Override of Event Handlers

You can override an event handler with or without calling the base method.

To override an event handler without invocation of the base method, use code based on the following template.

protected virtual _(Events.[EventName]<[DACName], [FieldName]> e) 
{
  … 
}

To override an event handler with invocation of the base method, use code based on the following template.

protected virtual void _(
    Events.[EventName]<[DACName], [FieldName]> e, 
    PX[EventName] baseMethod)
{
  baseMethod(e.Cache, e.Args);
  … 
}

For example, to override an event handler for the RowSelected event of the CurrencyInfo class, use the following code.

protected virtual void _(Events.RowSelected<CurrencyInfo> e, PXRowSelected baseMethod)
{
  baseMethod(e.Cache, e.Args);
}

Overriding Event Handlers with Delegate Parameters That Have the Generic Delegate Signature

The MYOB Acumatica Framework’s event handler override mechanism supports only event handlers whose delegate parameters' signature matches the signature of a graph’s classic event handler (shown below).

protected virtual void _(Events.FieldUpdating<APInvoice, APInvoice.docBal> e, 
  PXFieldUpdating fieldUpdatingBase)
{
}

Here, the second parameter has a classic delegate type: PXFieldUpdating.

The mechanism doesn't support overrides whose delegate parameters' signature matches the signature of a graph’s generic event handler, such as Action<Events.FieldUpdating<…>> in the following example.

protected virtual void _(Events.FieldUpdating<APInvoice, APInvoice.docBal> e,
    Action<Events.FieldUpdating<APInvoice, APInvoice.docBal>> fieldUpdatingBase)
{
}

Note that it's not the exact delegate type that matters—that is, whether it’s PXFieldUpdating, PXFieldUpdated, or your own custom delegate. What matters is the delegate's signature, specifically:

• The return type
• The list of parameter types
• The list (if any) of generic type parameters

If your delegate parameters' signature matches the signature of a graph’s classic event handler, the system will detect the override and wire it up correctly. Thus, the system recognizes the following override even though it doesn’t use the PXFieldUpdating delegate type.

protected virtual void _(Events.FieldUpdating<APInvoice, APInvoice.docBal> e,
    Action<PXCache, PXFieldUpdatingEventArgs> fieldUpdatingBase)
{
}

Internally, PXFieldUpdating, PXFieldUpdated, and all other predefined delegate types are just delegate aliases that are available for your convenience. The override mechanism doesn’t treat those aliases specially.