How to Obtain the MSI 'UILevel' Property From a C++ Custom Action - c++

Question

I am trying to get at the 'UILevel' MSI property from within a C++ custom action in order to determine whether or not the user is running in 'no UI mode', but am not having much luck. The function I am calling is passed the MSIHANDLE from a function which I export in my DLL (which may be either a 'deferred' or 'firstsequence' action). What I'm seeing is that MsiGetPropertyW is always returning ERROR_MORE_DATA and the trueLength field is always 0. Here is my code:
bool runningInNoUIMode(MSIHANDLE hInstall)
{
unsigned long nBufLen = 64UL;
WCHAR *wszValue = new WCHAR[nBufLen];
DWORD trueLength = 0UL;
UINT result = ::MsiGetPropertyW(hInstall, L"UILevel", L"", &trueLength); // Get the size of the property value first to see if there is enough storage allocated.
if (ERROR_MORE_DATA == result || nBufLen <= trueLength)
{
if (NULL != wszValue)
{
delete [] wszValue;
}
// Allocate more memory for the property adding one for the null terminator.
nBufLen = trueLength + 1;
wszValue = new WCHAR[nBufLen];
}
if (NULL == wszValue)
{
WcaLog(LOGMSG_STANDARD, "Unable to determine the user interface level the MSI is being run with because we were unable to allocate storage for accessing the 'UILevel' property.");
return false;
}
memset(wszValue, L'\0', nBufLen * sizeof(WCHAR));
result = ::MsiGetPropertyW(hInstall, L"UILevel", wszValue, &trueLength);
if (ERROR_SUCCESS != result)
{
WcaLog(LOGMSG_STANDARD, "Unable to determine the user interface level the MSI is being run with, error code = '%lu'.", result);
delete [] wszValue;
return false;
}
if (0 == wcscmp(L"2", wszValue)) // INSTALLUILEVEL_NONE == 2
{
delete [] wszValue;
return true;
}
delete [] wszValue;
return false;
}
I believe I can work around this for now by passing the 'UILevel' property through WiX and checking for it that way in the C++, but I am curious what the problem here is as well.
I'm using Visual Studio/Visual C++ 2010 on Windows 7 with WiX 3.5.2519.
Thanks for any assistance you can provide!

Answer 1

Another way of making this simpler is to use the MsiEvaluateCondition function.
BOOL bUI = MsiEvaluateCondition(L"UILevel<3");
in C# using Microsoft.Deployment.WindowsIntaller (DTF) it's:
var uiLevel = session["UILevel"];
In C++ there's a sample at MsiGetProperty function:
UINT __stdcall MyCustomAction(MSIHANDLE hInstall)
{
TCHAR* szValueBuf = NULL;
DWORD cchValueBuf = 0;
UINT uiStat = MsiGetProperty(hInstall, TEXT("MyProperty"), TEXT(""), &cchValueBuf);
//cchValueBuf now contains the size of the property's string, without null termination
if (ERROR_MORE_DATA == uiStat)
{
++cchValueBuf; // add 1 for null termination
szValueBuf = new TCHAR[cchValueBuf];
if (szValueBuf)
{
uiStat = MsiGetProperty(hInstall, TEXT("MyProperty"), szValueBuf, &cchValueBuf);
}
}
if (ERROR_SUCCESS != uiStat)
{
if (szValueBuf != NULL)
delete[] szValueBuf;
return ERROR_INSTALL_FAILURE;
}
// custom action uses MyProperty
// ...
delete[] szValueBuf;
return ERROR_SUCCESS;
}

Answer 2

Thanks to #DanielGehriger, we figured out that the problem isn't with the code, but with the scheduling for the custom action. The UILevel MSI property is simply not available when running a deferred custom action (I found that the code worked correctly for a custom action scheduled for firstsequence). I have worked around this limitation by explicitly passing it on custom action data using WiX:
<CustomAction Id="CustomAction.SetProperty" Property="CustomActionCall"
Value="UILEVEL=[UILevel];" />
and then checking for this in the C++ with WcaIsPropertySet and WcaGetProperty. Note that the character case of the property name between square brackets matters here.