Use text system or totally custom text view?
Use text system or totally custom text view?
- Subject: Use text system or totally custom text view?
- From: R.Matthew Emerson <email@hidden>
- Date: Tue, 3 Jun 2008 23:49:18 -0400
I work on a Common Lisp system (<http://trac.clozure.com/openmcl/>).
The lisp has an Objective-C bridge, and there's a more-than-a-demo
Cocoa IDE for it, though it is pretty rough around the edges in places.
An important part of the IDE is the editor. We're currently using an
emacs-like editor called Hemlock. Hemlock is written in Common Lisp,
so an editor buffer is a rich lisp data structure.
A Hemlock buffer is represented as a linked list of lines. A line is
a lisp string. A lisp string is a vector of characters (represented
internally as UTF-32/UCS-4 code points). This is quite different from
the usual way Cocoa represents text.
Also, being an emacs-like editor, Hemlock runs user-definable commands
in response to key events.
Right now, we have an NSTextStorage subclass that wraps a Hemlock
buffer. However, we end up maintaining a "mirror"
NSMutableAttributedString instance containing the buffer text anyway,
and there's a bit of hair involved in keeping the two in sync.
On the input side of things, we subclass NSTextView and override
keyDown:. From what I've read, this is usually the wrong thing to do,
but we want to do our own key bindings and don't want the default key
bindings getting in the way. On the other hand, we still want to use
input management.
Hemlock also has its own notion of selection, which is disjoint from
NSTextView's. I think we'd really like users to run (user-defined)
commands in response to mouse events, too. (Custom selection behavior
in different editing modes, etc.)
So, I'm really looking for advice on whether it's reasonable to keep
trying to use the Cocoa text system to support text display and input,
or if it would be better to make the (nontrivial) effort to write a
totally custom text view in a case like this.
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