How can I replace text in UITextView with NSUndoManager support?

I want to be able to replace some text in an UITextView programatically, so I wrote this method as an UITextView category:

- (void) replaceCharactersInRange:(NSRange)range withString:(NSString *)newText{

    self.scrollEnabled = NO;

    NSMutableString *textStorage = [self.text mutableCopy];
    [textStorage replaceCharactersInRange:range withString:newText];

    //replace text but undo manager is not working well
    [[self.undoManager prepareWithInvocationTarget:self] replaceCharactersInRange:NSMakeRange(range.location, newText.length) 
                                                                       withString:[textStorage substringWithRange:range]];
    NSLog(@"before replacing: canUndo:%d", [self.undoManager canUndo]); //prints YES
    self.text = textStorage; 
    NSLog(@"after replacing: canUndo:%d", [self.undoManager canUndo]); //prints NO
    if (![self.undoManager isUndoing])[self.undoManager setActionName:@"replace characters"];
    [textStorage release];

    //new range:
    range.location = range.location + newText.length;
    range.length = 0;
    self.selectedRange = range;

    self.scrollEnabled = YES;

}

It works but NSUndoManager stops working (it seems to be reset) just after doing self.text=textStorage I have found a private API: -insertText:(NSString *) that can do the job but who knows if Apple is going to approve my app if I use it. Is there any way to get text replaced in UITextView with NSUndoManager Support? Or maybe I am missing something here?

There is actually no reason for any hacks or custom categories to accomplish this. You can use the built in UITextInput Protocol method replaceRange:withText:. For inserting text you can simply do:

[textView replaceRange:textView.selectedTextRange withText:replacementText];

This works as of iOS 5.0. Undo works automatically and there are no weird scrolling issues.