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Writing Add-ins Can Be Tricky

Writing Add-ins Can Be Tricky

Writing add-ins for Visual Basic 4.0 can be challenging, rewarding,and tricky. If you are not careful writing add-ins, you can causeVB to do strange things and even abort. Although I’m sure thatother diagnostics can occur, this error has appeared more thanonce for me while I was debugging add-ins. The messages may vary,depending on the operating system, but the result is the same.

For example, under Windows 95, you might see “This programhas caused an error and will be terminated?” or “Ifthe problem persists, contact the vendor.?” Under Windows3.1, it may result in a GPF.

These occur when the IDE is being unloaded and will be followedon a subsequent reload of VB with this: “xxxxxx add-in couldnot be loaded, do you want to remove it from the list of Add-ins?”

After this, you will have to re-execute the add-in to reregisterit for attachment to VB. I have found two causes for these errors:

1. Referencing a property of the VBIDE Instance Object, such asActiveProject.Filename in the ConnectAddin Event of the ConnectorClass.

2. Connecting more menu or sub-menu items than you disconnect.

Most programming is an exact science, and strict adherence to”mostly undocumented” rules is an absolute necessitywhen writing add-ins for VB4.

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