Subclassing NSTextView makes undo impossible in Cocoa

Question

I have a very simple Cocoa program. One window, with an NSTextView inside of it. In this configuration, the NSTextView operates exactly how you would expect it to. I can type, undo, redo, everything.

But then I subclass NSTextView, lets call it TextView. This new class does not override any methods, it's basically a blank subclass. I replace the NSTextView with my new subclass of it. I can type text into the TextView, but undo does not work. It just beeps at me. The undo menu item is greyed out. I would not expect this to happen, since TextView doesn't add any new code to the object inheritance structure.

What must I do to my TextView to re-enable undo?

GitHub project

XIB object hierarchy, "Text View" is my "TextView" class

Edit: upon further observation, there indeed was an edit in my subclass that caused the issue, as Mohamad Farhand opined.

Exactly how did you "replace the NSTextView with my new subclass of it"? Did you remove the object and add a new one or did you just change the class of the text view in the Identity inspector? — Ken Thomases
I just tried this and it works for me. When you replaced the text view, are you sure you didn't replace the scroll views? I can't see why it didn't work for you. Perhaps host a version of this non-working code on GitHub. — rein
Hi Rein, I added a GitHub project, please see above. Just run, enter characters into the text view, and try to undo. — Henry Rillovian

1024jp 1024jp · Accepted Answer · 2016-10-25T17:34:46

You may need to enable allowsUndo property of your subclassed TextView class.

@implementation TextView

- (nullable instancetype)initWithCoder:(nonnull NSCoder *)coder
{
    self = [super initWithCoder:coder];
    if (self) {
        self.allowsUndo = YES;
    }
    return self;
}

@end

Subclassing NSTextView makes undo impossible in Cocoa

2 Answers