public frmMain()
{
this. richTextBox1.DragDrop += new System.Windows.Forms.DragEventHandler(arg);
}
private void richTextBox1_DragEnter(object sender,
System.Windows.Forms.DragEventArgs e)
{
if (e.Data.GetDataPresent(DataFormats.Text))
e.Effect = DragDropEffects.Copy;
else
e.Effect = DragDropEffects.None;
}