Question

Is there any way for the main form to be able to intercept events firing on a subcontrol on a user control?

I’ve got a custom user-control embedded in the main Form of my application. The control contains various subcontrols that manipulate data, which itself is displayed by other controls on the main form. What I’d like is if the main form could be somehow informed when the user changes subcontrols, so I could update the data and the corresponding display elsewhere.

Right now, I am cheating. I have a delegate hooked up to the focus-leaving event of the subcontrols. This delegate changes a property of the user-control I’m not using elsewhere (in this cause, CausesValidation). I then have a delegate defined on the main form for when the CausesValidation property of the user control changes, which then directs the app to update the data and display.

A problem arises because I also have a delegate set up for when focus leaves the user-control, because I need to validate the fields in the user-control before I can allow the user to do anything else. However, if the user is just switching between subcontrols, I don’t want to validate, because they might not be done editing.

Basically, I want the data to update when the user switches subcontrols OR leaves the user control, but not validate. When the user leaves the control, I want to update AND validate. Right now, leaving the user-control causes validation to fire twice.

Answer 1

The best practice would be to expose events on the UserControl that bubble the events up to the parent form. I have gone ahead and put together an example for you. Here is a description of what this example provides.

• UserControl1
• Create a UserControl with TextBox1
• Register a public event on the UserControl called ControlChanged
• Within the UserControl register an event handler for the TextBox1 TextChangedEvent
• Within the TextChangeEvent handler function I call the ControlChanged event to bubble to the parent form
• Form1
• Drop an instance of UserControl1 on the designer
• Register an event handler on UserControl1 for MouseLeave and for ControlChanged

Here is a screenshot illustrating that the ControlChanged event that I defined on the UserControl is available through the UX in Visual Studio on the parent Windows form.