OpenEdge Development:<br />Progress 4GL Reference VALID-HANDLE function

An expression that evaluates to a value of type HANDLE or WIDGET-HANDLE. If the handle represents an object that is currently valid, VALID-HANDLE returns TRUE. If the handle is no longer valid (if, for example, some procedure deleted the object), the function returns FALSE.

In the following example, the user creates a window dynamically. The WINDOW-CLOSE trigger uses the VALID-HANDLE function to determine whether the window has been created.

VALID-HANDLE ( `handle` )

r-valhnd.p
DEFINE VARIABLE mywin AS WIDGET-HANDLE. DEFINE BUTTON mkwin LABEL "New Window". ENABLE mkwin. ON CHOOSE OF mkwin DO: CREATE WINDOW mywin ASSIGN VISIBLE = TRUE TITLE = "Second Window" MAX-WIDTH-CHARS = 40 MAX-HEIGHT-CHARS = 10. SELF:SENSITIVE = FALSE. END. ON WINDOW-CLOSE OF DEFAULT-WINDOW DO: IF VALID-HANDLE(mywin) THEN DELETE WIDGET mywin. END. WAIT-FOR WINDOW-CLOSE OF DEFAULT-WINDOW.

r-valhnd.p

DEFINE VARIABLE mywin AS WIDGET-HANDLE.
DEFINE BUTTON mkwin   LABEL "New Window".

ENABLE mkwin.

ON CHOOSE OF mkwin
   DO:
      CREATE WINDOW mywin
          ASSIGN VISIBLE = TRUE
                 TITLE = "Second Window"
                 MAX-WIDTH-CHARS = 40
                 MAX-HEIGHT-CHARS = 10.
     SELF:SENSITIVE = FALSE.
   END.

ON WINDOW-CLOSE OF DEFAULT-WINDOW
   DO:
      IF VALID-HANDLE(mywin)
      THEN DELETE WIDGET mywin.
   END.
   
WAIT-FOR WINDOW-CLOSE OF DEFAULT-WINDOW.

In the example, the VALID-HANDLE function returns a TRUE value only if the window has been created (that is, mywin does not have the Unknown value (?)) and the window has not been deleted. Therefore, the DELETE WIDGET statement executes only if mywin is a valid widget handle.

Notes

A widget handle becomes invalid if the associated widget or procedure is deleted or is out of scope.

This function is useful when walking through a list of widgets or persistent procedures using the PREV-SIBLING or NEXT-SIBLING attributes.

VALID-HANDLE(handle:PREV-SIBLING) is FALSE when you reach the first handle in the list. VALID-HANDLE(handle:NEXT-SIBLING) is FALSE when you reach the last handle in the list.

The VALID-HANDLE function supports handles to AppServers, proxy persistent procedures, remote persistent procedures, and COM objects. For more information on AppServers, see OpenEdge Application Server: Developing AppServer Applications . For more information on COM objects, see OpenEdge Development: Programming Interfaces .

VALID-HANDLE function

Syntax

Notes

See also