removing RichTextBox lines while keeping the colour of remaining lines in C#

Question

Consider a RichTextBox which has 400 lines and includes a number of words and lines in diffident colours.

Is it possible to remove the first 100 lines of this text b

Answer 1

Use the SelectionText property. First select the lines you want to remove, then remove them by setting SelectionText to an empty string. Like this:

   richTextBox1.SelectionStart = 0;
   richTextBox1.SelectionLength = richTextBox1.GetFirstCharIndexFromLine(200);
   richTextBox1.SelectedText = "";

This preserves the formatting of all the other lines. This can cause visible flicker on the UI, you can suppress that by implementing the Begin/EndUpdate methods as shown here.