Environment variables get lost between MSBuild projects

I have a .NET solution containing following projects:

• web application (WAP)
• web deployment (WDP, .wdproj)
• wix setup (WIX, .wixproj)

In the WDP I've used a custom MSBuild task (SetEnvVar) to set some env. variables for further use in the build process. After setting them I can use them without prob. in the WDP but in the WIX they are empty/undefined. The strange thing is that when I reference those env. vars in the WIX files (by using properties in .wxs or preproc vars in .wxi) I get the values as expected.

Do you have any idea why the env. vars get lost/are undefined in .wixproj?

By the way the (solution) build process is triggered from inside VS 2010.

Update

This is basically my task code:

Environment.SetEnvironmentVariable(this.Variable, this.Value);

Is a MSBuild solution build not one process?

Will MSBuild spawn a new process for 开发者_JAVA百科every project in the solution?

is it possible your SetEnvVar task sets the environment variables for a single process instead of globally (which it should do to be safe btw)? In that case, it's likely that the WIX thingie is started as a different process in some way, so with it's own private copy of the current global environment set.

Here are the significant parts of the project files:

WDP (.wdproj)

<Target Name="AfterBuild">
    <SetEnvVar Variable="MAJOR" Value="$(MajorNumber)" />
    <SetEnvVar Variable="MINOR" Value="$(MinorNumber)" />
    <SetEnvVar Variable="REVISION" Value="$(RevisionNumber)" />
    <SetEnvVar Variable="BUILD" Value="$(BuildNumber)" />        
</Target>

WIX (.wixproj)

<Target Name="AfterBuild">
    <Message Text="Major: $(MAJOR) Minor: $(MINOR) Revision: $(REVISION)" />
    <Move SourceFiles=".\bin\$(Configuration)\$(OutputName).msi" DestinationFiles=".\bin\$(Configuration)\Product_$(MAJOR).$(MINOR).$(REVISION).msi" />        
</Target>

The Message task's log output is "Major: Minor: Revision: " therefore MAJOR, MINOR and REVISION vars are not availabe to the WIX project and for that the MSI package name is Product_...msi.

The project build order is of course WAP -> WDP -> WIX.