Question

I’m trying to set a default value for an MSBuild property. Say I start with this:

<Choose>
    <When Condition="..something..">
        <PropertyGroup>
            ...
            <MySetting>true</MySetting>
        <PropertyGroup>
    </When>
    ...
</Choose>

If the condition is not true, then MySetting will be ”. So shouldn’t this set it to false?

<PropertyGroup>
    <MySetting Condition="'$(MySetting)'==''">false</MySetting>
</PropertyGroup>

Later on, I’d like to use MySetting in a conditional without having to test for ==’true’, like this:

<PropertyGroup Condition="$(MySetting)">
    ...
</PropertyGroup>

Yet when I load this project into Visual Studio it complains that the specified condition “$(MySetting)” evaluates to “” instead of a boolean.

So it appears that either my condition that checks for ” to assign the property to false is incorrect. What am I doing wrong?

Answer 1

In MSBuild, you’re dealing with strings so you get the '' instead of false…if you want to default it to 'false' and override via the command line, just declare a property group above your existing condition block in the script:

<PropertyGroup>
    <MySetting>false</MySetting>
</PropertyGroup>

Your condition block below can set this to true, or you could also set it via the command line, like this:

MSBuild.exe MyMSBuildFile.csproj /p:MySetting=true