From: Hidetoshi NAGAI <nagai@...>
Date: 2005-05-24T17:56:34+09:00
Subject: Re: Tk read-only text box

From: nornagon <nornagon@gmail.com>
Subject: Re: Tk read-only text box
Date: Tue, 24 May 2005 15:40:25 +0900
Message-ID: <14d61533050523234070e4f92a@mail.gmail.com>
> > For example,
> > ---------------------------------------------------
> > require 'tk'
> > t = TkText.new.pack
> > t.bindtags_unshift(b = TkBindTag.new)
> > b.bind('Key', proc{ Tk.callback_break })
> > 
> > t.insert(:end, "This is a test message.\n");
> > 
> > Tk.after(10000){t.insert(:end, "This is another test message.\n")}
> > 
> > Tk.mainloop
> > ---------------------------------------------------
> 
> Interesting. Could you tell me how that works, exactly? Like, what's
> bindtags_unshift do? What's a BindTag, even?

Each widget has a bindtag list to determine bindings which should be 
appleid. The default value of the list is [<self>, <class of the
widget>, <toplevel which the widget is placed on>, 'all'].
When an event occurs on the widget, one or none of the procedures 
binded to each bindtag is called. Of course, the event sequence of 
the binding  has to matche the event. Usually, the calling process is
done in order of the bindtag list. Tk.callback_break can break the
sequence and complete the operation for the event.

You can get/set the bindtag list by bindtags/bindtags= method. And can
add a new bindtag to the head of the list by bindtags_unshift method
(remove the head by bindtags_shift method). 

If you remove <class of the widget> from a bindtag list of a widget, 
the widget lose all bindings of the widget class. If add <class of the
widget> again, the widget gets the bindings of the widget class again.

Well, in the example case, a new bindtag is inserted at head of the 
bindtag list of the text widget. The bindtag has a binding for all
"Key" events. And the binding is "Tk.callback_break", that is, "finish
the operation for the event".

The operataion "insert a key-pressed character" is one of the bindings
for a kind of "Key" event. And it is binded on <class of the widget>,
that is, "TkText".

However, on the example, all kind of "Key" events are blocked on the
new bindtag and aren't checked on "TkText" tag. So, keyboard events
cannot change the text widget. 

# The reason of why don't remove "TkText" tag is to be able to accept 
# mouse events.
-- 
Hidetoshi NAGAI (nagai@ai.kyutech.ac.jp)