ITT Rule IDL Version 7.0 User Manual download pdf (Page 357)

Chapter 15: Creating a Custom iTool Widget Interface 357

iTool Developer’s Guide Handling Shutdown Events

Your code should not assume that the top-level base widget will actually be

destroyed, because the user may decide to cancel the close operation. Since the

process of actually destroying the widget hierarchy is divorced from the generation of

the WIDGET_KILL_REQUEST event, you may also need to supply a cleanup

routine that is invoked only when the widget hierarchy is actually destroyed.

Writing a Cleanup Routine

A cleanup routine is necessary if your widget interface uses heap variables (pointers

or objects) to store information about itself — the heap variables will need to be

cleaned up separately when the interface itself is destroyed. The following code, from

the cleanup routine in the

example2_wdtool.pro interface definition (developed

in “Example: a Custom iTool Interface” on page 360), frees the pointer used to store

the widget interface’s state structure.

PRO example2_wdtool_cleanup, wChild

; Make sure we have a valid widget ID.

IF (~WIDGET_INFO(wChild, /VALID)) THEN $

RETURN

; Retrieve the pointer to the state structure, and

; free it.

WIDGET_CONTROL, wChild, GET_UVALUE = pState

IF (PTR_VALID(pState)) THEN $

PTR_FREE, pState

END

Calling the Cleanup Routine

The final step is to specify when the cleanup routine should be called. Since the user

can cancel out of the shutdown operation, the cleanup routine should only be called

when the widget hierarchy is actually destroyed, not when the

WIDGET_KILL_REQUEST event is handled. We accomplish this by specifying the

cleanup routine as the value of the KILL_NOTIFY keyword to the WIDGET_BASE

function.

In the standard iTool widget interface and in our example code, we set the

KILL_NOTIFY keyword on the first child widget of the top-level base widget. The

following statement, near the end of the interface definition routine, specifies the

name of the cleanup routine in the

example2_wdtool.pro interface definition

(developed in “Example: a Custom iTool Interface” on page 360):

WIDGET_CONTROL, wChild, KILL_NOTIFY = "example2_wdtool_cleanup"

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ITT Rule IDL Version 7.0 User Manual Page 357