'\"
'\" Copyright (c) 1997 Maorong Zou
'\" 
.TH EZ_AddWidgetCallBack 3 "" EZWGL "EZWGL Functions"
.BS
.SH NAME
EZ_AddWidgetCallBack, EZ_RemoveWidgetCallBack,
EZ_RemoveAllWidgetCallBacks  \- register/remove callbacks associated to a widget

.SH SYNOPSIS
.nf
.B #include <EZ.h>
.sp
.BI "void EZ_AddWidgetCallBack( EZ_Widget *" widget ",
.BI "     int " which ", EZ_CallBack " callback ", void *" clientdata ", int " location )
.BI "void EZ_AddWidgetCallBack00( EZ_Widget *" widget ",
.BI "     int " which ", EZ_CallBack " callback ", void *" clientdata ", int " location )
.BI "void EZ_RemoveWidgetCallBack( EZ_Widget *" widget ",
.BI "     int " which ", EZ_CallBack " callback ", void *"clientdata )
.BI "void EZ_RemoveWidgetCallBack00( EZ_Widget *" widget ",
.BI "     int " which ", EZ_CallBack " callback ", void *"clientdata )
.BI "void EZ_RemoveAllWidgetCallBacks( EZ_Widget *" widget ", int "which )
.BI "void EZ_RemoveAllWidgetCallBacks00( EZ_Widget *" widget ", int "which )

.SH ARGUMENTS
\fIwidget\fR  Specifies an EZ widget.
.sp
\fIcallback\fR  Specifies a callback.
.sp
\fIclientdata\fR  Specifies an clientdata to be passed to the
callback.
.sp
\fIwhich\fR  Specifies a callback list. 
.sp
\fIlocation\fR  Specifies when the callback is to be called
relative to other previousely registered callbacks.
.sp
.SH DESCRIPTION
.PP
An \fBcallback\fR is a procedure of the following prototype:
.sp
.nf
    void (* callback)(void *object, void *data)
.fi
.PP
\fBEZ_AddWidgetCallBack\fR registers a callback to a widget. 
There are three callback lists associated to a widget: an
\fBEZ_CALLBACK\fR list, an \fBEZ_MOTION_CALLBACK\fR list and
an \fBEZ_DESTROY_CALLBACK\fR list. Motion callbacks are invoked 
whenever the the selection item changes. Normal callbacks are called 
when a Button1 press occurs on the widget window or a selection
is made. Destroy callbacks are invoked at the time a widget is
destroyed. If \fIlocation\fR is 0, the callback will be put in front
of all previously registered callbacks. If \fIlocation\fR is
1, the callback will be inserted at the end of all
previousely registered callbacks.
.PP
For composite widget, \fBEZ_AddWidgetCallBack\fR 
registers the callback to the most appropriate inter widget. To
register a callback to a composite widget itself, use
\fBEZ_AddWidgetCallBack00\fR.
.PP
\fBEZ_RemoveWidgetCallBack\fR deletes a callback from the
specified callback list. The specified
callback will be deleted only if both the procedure and
the client data match.
.PP
For composite widget, \fBEZ_RemoveWidgetCallBack\fR 
removes the callback from the most appropriate inter widget. To
remove a callback from a composite widget's callback list, use
\fBEZ_RemoveWidgetCallBack00\fR.
.PP
\fBEZ_RemoveAllCallBacks\fR deletes all callbacks from
the specified callback list.
.PP

.SH "SEE ALSO"
EZ_AddEventHandler(3)
.br