[wix-users] Unable to correctly specify a variable for WiX within Visual Studio

[Jon Earle]

Setup is Wix 3.10.2 and visual studio 2015. Working with a wix setup project and custom action project.
I want to create a fragment containing the javados for my project. I had read (http://weblogs.sqlteam.com/mladenp/archive/2010/02/11/WiX-3-Tutorial-SolutionProject-structure-and-Dev-resources.aspx) to set a pre-processor variable (or system variable). I opted to include the variable definition in the project. I tried the pre-processor var
<DefineConstants>JavaDocBase=c:\javadocs</DefineConstants>
and just setting a normal variable:
<WixVariables>JavaDocBase=c:\javadocs</WixVariables>
Neither ended up working.
Pre-Build event:
<PropertyGroup><PreBuildEvent>"$(WIX)bin\heat.exe" dir "$(var.JavaDocBase)" -cg JavaDocs_JSP -gg -scom -sreg -sfrag -srd -dr INSTALLDIR -var var.JavaDocBase -out "$(ProjectDir)\JavaDocs_JSP_Fragment.wxs"</PreBuildEvent></PropertyGroup>  
I always seem to receive the error:
Unhandled Exception:The expression """.JavaDocBase" cannot be evaluated. Method 'System.String.JavaDocBase' not found.
I have tried var.JavaDocBase, wix.JavaDocBase, env.JavaDocBase and Just JavaDocBase... while the last will allow the command to run, it doesn't put in the proper path so I am no further ahead.
Is it possible to replicate what is in that previously linked tutorial and if so, what have I done wrong?