How to inspect a CustomAction's property (Wix)? - wix

Question

I am trying to put together a small 'prerequisites' dialog in Wix to give confidence to the users that they have all of the required things needed to run my software:
For example, I have a need for Managed DirectX, so I look for some DLLs:
<Property Id="MANAGED_DIRECTX">
<DirectorySearch Path="$(env.SystemRoot)\Microsoft.NET\DirectX for Managed Code\1.0.2902.0" Depth="0" Id="MDXDir">
<FileSearch Name="Microsoft.DirectX.dll"/>
</DirectorySearch>
</Property>
<Property Id="MANAGED_DIRECTX_DIRECTINPUT">
<DirectorySearch Path="$(env.SystemRoot)\Microsoft.NET\DirectX for Managed Code\1.0.2902.0" Depth="0" Id="MDXInputDir">
<FileSearch Name="Microsoft.DirectX.DirectInput.dll"/>
</DirectorySearch>
</Property>
I also have a CustomAction to combine my condition logic:
<CustomAction Id="SetManagedDirectXInstalled"
Property="MANAGED_DIRECTX_INSTALLED"
Value="NOT([MANAGED_DIRECTX] = '') AND NOT ([MANAGED_DIRECTX_DIRECTINPUT] = ''")/>
This CustomAction is sequenced:
<InstallExecuteSequence>
<Custom Action="SetManagedDirectXInstalled" After="AppSearch" />
<RemoveExistingProducts After="InstallInitialize" />
</InstallExecuteSequence>
What I should now be able to do is use "MANAGED DIRECTX INSTALLED" to do something, e.g.
<Control Id="NoManagedDirectX" Type="Text" X="20" Y="50" Width="300" Height="60" Transparent="yes" NoPrefix="yes" Hidden="yes">
<Text>Microsoft Managed DirectX (MDX) for DirectX 9.0 is NOT installed</Text>
<Condition Action="show">NOT MANAGED_DIRECTX_INSTALLED</Condition>
</Control>
<Control Id="ManagedDirectX" Type="Text" X="20" Y="50" Width="300" Height="60" Transparent="yes" NoPrefix="yes" Hidden="yes">
<Text>Microsoft Managed DirectX (MDX) for DirectX 9.0 is correctly installed</Text>
<Condition Action="show">MANAGED_DIRECTX_INSTALLED</Condition>
</Control>
It doesn't matter what I do, the condition is always false (e.g. not installed) even when I know the files are there. Using the msiexec command with /l*vx does not show the MANAGED DIRECTX INSTALLED property anywhere.
When a <Condition> is used with the following, it successfully prevents installation (although I no longer want to block installs in this case, just advise).
<Condition Message="You must have Microsoft Managed DirectX (MDX) for DirectX 9.0 installed">
MANAGED_DIRECTX AND MANAGED_DIRECTX_DIRECTINPUT
</Condition>
How can I trace/debug this (or what have I done wrong?)
EDIT - I'm now certain that my CustomAction is not even being called, setting it to the following is not showing expected results either!
<CustomAction Id='SetManagedDirectXInstalled'
Property='MANAGED_DIRECTX_INSTALLED'
Value='Something hard-coded'/>
or
<CustomAction Id='SetManagedDirectXInstalled'
Error='Some error should show!'/>

Answer 1

I think I may have found the answer, but I can't try it until I'm next at my development PC.
It appears I have to compare the values to TRUE/FALSE (or empty string) not just expecting it to work as boolean (Source)
In these expressions, you can use
property names (remember that they are
case sensitive). Non-existent property
names will be treated as empty
strings. The logical value of a
property reflects whether it has been
set—meaning that you cannot check for
a logical value by simply using the
property:
PROPERTY
This will evaluate to true if the property has been set and has any
value, even if this value is false.
NOT PROPERTY
This will evaluate to true if the property has not been set at all.
PROPERTY = TRUE
PROPERTY = FALSE
This is the proper way to check the value of a logical property.

Answer 2

To debug, use a verbose log file. It will show you the states of your Properties as they change. You should then be able to evaluate the Condition with that knowledge
I answered this same question not too long ago here. A Condition that uses the Property name is a test for existence. An existence test for a Property evaluates to true if the Property has any value at all. If you want to check the value of a Property you need to do so explicitly.