UITextView undo manager do not work with replacement attributed string (iOS 6) - uitextview

Question

iOS 6 has been updated to use UITextView for rich text editing (a UITextView now earns an attributedText property —which is stupidly non mutable—). Here is a question asked on iOS 6 Apple forum under NDA, that can be made public since iOS 6 is now public...
In a UITextView, I can undo any font change but cannot undo a replacement in a copy of the view's attributed string. When using this code...
- (void) replace: (NSAttributedString*) old with: (NSAttributedString*) new
{
1. [[myView.undoManager prepareWithInvocationTarget:self] replace:new with:old];
2. old=new;
}
... undoing is working well.
But if I add a line to get the result visible in my view, the undoManager do not fire the "replace:with:" method as it should...
- (void) replace: (NSAttributedString*) old with: (NSAttributedString*) new
{
1. [[myView.undoManager prepareWithInvocationTarget:self] replace:new with:old];
2. old=new;
3. myView.attributedText=[[NSAttributedString alloc] initWithAttributedString:old];
}
Any idea? I have the same problem with any of the replacement methods, using a range or not, for MutableAttributedString I tried to use on line "2"...

Answer 1

Umm, wow I really didn't expect this to work! I couldn't find a solution so I just started trying anything and everything...
- (void)applyAttributesToSelection:(NSDictionary*)attributes {
UITextView *textView = self.contentCell.textView;
NSRange selectedRange = textView.selectedRange;
UITextRange *selectedTextRange = textView.selectedTextRange;
NSAttributedString *selectedText = [textView.textStorage attributedSubstringFromRange:selectedRange];
[textView.undoManager beginUndoGrouping];
[textView replaceRange:selectedTextRange withText:selectedText.string];
[textView.textStorage addAttributes:attributes range:selectedRange];
[textView.undoManager endUndoGrouping];
[textView setTypingAttributes:attributes];
}

Answer 2

Mac Catalyst (iOS14)
UITextView has undoManager that will manage undo and redo for free without any additional code.
But replacing its attributedText will reset the undoManager (Updating text and its attributes in textStorage not work for me too). I found that undo and redo will works normally when formatting text without replacing attributedText but by standard edit actions (Right click on highlighting text > Font > Bold (Mac Catalyst)).
So to fix this :
You need to set the allowsEditingTextAttributes of UITextView to be true, this will make UITextView support undo and redo of attributedText.
self.textView.allowsEditingTextAttributes = true
If you want to change the text of attributedText, use replace(_:withText:) of UITextInput, or insertText(_:) and deleteBackward() of UIKeyInput that UITextView conforming to.
self.textView.replace(self.textView.selectedTextRange!, withText: "test")
If you want to change attributes of text, use updateTextAttributes(conversionHandler:) of UITextView instead.
self.textView.updateTextAttributes { _ in
let font = UIFont.boldSystemFont(ofSize: 17)
let attributes: [NSAttributedString.Key: Any] = [
.font: font,
]
return attributes
}
For changing text and its attributes in specific range, modify the selectedRange of UITextView.
To implement undo and redo buttons, check this answer : https://stackoverflow.com/a/50530040/8637708
I have tested with Mac Catalyst, it should work on iOS and iPadOS too.

Answer 3

The Undo Manager is reset after setting its 'text' or 'attributedText' property, this is why it does not work. Whether this behavior is a bug or by design I don't know.
However, you can use the UITextInput protocol method instead.
(void)replaceRange:(UITextRange *)range withText:(NSString *)text
This works.