'\"
'\" Copyright (c) 1997 Maorong Zou
'\" 
.TH EZ_AddItemCallBack 3 "" EZWGL "EZWGL Functions"
.BS
.SH NAME
EZ_AddItemCallBack,EZ_RemoveItemCallBack,
EZ_RemoveAllItemCallBacks  \- register/remove callbacks associated to
a display item

.SH SYNOPSIS
.nf
.B #include <EZ.h>
.sp
.BI "void EZ_AddItemCallBack( EZ_Item *" item ",
.BI "     int " which ", EZ_CallBack " callback ", void *" clientdata ", int " location )
.BI "void EZ_RemoveItemCallBack( EZ_Item *" item ",
.BI "     int " which ", EZ_CallBack " callback ", void *" clientdata )

.BI "void EZ_RemoveAllItemCallBacks( EZ_Item *" item ", int "which )

.SH ARGUMENTS
\fIitem\fR  Specifies a display item.
.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 previously 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_AddItemCallBack\fR registers a callback to a item. 
There are two callback lists associated to a item: an
\fBEZ_CALLBACK\fR list and an \fBEZ_DESTROY_CALLBACK\fR list.
Normal callbacks are called when a double Button1 click occurs on a
item.  Destroy callbacks are invoked at the time a item 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
\fBEZ_RemoveItemCallBack\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
\fBEZ_RemoveAllCallBacks\fR deletes all callbacks from
the specified callback list.

.SH "SEE ALSO"
EZ_CreateItem(3), EZ_ConfigureItem(3), EZ_SetItemClientData(3)