Wix error undefined preprocessor variable(error CNDL0150) - wix

Question

I am trying to build my first installer using WIX. I am not using visual studio instead i am using command line. I have a wxs file and i have also created a .wxi file for the Headers and i have defined them buy i get the following error when i run the candle.exe "Undefined preprocessor variable '$(var.ProjectDir)'"
Here is the .wxs and .wxi
<?xml version="1.0" encoding="UTF-8"?>
<Wix xmlns="http://schemas.microsoft.com/wix/2006/wi">
<Product Id="{CB06C559-BCBF-4C85-95F3-FE55F6F50463}" Name="My first msi installer" Language="1033" Version="1.0.0.0" Manufacturer="Wave-axis" UpgradeCode="9be991bb-ceb1-4320-bfc7-56738e32c99a">
<Package InstallerVersion="200" Compressed="yes" InstallScope="perMachine" />
<Icon Id="icon.ico" SourceFile="$(var.ProjectDir)icon.ico" />
<Property Id="WAVEAXIS" Value="icon.ico" />
<MajorUpgrade DowngradeErrorMessage="A newer version of [ProductName] is already installed." />
<MediaTemplate />
<UIRef Id="WixUI_Minimal" />
<!--used for the UI for the installer-->
<Feature Id="ProductFeature" Title="My first msi installer" Level="1">
<!-- This includes all the feature of the installer-->
<ComponentGroupRef Id="ProductComponents" />
<ComponentRef Id="ApplicationShortcut" />
<!--Used for shortcut on the start up menu-->
<ComponentRef Id="ApplicationShortcutDesktop" />
<!--used for desktop shortcut-->
</Feature>
</Product>
<Fragment>
<Directory Id="TARGETDIR" Name="SourceDir">
<Directory Id="ProgramFilesFolder">
<!--install location of the application-->
<Directory Id="INSTALLFOLDER" Name="My first msi installer" />
</Directory>
<Directory Id="ProgramMenuFolder">
<!--install location for the startup-->
<Directory Id="ApplicationProgramsFolder" Name="My first msi installer" />
</Directory>
<Directory Id="DesktopFolder" Name="Desktop" />
<!--install loaction for the desktop-->
</Directory>
</Fragment>
</Wix>
.wxi code
<?xml version="1.0" encoding="utf-8"?>
<Include xmlns="http://schemas.microsoft.com/wix/2006/wi">
<?define firstapplication.TargetDir ?>
<?define ProjectDir ?>
<?define firstapplication_TargetDir ?>
<?define ProductId=652648517 ?>
</Include>
regards Sagar

Answer 1

You need to include your wxi file in every wxs file you wish to use the properties in at the top of your file before the <Wix> tag
<?include $(sys.SOURCEFILEDIR)Path\to\InstallVars.wxi?>
<Wix xmlns="http://...">
...
</Wix>
This page will explain some of the available variables for the preprocessor like "SOURCEFILEDIR".