Winforms RichTextBox: How can I scroll the caret to the middle of the RichTextBox?

Question

I want to scroll a RichTextBox so that the caret is approximately in the middle of the RichTextBox.

Something like RichTextBox.ScrollToCaret(), except I don\'t want

Answer 1

If the rich text box is in _rtb, then you can get the number of visible lines:

public int NumberOfVisibleLines
{
    get
    {
        int topIndex = _rtb.GetCharIndexFromPosition(new System.Drawing.Point(1, 1));
        int bottomIndex = _rtb.GetCharIndexFromPosition(new System.Drawing.Point(1, _rtb.Height - 1)); 
        int topLine = _rtb.GetLineFromCharIndex(topIndex);
        int bottomLine = _rtb.GetLineFromCharIndex(bottomIndex);
        int n = bottomLine - topLine + 1;
        return n;
    }
}

Then, if you want to scroll the caret to, say, 1/3 of the way from the top of the richtextbox, do this:

int startLine = _rtb.GetLineFromCharIndex(ix);
int numVisibleLines = NumberOfVisibleLines;

// only scroll if the line to scroll-to, is larger than the 
// the number of lines that can be displayed at once.
if (startLine > numVisibleLines)
{
    int cix = _rtb.GetFirstCharIndexFromLine(startLine - numVisibleLines/3 +1);
    _rtb.Select(cix, cix+1);
    _rtb.ScrollToCaret();
}