Not a 'New' Concept : Event Handler Methods in Dynamics 365 F&O

Remember the old days of having the ability to simply override the AX Form methods (i.e. Init, Lookup etc). It was fairly quick and easy way to do Form Customization. Well, this won’t be the case anymore as New Dynamics 365 F&O stops this ability to do in above manner. But please note it doesn’t mean these kinds of Customization is not available. Microsoft simply enforce us to do this kind of Customization in a different manner using Event Handler.

·      As we may know already this approach supports Microsoft’s strategy to write your Customized Code in Extensions (No More Over-layering / In-Line Code).

Also, please note that the Event Handler Option is not a brand-new concept and in fact it existed in Previous version (AX 2012). The difference is it was there as option before but now it is mandatory for such Customization.

Creating an Extension Class for Forms Code

To create an extension class for forms code, we can create a class which ends in _Extension. We only need to have the ExtensionOf decoration and ensure the name ends in _Extension.

Example of Class declaration:

[ExtensionOf(formStr(FormName))]final class MyFormName_Extension{}

-       With extension classes we can add member variables, and these variables will be associated with the form.

-       These variables can be referenced from any instance method. That way the state of the form can be maintained across different instance methods.

-       Extension classes instantiate automatically; there is no access to private methods, but we can add state variables and access them along with forms public variables and methods.

The event handlers can be created as an instance methods. There are two types of event handler: a pre-event and post-event handler.

-       Events are raised as preceding and succeeding operations around the base methods. We can write code to execute a before-base method (Pre-Event) or an after-base (Post-Event) method.

·         Copy event handler method: This option copies a method signature to the clipboard. You can paste it in any X++ code editor to define a method that subscribes to the selected event.

Get FormRun from form control

[FormControlEventHandler(formControlStr(MyForm, MyButton), FormControlEventType::Clicked)] public static void MyButton_OnClicked(FormControl sender, FormControlEventArgs e)
{
FormRun formRun = sender.formRun() as FormRun;
formRun.myCustomMethod();
}

Please Note: The event handler methods can be applied to Table level methods (i.e ValidateWrite) same way. Instead of overriding the methods, you would subscribe to Event Handler Method(s).