PRB: Loading and Unloading DLLs in the Design Environment

• Standard, Professional, and Enterprise Editions of Microsoft Visual Basic, 16-bit and 32-bit, for Windows, version 4.0

SYMPTOMS

You may not be able to overwrite a dynamic-link library (DLL) after calling into it from Visual Basic in design time while the Visual Basic design environment is still running. This problem is generally encountered when users are developing DLLs for Visual Basic and are debugging their DLL code.

CAUSE

When a function within a DLL is called by a program in the design environment, the DLL is loaded into memory. When the program is stopped, the DLL is kept in memory and is only unloaded when the user exits the design environment or when a hard edit is performed on a Declare statement that references the DLL. This prevents Visual Basic from having to load and unload DLLs every time the user runs and stops the program at design time.

RESOLUTION

You can force Visual Basic to unload a DLL by performing a hard edit on the Declare statement of a function that is declared within the DLL. For example, you can do a hard edit on the Declare statement by just deleting the "r" in "Declare" and then typing it back in. This forces a recompile, which causes Visual Basic to unload the DLL.