MSBuild overwrite properties value with Import - msbuild

Question

I have a msbuild script which contains only PropertyGroup: DefaultVariables.msbuild
<Project xmlns="http://schemas.microsoft.com/developer/msbuild/2003">
<!-- default values if nothing is set in Main.proj -->
<PropertyGroup>
<ProjectName Condition="'$(PublishService)'==''">DefaultService</ProjectName>
</PropertyGroup>
</Project>
The PublishService can be changed depend on environment.
I also have a Variables.msbuild with is same with above script, except the service name:
<Project xmlns="http://schemas.microsoft.com/developer/msbuild/2003">
<!-- default values if nothing is set in Main.proj -->
<PropertyGroup>
<ProjectName Condition="'$(PublishService)'==''">ErpService</ProjectName>
</PropertyGroup>
</Project
My main build script: BuildMsi.msbuild import the DefaultVariables.msbuild and has a target CreateEnvironmentSpecificInstaller which calls to Msi.msbuild
<Project xmlns="http://schemas.microsoft.com/developer/msbuild/2003" DefaultTargets="CreateInstaller">
<PropertyGroup>
<BaseDir Condition="$(BaseDir)==''">$(MSBuildProjectDirectory)</BaseDir>
</PropertyGroup>
<Import Project="DefaultVariables.msbuild" />
<!-- Something else -->
<Target Name="CreateEnvironmentSpecificInstaller" DependsOnTargets="$(SpecificBuildSteps)">
<MSBuild Projects="$(RedistDir)\Framework\Msi.msbuild" Targets="CreateBatchScripts" StopOnFirstFailure="true" Properties="Configuration=$(Configuration)" RebaseOutputs="true" />
</Target>
<Target Name="CreateInstaller" DependsOnTargets="PrintVersion;$(GenericBuildSteps)">
<MSBuild Condition=" '$(EnvironmentName)' == '**AllEnvironments**' " Projects="$(BaseDir)\$(BtsDeploymentFrameworkDir)\BuildMsi.msbuild" Targets="CreateEnvironmentSpecificInstaller" StopOnFirstFailure="true"
Properties="Configuration=$(Configuration);" RebaseOutputs="true" />
<CallTarget Targets="RemoveGeneratedEnvironmentSettings" />
</Target>
</Project>
In Msi.msbuild script I add an Import to Variables.msbuild script, but the PublishService after this is still the DefaultService:
<Project xmlns="http://schemas.microsoft.com/developer/msbuild/2003" DefaultTargets="CreateInstaller">
<Import Project="Variables.msbuild" />
<Target Name="CreateBatchScripts">
<Message Text="PublishService = $(PublishService)" />
</Target>
</Project>
How can I overwrite this property value in runtime?

Answer 1

First of all, you are never giving a value to PublishService. I assume in DefaultVariables.msbuild what you wanted to do is
<Project xmlns="http://schemas.microsoft.com/developer/msbuild/2003">
<!-- default values if nothing is set in Main.proj -->
<PropertyGroup>
<PublishService> Condition="'$(PublishService)'==''">DefaultService</PublishService>
</PropertyGroup>
</Project>
Then, I suggest you also rename the property in Variables.msbuild and remove the condition Condition="'$(PublishService)'==''. As you have given the property a default value in DefaultVariables.msbuild, the condition will not be fulfilled and thus the value will not be changed.
<Project xmlns="http://schemas.microsoft.com/developer/msbuild/2003">
<PropertyGroup>
<PublishService>ErpService</PublishService>
</PropertyGroup>
</Project>