GUI.SetNullEventHandler | Part of GUI module |
Syntax | GUI.SetNullEventHandler (nullHandler : procedure x ())
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Description | Sets the new null event handler. The nullHandler parameter is the name of a procedure that is called every time GUI.ProcessEvent is called and there are no mouse button presses or keystrokes to be processed. This is used by programs that need to call subprograms often, but do not wish to interrupt the action of user widgets.
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Example | The following program has a Quit button. When no widgets are being processed, a clock in the corner is updated.
import GUI View.Set ("graphics:220;50") var oldTime : string := "" var button : int procedure NullHandler var newTime : string := Time.Date newTime := newTime (11 .. *) if newTime not= oldTime then Text.Locate (maxrow, maxcol 9) put newTime .. oldTime := newTime end if end NullHandler GUI.SetNullEventHandler (NullHandler) button := GUI.CreateButton (10, 5, 100, "Quit", GUI.Quit) loop exit when GUI.ProcessEvent end loop |
Status | Exported qualified. This means that you can only call the function by calling GUI.SetNullEventHandler, not by calling SetNullEventHandler.
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See also | GUI.ProcessEvent.
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