| Microsoft Office 2000/Visual Basic Programmer's Guide | |
Before you can call a function in a DLL from VBA, you must provide VBA with information about where that function is and how to call it. There are two ways to do this: by setting a reference to the DLL's type library, or by using a Declare statement in a module.
Setting a reference to a DLL's type library is the easiest way to work with functions in the DLL. Once you set the reference, you can call the DLL function as though it were part of your project. There are a couple of caveats, however. First of all, setting references to multiple type libraries can affect your application's performance. Secondly, not all DLLs provide type libraries. Although you can set a reference to a DLL that doesn't provide a type library, you can't call functions in that DLL as though they were part of your project.
Note that the DLLs that form the Windows API don't provide type libraries, so you can't set references to them and call their functions. To call a function in the Windows API, you must include a Declare statement in the Declarations section of a module in your project.
A Declare statement is a definition that tells VBA where to find a particular DLL function and how to call it. The easiest way to add a Declare statement to your code is to use the API Viewer add-in, which contains Declare statements for most of the functions in the Windows API, as well as the constants and type definitions that some functions require.