How do I set a property to the last typed symbol in richtextbox in wpf?

Question

I want to set some background or foreground properties to the latest symbol in RichTextBox.

I tried getting the latest textrange by saving the caret position before the input and then getting the textrange like that: new TextRange(previousCaret, currentCaret).

However this is a bug-prone decision, because you can actually get 2 or more last symbols in case if the caret position wasn't updated in time (for example, you are typing very quickly and pressing the buttons at the same time)

Now, maybe I don't even have to get the latest symbol's TextRange? Are there other ways, like some built-in methods?

So, how do I change the latest symbol's properties properly?

Answer 1

To get the latest TextRange, simply use this code:

private TextRange LatestSymbol
{
    get
    {
        var previous = InputString.CaretPosition.GetPositionAtOffset(-1);

        if (previous != null)
        {    
             return new TextRange(
                      previous,
                      InputString.CaretPosition
                    );
                }
            return null;
        }
    }
}

The thing here is, that CaretPosition.GetPositionAtOffset(-1) returns the position that is 1 symbol behind the currentPosition.

And this works well and without any bugs.