how to drag and drop from datagridview to richtextbox in C#?

As title, I want to drag 1 cell from datagridview to richtextbox ? I tried with my code but it doesn't work. I set rtb_ArticleTemplate.AllowDrop = true in constructor and I set EnableAutoDragDrop of richtextbox is true

private void rtb_ArticleTemplate_DragEnter(object sender, DragEventArgs e)
{
    string tt = e.Data.GetData(DataFormats.Text).ToString();
    if (e.Data.GetDataPresent(DataFormats.Text))

        e.Effect = DragDropEffects.Copy;
    else
        e.Effect = DragDropEffects.None;
}



private void rtb_ArticleTemplate_DragDrop(object sender, DragEventArgs e)
{
    int i;
    String s;

    // Get start position to drop the text.
    i = rtb_ArticleTemplate.SelectionStart;
    s = rtb_ArticleTemplate.Text.Substring(i);
    rtb_ArticleTemplate.Text = rtb_ArticleTemplate.Text.Substring(0, i);

    // Drop the text on to the RichTextBox.
    rtb_ArticleTemplate.Text = rtb_ArticleTemplate.Text + e.Data.GetData(DataFormats.Text).ToString();
    rtb_ArticleTemplate.Text = rtb_ArticleTemplate.Text + s;
}



private void dgv_Xpath_MouseDown(object sender, MouseEventArgs e)
{
    if (e.Button == MouseButtons.Left)
    {
        DataGridView.HitTestInfo info = dgv_Xpath.HitTest(e.X, e.Y);
        if (info.RowIndex >= 0)
        {
            if (info.RowIndex >= 0 && info.ColumnIndex >= 0)
            {
                string text = (string)
                       dgv_Xpath.Rows[info.RowIndex].Cells[info.ColumnIndex].Value;
                if (text != null)
                    dgv_Xpath.DoDragDrop(text, DragDropEffects.Copy);
            }
        }
    }
}