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Language Reference


VALID-HANDLE Function

Interfaces
OS
SpeedScript
All
All
No

Verifies that a handle is valid.

SYNTAX

VALID-HANDLE ( handle ) 

handle

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 If the handle is no longer valid (if, for example, some procedure deleted the object), the function returns FALSE.

EXAMPLE

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.

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

SEE ALSO

CREATE SERVER Statement, WIDGET-HANDLE Function


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