Modification of RichTextBox

[Jolied]

Can part of the text already in RichTextBox, for example, change the colour of the text for this part of the text?

[zymir]

Sure. You only need one. https://msdn.microsoft.com/en-us/library/system.windows.documents.textpointer(v=vs.110).aspx to the right position of the text.

Name TextPointer At the beginning of the text, let's share the symbols from the second to the fourth:

var range = new TextRange(start.GetPositionAtOffset(2), start.GetPositionAtOffset(4));
range.ApplyPropertyValue(TextElement.ForegroundProperty, Brushes.Green);
range.ApplyPropertyValue(TextElement.BackgroundProperty, Brushes.Yellow);

The question is how to get the beginning of the text. Here's the code:

RichTextBox rtb = ...;
FlowDocument doc = rtb.Document;
TextPointer start = doc.ContentStart;

I'm not quite sure, because doc.ContentStart starting point FlowDocumentYeah, he's coming. ParagraphAnd then the text. That's why it's better to do this:

while (start != null &&
       start.GetPointerContext(LogicalDirection.Forward) != TextPointerContext.Text)
    start = start.GetNextContextPosition(LogicalDirection.Forward);
if (start == null)

// в документе нет текста, выходим