[wix-users] Pass install directory to function in DLL for use at end of uninstall

[Michael Urman]

If you debug, I bet you'll see you sill receive ERROR_MORE_DATA from your
second call to MsiGetProperty. So reviewing the documentation of
*pchValueBuf* more closely, you are required to pass in a value that
represents space for a trailing null character, but the output value from
MsiGetProperty never includes this. So your vector length of (size + 1) is
good, but that also needs to be the value of size in your second call.

On Sun, May 29, 2016 at 12:01 AM, Lewie Fitz <lewfitz at gmail.com> wrote:

> Hello,
>
> I am trying to pass the install directory to a custom action function in
> my DLL written in C++, but I can't get it to work.
>
> The calling of the function works properly. Every time I execute the
> uninstall, I get a messagebox at the end. The problem is, I only ever get
> the error messagebox.
>
> To pass the install directory to the DLL function, I am using the method
> suggested by several articles online and by MSDN itself for deferred
> execution of a custom action. I am trying to set the install dir string to
> a property named after my deferred custom action.
>
> The following is the important bits of what I have done:
>
> WIX file
>
>         <Directory Id="TARGETDIR" Name="SourceDir">
>             <Directory Id="PublicDir">
>                 <Directory Id="APPLICATIONROOTDIRECTORY" Name="AppName"/>
>             </Directory>
>         </Directory>
>
>         <Binary Id="CustomUninstall"
> SourceFile="SourceFiles\CustomUninstall.dll"/>
>         <CustomAction Id="SetCustomActionData" Return="check"
> Property="CustomUninstall" Value="[APPLICATIONROOTDIRECTORY]"/>
>         <CustomAction Id="CustomUninstall" BinaryKey="CustomUninstall"
> DllEntry="_DLLFunction at 4" Execute="deferred" Impersonate="no"
> Return="ignore"/>
>
>         <InstallExecuteSequence>
>             <Custom Action="SetCustomActionData" After="CostFinalize"/>
>             <Custom Action="CustomUninstall"
> Before="InstallFinalize">Installed AND NOT UPGRADINGPRODUCTCODE</Custom>
>         </InstallExecuteSequence>
>
>
> CPP File
>
> extern "C" __declspec(dllexport) UINT __stdcall DLLFunction(MSIHANDLE
> session)
> {
>     DWORD size = 0;
>
>     UINT result = MsiGetProperty(session, L"CustomActionData,", L"",
> &size);
>     //size now contains the size of the property's string, without null
> termination
>
>     std::vector<WCHAR> buffer(size + 1);
>
>     if (result == ERROR_MORE_DATA)
>     {
>         result = MsiGetProperty(session, L"CustomActionData,",
> buffer.data(), &size);
>     }
>
>     if (result != ERROR_SUCCESS)
>     {
>         MessageBox(NULL, L"Error", L"", MB_OK);
>     }
>     else
>     {
>         std::wstring dir(buffer.data());
>         MessageBox(NULL, dir.c_str(), L"", MB_OK);
>     }
>
>     return ERROR_SUCCESS;
> }
>
>
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