.NETFramework</TargetFrameworkIdentifier>
       <TargetFrameworkVersion Condition=" '$(TargetFrameworkVersion)' == '' ">v4.0</TargetFrameworkVersion>
   </PropertyGroup>

If you will try to get value from $(NeverDefinedProperty) you just get an empty string. Can you describe the problem you want to solve?