Windows Installer DLL Custom Actions

InstallShield 2019 Express Edition

If you need to perform an action in your installation that is not natively supported by InstallShield or the Windows Installer service, you can create a custom action that calls an entry-point function from a Windows Installer .dll file. With this type of custom action, often called an MSI DLL action, the function must be defined with the following signature:

UINT __stdcall FunctionName (MSIHANDLE hInstall) {...}

The function name can vary; however, the return type, calling convention, and single parameter must use the types that are specified in the aforementioned signature. The MSIHANDLE data type that is used in the function signature is a handle to the running installation.

The following sample code is for a function called MyFunctionName.

UINT __stdcall MyFunctionName (MSIHANDLE hInstall)

{

    MessageBox(

        GetForegroundWindow( ),

        TEXT("This is MyFunctionName."),

        TEXT("Custom Action"),

        MB_OK | MB_ICONINFORMATION);

    return ERROR_SUCCESS;

}

Your entry-point function should return ERROR_SUCCESS to indicate that the action finished successfully. If your custom action returns a non-zero value and you selected No for the custom action’s Ignore Exit Code setting, the installation exits. If you selected Yes for the custom action’s Ignore Exit Code setting, the installation continues, regardless of the custom action’s return code.

Once your MSI DLL is ready, you must design a custom action to call the entry-point function. To learn how to create the custom action, see Adding an MSI DLL Custom Action to Your Project.

Requirements

Both Msiquery.h and Msi.lib can be found in the Windows Installer SDK, which can be downloaded from Microsoft’s Web site. In addition to the two files listed above, the Windows Installer SDK contains Microsoft’s definitive documentation on the Windows Installer APIs.

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