How to Trigger Events in Your Main Form from a Nested Child Form in C#

Learn how to effectively communicate between multiple forms in a C# application by triggering events from a nested child form back to the main form.
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This video is based on the question https://stackoverflow.com/q/69008983/ asked by the user 'valdrinNereth' ( https://stackoverflow.com/u/16625013/ ) and on the answer https://stackoverflow.com/a/69009312/ provided by the user 'valdrinNereth' ( https://stackoverflow.com/u/16625013/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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How to Trigger Events in Your Main Form from a Nested Child Form in C#

Developing applications with multiple forms in C# can sometimes lead to challenges, especially when trying to manage events across these forms. One common scenario arises when you need to trigger an action in your main form when a nested child form (or another form) is closed. This post will address a specific case of this issue — how to properly trigger an event on your main form when the child form's child form gets closed.

The Problem Summary

You have a main form that opens a search form via a button click. The search form can, in turn, open another form (the search results form). You want to trigger an event in your main form when the search results form closes, but your current approach isn’t working. Breakpoints indicate that the event handler for the form closure is not being triggered, leading to complications in your workflow.

Original Code Structure

In your original implementation, the core of the problem lies in how the forms are being instantiated. You created two separate instances of the frmSearchList form — one in the main form and another in the search form. Let’s take a closer look at the relevant part of your code:

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The issue arises because you are declaring a new instance of frmSearchList in both your main and search forms. Each instance operates independently, so closing one does not notify the other.

The Solution

To resolve this problem, you must ensure that the same instance of frmSearchList is used across both the main form and the search form. Here’s how to implement this fix step-by-step:

1. Declare a Global Instance

Create a single instance of frmSearchList that can be accessed by both the main form and the search form, which can be declared in your main form or in a globally accessible way.

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2. Modify the Main Form

Update your main form's event handler to use the single instance instead of creating a new one each time.

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

3. Update the Search Form

Ensure that the search form uses the global instance of frmSearchList.

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4. Final Adjustments

In the search results form, the closing action remains the same:

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

5. Test Your Changes

With these modifications finished, run your application again. When the frmSearchList is closed, the event in frmSearchTriggerEvent should now properly get triggered.

Conclusion

You've successfully set up your application to trigger an event in your main form from a nested child form. Ensuring that only one instance of the target form is used is crucial for inter-form communication in C# . By following the steps outlined above, you can avoid common pitfalls and ensure that your forms work harmoniously together. If you encounter any further issues, remember to check your form instances and event subscriptions.

With these guidelines, you can streamline interactions between multiple forms in your C# applications. Happy coding!

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