System.IO.FileInfo adds unexpected string to path when used in WIX Custom Action

I've got an WIX(V3.11.1) installer in which I'm creating an FileInfo based on value which is passed to Custom Action. Value which was passed to Custom Action is correct, session.CustomActionData["INSTALLFOLDER"] returns proper path, which is C:\Program Files(x86)\MyApplication.

Unfortunately, when I create FileInfo targetDir = new FileInfo(session.CustomActionData["INSTALLFOLDER"]), the result of targetDir.FullName is C:\Windows\Installer\MSIE335.tmp-\C:\Program Files(x86)\MyApplication\.

I've tried to find any information about how constructor of FileInfo works, but without any result. Do you have any ideas why C:\Windows\Installer\MSIE335.tmp-\ appears in FileInfo and how to create it with real path?

Code which is used by me to check all values:

string path = session.CustomActionData["INSTALLFOLDER"];

session.Log(path); //result is C:\Program Files(x86)\MyApplication
FileInfo targetDir = new FileInfo(path);

session.Log(targetDir.FullName); // result is C:\Windows\Installer\MSIE335.tmp-\C:\Program Files(x86)\MyApplication\

Solution

My setup-sense is guessing that the value of INSTALLFOLDER in your CustomActionData is actually the value [INSTALLFOLDER]. When logging, that syntax will get resolved to its proper value. That is why it looks good. However, what FileInfo is actually getting is a value like:

FileInfo targetDir = new FileInfo("[INSTALLFOLDER]");

Which of course is "The file named "[INSTALLFOLDER]" in the current directory". That matches your second log line.

The fix would be to ensure you're passing the value of INSTALLFOLDER in your CustomActionData. A few different ways to do that depending how you are scheduling your deferred custom action and setting the named property. For example, using SetProperty should be an easy way to fix it.

Update: Hawex provided a snippet that defined the custom action. It looked like:

<Property Id="CustomActionOnInstall" Value="INSTALLFOLDER=[INSTALLFOLDER]" />

<CustomAction Id="CustomActionOnInstall" BinaryKey="CustomActions" Execute="deferred" 
              Impersonate="no"  DllEntry="OnInstall" Return="check" />
<InstallExecuteSequence>
  <Custom Action="CustomActionOnInstall" Before="InstallFinalize">NOT Installed</Custom>      
</InstallExecuteSequence>

to fix, just change the static (unevaluated) Property to a SetProperty like so:

<SetProperty Id="CustomActionOnInstall" Value="INSTALLFOLDER=[INSTALLFOLDER]"
             Before="CustomActionOnInstall" Sequence="execute" />