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Re: Correct implementation of undoManagerForTextView

On 4 Mar 2004, at 3:33 am, Dustin Voss wrote:

Secondly, there is an NSWindow delegate method that supplies an undo manager. If a text view needs an undo manager, it follows the responder chain, and will get one of these (in order):
* One returned by the NSTextView delegate's -undoManagerForTextView:

That's the one I want. The documentation tells me that "If you want a text view to have its own NSUndoManager (and not the windows), have the text views delegate implement undoManagerForTextView:, to return the NSUndoManager." What it doesn't tell me is how to implement this method. What do I return?

Well, I don't know why you don't want to use the window's and drawer's default undo manager, but given that you don't...

This is the setup. I have TextView A in the main window. This view is always present. I then have TextView B in the drawer, which is sometimes present. When either view loads new content from file or closes, I need to check that there are no unsaved changes. If insaved changes are found, then a dialog is put up asking the user if they want to save. So far so standard. However, let's say the user edits view A, then opens the drawer to check something in view B, then closes the drawer (without having edited it). As the drawer closes, the application looks for unsaved changes in view B. When it looks, it finds that there are undos registered (but has no way of knowing that these changes are in the main window, not the drawer). It puts up an Unsaved Changes dialog and the user goes "Huh? I didn't edit anything."

Just have the delegate objects instantiate an NSUndoController in the -init method, and return it.

I assume you mean NSUndoManager. (I got all excited when I read that - I thought I'd overlooked a whole undo-related controller class.) I tried putting undoManager = [[NSUndoManager alloc] init]; in the -init method of each delegate and returning,

- (NSUndoManager *)undoManagerForTextView:(NSTextView *)aTextView
{
return undoManager;
}

This made the entire undo system go haywire - e.g. hitting Undo removed the entire contents of the view, undos failed to register, or they registered but didn't enable the Undo menu item. As far as I could tell, I now had three undo managers (or three conflicting pointers to the same undo manager) - one for each delegate, plus the default manager for the main window, which was still trying to manage everything.

As an alternative, I set -undoManagerForTextView: to return [[myTextView window] undoManager] in each delegate. This should have given me two managers - one for the window, one for the drawer - but in fact it put me right back where I started - i.e. editing View A, then querying -canUndo for View B returned YES.

I feel like I'm being unbelievably obtuse about this.
-Jeremy

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References: 
 >Correct implementation of undoManagerForTextView (From: Jeremy Dronfield <email@hidden>)
 >Re: Correct implementation of undoManagerForTextView (From: Dustin Voss <email@hidden>)
 >Re: Correct implementation of undoManagerForTextView (From: Jeremy Dronfield <email@hidden>)
 >Re: Correct implementation of undoManagerForTextView (From: Dustin Voss <email@hidden>)



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