KILLING callback

Typically assigned in the Constructor by:

!this.KillingCall = '!this.<form_method>'

The purpose is to notify the form that it is being destroyed and allow the assigned callback method to destroy any associated resources, for example, Global PML objects which would otherwise not be destroyed. This may be necessary because PML Global objects will survive an application module switch, but may not be valid in the new module.

Note:
The callback method must not carry out any modifications to the Gadgets belonging to the form or to the Form itself (for example, do not show or hide the form). Attempts to edit the form or its gadgets may cause unwanted side effects or possible system errors.

Note:
Form callbacks designed for other Form events (CANCEL, INIT) are rarely suitable as killing callbacks.
Restrict form and gadget operations to querying.