如何在Windows Installer上下文外调用其自定义动作DLL文件？

Absolutely, you can call these Windows Installer custom action DLLs outside of an actual MSI installation—you just need to simulate the Windows Installer session context that the DLL expects, especially for the MsiGetProperty calls that pull data from the installer.

Key Background First #

Most custom action DLLs export functions with a standard Windows Installer signature:

__declspec(dllexport) UINT __stdcall YourCustomActionName(MSIHANDLE hInstall);

The hInstall parameter is a handle to the MSI installation session, which MsiGetProperty relies on to fetch property values. To use the DLL externally, you need to provide a valid session handle and populate the required properties.

Method 1: Use Windows Installer APIs to Create a Temporary Session #

The most reliable approach is to leverage official Windows Installer APIs to create a valid session, set your required properties, then call the DLL's custom action function. Here's how:

Step-by-Step Breakdown #

1. Open an MSI Package
   Use MsiOpenPackage or MsiOpenProduct to get a valid MSIHANDLE. You can use any MSI (even a blank/test MSI if you don't need to interact with a real installer's state).
2. Set Required Properties
   Use MsiSetProperty to populate the properties your DLL's function expects via MsiGetProperty.
3. Load the DLL and Call the Function
   Use standard Windows API calls (LoadLibrary, GetProcAddress) to load the DLL and invoke the custom action function, passing the session handle you created.
4. Clean Up Resources
   Always close the session handle with MsiCloseHandle and free the DLL with FreeLibrary to avoid memory leaks.

Example Code (C++) #

#include <windows.h>
#include <msi.h>
#include <msiquery.h>
#pragma comment(lib, "msi.lib")

// Define the function pointer type for the custom action
typedef UINT(__stdcall* CustomActionFunc)(MSIHANDLE);

int main() {
    MSIHANDLE hInstall = NULL;
    // Open a test MSI (replace with your path)
    UINT openResult = MsiOpenPackage(L"C:\\Path\\To\\Test.msi", &hInstall);
    if (openResult != ERROR_SUCCESS) {
        MessageBox(NULL, L"Failed to open MSI package", L"Error", MB_ICONERROR);
        return 1;
    }

    // Set the property your DLL needs (replace with your property name/value)
    MsiSetProperty(hInstall, L"YOUR_TARGET_PROPERTY", L"YourDesiredValue");

    // Load the custom action DLL
    HMODULE hDll = LoadLibrary(L"C:\\Path\\To\\YourCustomAction.dll");
    if (hDll == NULL) {
        MessageBox(NULL, L"Failed to load DLL", L"Error", MB_ICONERROR);
        MsiCloseHandle(hInstall);
        return 1;
    }

    // Get the address of the custom action function
    CustomActionFunc pCustomAction = (CustomActionFunc)GetProcAddress(hDll, "YourCustomActionName");
    if (pCustomAction == NULL) {
        MessageBox(NULL, L"Failed to find custom action function", L"Error", MB_ICONERROR);
        FreeLibrary(hDll);
        MsiCloseHandle(hInstall);
        return 1;
    }

    // Call the custom action function
    UINT actionResult = pCustomAction(hInstall);

    // Cleanup
    FreeLibrary(hDll);
    MsiCloseHandle(hInstall);

    return actionResult;
}

Method 2: Hook MsiGetProperty (Advanced) #

If you don't want to rely on an MSI package, you can hook the MsiGetProperty function to intercept calls from the DLL and return your predefined values. This is more complex but useful for debugging or scenarios where you can't use an MSI.

How It Works #

• Use a hooking library (like Microsoft Detours) or manual hook techniques to redirect the DLL's calls to MsiGetProperty to your own function.
• In your hooked function, check the property name being requested and return the value you've preconfigured.

⚠️ Note: This approach is error-prone and can interfere with other Windows Installer operations running on the system. It's best reserved for testing/debugging rather than production use.

Critical Things to Keep in Mind #

• Permissions: Custom actions often run with elevated privileges during installation. Ensure your external caller has the same level of permissions (e.g., run as administrator) to avoid access denied errors.
• DLL Dependencies: The custom action DLL may depend on other Windows Installer APIs or system libraries. Make sure these are available in your runtime environment.
• Side Effects: Some custom actions modify system state (e.g., write to registry, create files). Test in an isolated environment to avoid unintended changes.
• Debugging: Use MsiEnableLog to enable MSI logging if you need to troubleshoot property values or function execution issues.

内容的提问来源于stack exchange，提问作者user1056903