Mailing Lists: Apple Mailing Lists
Image of Mac OS face in stamp
 
[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

Re: understanding NSTextView undo?

On Saturday, December 28, 2002, at 12:30 PM, Jim Correia wrote:

I'm trying to understand the undo mechanism in NSTextView.

There doesn't seem to be much documentation about the mechanics. If I've overlooked something important in the docs, can someone point me at it?

Nope. It isn't documented. My comments are based on reverse engineering what NSTextView does in order to do similar coalescing on my own.

Question 1:

It seems that undo of typing is coalesced. This presents a problem for document applications because if you type, save, type, undo, it goes back to past the save point. Is there a way to force the coalescing to stop and start a new "group"? (This sounds like it should be a known bug, but unless someone confirms that it is, I'll file a bug..)

Whenever you type the text system uses private methods on NSUndoManager to examine the last undo invocation. If the last invocation is a typing change on this text view (and you haven't changed the selection or something in the meanwhile), then instead of adding a new undo invocation, it simply does nothing - the existing topmost undo will then undo back to when you first began typing.

So a couple possible ways to keep the text system from doing this is to:
1) Add your own undo invocation to the stack when you save (which doesn't need to do anything). Then when you next make a typing change, the text system looks at the top of the stack, sees it isn't a typing change, and makes a new undo group. You could also use this "on save" undo invocation call something that brings up a "you are about to go back before this file was saved" warning dialog.

2) You could also do something when you save to simply convince the text view that it should make a new typing "group". Probably the easiest way is to simply change the selection (to anything different), then change it back. NSTextView starts a new typing group if you change the selection between typing characters.

Question 2:

How do I make transformations in NSTextView undoable? The docs just say "This method must be invoked at the start of any sequence of user-initiated editing changes...." but don't say that it handles the undo for you. Poking around in the debugger, it appears that it does (and further, if it returns yes, and I do not subsequently replace the text, it puts the text view in an inconsistent state.)

So, is making an action undoable as simple as

[textView shouldChangeTextInRange: range replacementString: string];
// do replacement
[textView didChangeText];

It seems to be that simple, but I want to make sure I'm not missing something important here.

Yep. It's that simple.

Also, without providing my own implementation of shouldChangeTextInRange:replacementString: is it possible to affect the range that will be selected on redo?

Imagine that a transform inserts

[macroStart] macroText [marcoEnd]

and leaves macroText selected so that the user can type a replacement string.

But if I undo, then redo, the insertion point is left at the end of the inserted text. It would be nice if the selection range were preserved.

Yes, that would be nice.

I guess I would approach this by using your own controller object with -insertMacro: and -deleteMacro: methods, and have them register each other to undo each other's actions. You can set the selection range appropriately in each instead of depending upon NSTextView's undo management.

Hope this helps,
-Greg _______________________________________________
cocoa-dev mailing list | email@hidden
Help/Unsubscribe/Archives: http://www.lists.apple.com/mailman/listinfo/cocoa-dev
Do not post admin requests to the list. They will be ignored.
References: 
 >understanding NSTextView undo? (From: Jim Correia <email@hidden>)



Visit the Apple Store online or at retail locations.
1-800-MY-APPLE

Contact Apple | Terms of Use | Privacy Policy

Copyright © 2007 Apple Inc. All rights reserved.