Resolving Issues with VBA Classes Not Executing from Collections of Dynamically Created Form Objects

Discover how to effectively manage `VBA Classes` in your project by keeping references to collections and ensuring event handling works correctly.
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This video is based on the question https://stackoverflow.com/q/66872318/ asked by the user 'Sjoerd' ( https://stackoverflow.com/u/15150886/ ) and on the answer https://stackoverflow.com/a/66872732/ provided by the user 'ArcherBird' ( https://stackoverflow.com/u/6071871/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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Understanding the Issue: VBA Classes and Collections

When working with VBA (Visual Basic for Applications), specifically in scenarios where forms and controls are dynamically generated, you might encounter unexpected behavior—like event handlers not executing as intended. This can be particularly frustrating for those who are relatively new to programming with classes in VBA.

In this guide, we will explore a common problem: why VBA classes linked to a collection of dynamically created form objects might not execute their event code correctly. We will present a streamlined solution to ensure your events fire as expected, thereby optimizing your workflow and enhancing performance.

The Problem

The core of the problem arises when dynamically created form objects are added to a collection, and the associated event handlers do not work as anticipated unless a particular workaround is applied. This can occur when the collection that holds the object references goes out of scope, leading to the collection—and hence your event handlers—being destroyed.

Simplified Code Structure

In the provided code snippet, there are three main components: form control creation, the collection that holds the control handlers, and the class to manage the events. Let’s break down the provided code for clarity:

Control Creation

[[See Video to Reveal this Text or Code Snippet]]

Class Code

In your class caCntrlHndlr, you define how the controls will react when interacted with. Your class holds the event procedures:

[[See Video to Reveal this Text or Code Snippet]]

Each of the controls has corresponding event handlers to respond to user interaction.

The Key Solution: Keeping a Reference

The critical solution to the issue of events not firing lies in ensuring that the cEvents collection is not destroyed at the end of your method or scope. You need to define the collection at a broader scope so it remains active and retains all its contained objects.

How to Fix it:

Declare the Collection at a Module Level: Instead of creating the collection within a method, declare it as a private module-level variable so it persists after the method execution:

[[See Video to Reveal this Text or Code Snippet]]

Add Controls to the Collection: Continue to add your dynamically created control handlers to the collection as you did before.

By following this approach, you ensure that your cEvents collection remains intact while your code executes, allowing your events to function correctly.

Conclusion

Understanding how VBA classes and collections work together is crucial for effective event handling in dynamically generated forms. By keeping a reference to your cEvents collection outside of your methods, you can ensure that your event handlers remain active and respond as expected during execution.

If you're still facing challenges, consider revisiting your object handling and scope management. With practice, you'll gain confidence in using classes to elevate your VBA projects. Happy coding!

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