Intercepting undo while editing a cell-based table view

Question

I'd like to intercept or disable Cmd-Z/Shift-Cmd-Z during a text editing session for a table view cell.

It's a cell-based table view with a series of columns whose values affect each other, such that filling in some columns will populate others automatically. When the user presses Cmd-Z in the middle of an editing session, the undo manager can change the property currently being edited, with confusing results for the user.

Here's an example:

Step 1: User types ".030" in second column:

Step 2: User presses tab, model automatically updates columns three, four, and five:

Step 3: User presses Ctrl-Z, model undoes changes to columns two, three, four, and five, but editing session is still in progress, so old value shows in column three:

Step 4: Without typing anything, user presses tab which cancels editing, and value from column three disappears:

Nothing actually "wrong" is happening here, but it's confusing.

When one of the cells is being edited, I just want to intercept Cmd-Z and Shift-Cmd-Z and ignore them. I think I should be overriding -keyDown: in whatever is first responder during that editing. But what is that? The table view doesn't get those key events at all, and the cell isn't a responder either.

Answer 1

Found a working solution. In my NSTableView subclass:

// Disable undo and redo while table's field editors have first responder status
-(BOOL)validateMenuItem:(NSMenuItem *)menuItem {
    if (self != self.window.firstResponder)
        if (@selector(undo:) == menuItem.action || @selector(redo:) == menuItem.action)
            return NO;
    return YES;
}

// Intercept undo events while table's field editors have first responder status
-(IBAction)undo:(id)sender {
    if (self != self.window.firstResponder)
        [self noResponderFor:_cmd];
    else
        [self.nextResponder tryToPerform:@selector(undo:) with:sender];
}