Changing installation location based on condition - wix

Question

I am making installer for a utility that can be installed as part of a main program or independently. The location of the main program in present in a registry key. If the main program is installed, the utility should be installed in a "Utilities" sub-directory. e.g. D:\Program Files(x86)\MainProgram\Utilities. If the main program is not installed, then it should default to root drive folder e.g. C:\Program Files(x86)\MainProgram\Utilities.
Installation should get the registry key (e.g. HKLM\Software\MainProgram\ Key:"Install_location"). This will give a path till d:\Program File(x86)\MainProgram. The utility should be installed in its sub-directly. If the key is not present, it should default to the standard location.

Answer 1

Read the registry value from custom action using C# or some other language and check if key exists or else you can use WIX to find if registry key exists.
RegistryKey regKey = Microsoft.Win32.Registry.LocalMachine.OpenSubKey(#"Software\MainProgram\Key");
if ((string)Registry.GetValue(regKey, "Install_location", "0") != "0")
{
session["Somevariable"] = (string)Registry.GetValue(regKey, "Install_location")
}
using WIX
<Property Id="INSTALLLOCATION">
<RegistrySearch Id="INSTALLLOCATION"
Name="Install_location"
Root="HKLM"
Key="Software\MainProgram\Key"
Type="raw" />
</Property>
On the basis of the value of WIX session variable you can decide the install location and install the utility at the desired path.

Answer 2

Read the MainProgram location into a property:
<Property Id="MainProgramDir">
<RegistrySearch Id="FindMainProgramDir"
Root="HKLM"
Key="Software\MainProgram"
Name="Install_location"
Type="directory" />
</Property>
And set up your directory structure for the default behavior:
<Directory Id="TARGETDIR" Name="SourceDir">
<Directory Id="ProgramFilesFolder">
<Directory Id="MainProgramDir" Name="MainProgram">
<Directory Id="INSTALLDIR" Name="Utilities"/>
</Directory>
</Directory>
</Directory>
Directory elements are like properties, and will be overridden if there is a property with the same Id. If the property is not set (because the RegistrySearch fails) then it will be as it was defined in the directory structure you set up.