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Re: Correct implementation of undoManagerForTextView

On 3 Mar 2004, at 9:08 pm, Dustin Voss wrote:

On 3 Mar, 2004, at 10:32 AM, Jeremy Dronfield wrote:

My app has two separate text views (one in the main window, another in a drawer). Each has its own separate delegate, and I want each to have its own undo manager. (So that they can separately trigger an Unsaved Changes warning.) The trouble is, I can't figure out the correct implementation of the NSTextView delegate method:

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

There's no illumination in the FM, and I'm further confused by a reference by Bill Cheeseman (Omni archives) to this as an NSWindow delegate method, which it clearly isn't.

Firstly, the undo manager is not in charge of unsaved changes warnings. Your model should keep track of this itself.

That's what I meant. The undo manager isn't in charge - it's consulted.

NSDocument keeps track by observing the NSUndoManager it maintains, and other parts of the framework check with NSDocument to see if there are unsaved changes.

I'm not using NSDocument. Each text view has a delegate (an NSObject subclass).


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?

Thirdly, depending on how your app is laid out, are you sure you want two undo managers? Remember that the undo manager controls the undo stack. Let's say the user makes a change A in the first text view, change B in the second, and change C in the first. With two undo managers, he will be be able to undo C then A when he is in the first text view, but if he switches to the second, he will only be able to undo B.

That's the behaviour I want. The main window is always present, whereas the drawer opens and closes, so tracking changes and saving is handled separately for each text view. Furthermore, if the user is editing text view A and hits undo, it would be disastrous if the result was to undo something typed a few minutes before in text view B.

-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>)



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