On May 13, 2010, at 21:20, Richard Somers wrote: > Consider a Core Data document based application that uses a > NSArrayController. When the selected objects are removed or deleted and then > the user does an undo the selected objects are restored but the selection is > not. I have a custom view object. > > I would like the state of the selection to also be restored with an undo > similar to what happens when working with the Cocoa text system. When text is > selected, then deleted, and then the user does an undo, the restored text is > selected. > > Should I try to use the persistent document undo manager, create an undo > manager in the custom NSArrayController subclass, create an undo manager in > the custom view, or create an undo manager in one of my other classes?
This is a little bit harder than it seems. You certainly want to have the document undo manager keep track of the selection changes, in order to stay in sync with the really undoable changes. So: 1. You need to add a transient property for the selection to your managed data model. (Or non-transient, if you want the selection to persist when the document is re-opened.) 2. You need to keep track of the changes to the selection by modifying your Core Data selection property whenever the selection changes. However, you don't want these to be recorded as undoable actions (most likely, although there are scenarios -- think of Photoshop -- where selection changes are undoable), so you have to disable the undo manager temporarily around such changes. (Don't forget to invoke processPendingChanges before disabling the undo manager, and again before enabling it.) 3. You can't just track the selection state at the time of the undoable action, because the selection you ultimately want is different depending on whether you're undoing or redoing. (Convincing yourself that this is an issue is left as an exercise for the reader.) I think the easiest way to do this is to create an undo group for each action that needs to restore the selection, with 2 actions in the group: the first one changes all the non-selection properties to their new values; the second changes the selection property to the post-change selection. (The latter changes the selection without disabling the undo manager, of course.) I *think* that gives the right selection depending whether you're undoing or redoing. (But I haven't actually tried this approach. The last time I had to deal with this problem in a Core Data environment, I think I did something clunkier.) _______________________________________________ Cocoa-dev mailing list ([email protected]) Please do not post admin requests or moderator comments to the list. Contact the moderators at cocoa-dev-admins(at)lists.apple.com Help/Unsubscribe/Update your Subscription: http://lists.apple.com/mailman/options/cocoa-dev/archive%40mail-archive.com This email sent to [email protected]
