RitchTextBox で論理行
GetLineFromCharIndex は WordWrap してると使い物になんねえ!
private void richTextBox1_DoubleClick(object sender, EventArgs e) { var l = 0; var t = richTextBox1.Text; for (var i = 0; i < richTextBox1.SelectionStart; i++) if (t[i] == '\n') l++; }