Question

I am having some trouble with my custom RichTextBox control.

The RichTextBox does not seem to have any concept of a “Lines” collection. But I need to manage the text by line.

Is there a way to get AND update a line of text in a RichTextBox?

The exact scenario I am going for is to look at each line in the RichTextBox and, if the line has more than 60 chars, insert a Environment.NewLine after the 60th char.

Update:
I have found that you can GET a line with this code:

richTextBox.Document.ContentStart.GetLineStartPosition(lineNumber); 

But I still have no way to UPDATE a line.

Answer 1

You simple need to iterate over the lines, check the length, if it’s longer than 60, add a new line character. Repeat for all the characters in the line, and return the result.

Below is an outline of the code

private void richTextBox1_KeyUp(object sender, KeyEventArgs e)
{
    TextPointer line = richTextBox1.CaretPosition.GetLineStartPosition(0);
    if (line.GetOffsetToPosition(richTextBox1.CaretPosition) > 60)
    {
        line.GetPositionAtOffset(60, LogicalDirection.Forward).InsertLineBreak();
    }
}

The above code is useful, if you are running the formatting once.