void GroupBox_DragDrop (object sender, DragEventArgs e)
{
if (e.Data.GetDataPresent (DataFormats.FileDrop)) {
string [] filenames = (string []) e.Data.GetData (DataFormats.FileDrop);
if (filenames != null) {
foreach (string fileName in filenames)
_filesListBox.Items.Add ("Drop => " + fileName);
}
}
}