Drag And Drop for WinForms

First set 'Allow Drop' to True

Next, add events for  

// Only allow drop if the item is a Directory

private void textBoxPath_DragOver(object sender, DragEventArgs e)

{

    string[] files = (string[])e.Data.GetData(DataFormats.FileDrop);

    if (files != null && files.Length > 0 && Directory.Exists(files[0]))

        e.Effect = DragDropEffects.Copy;

    else

        e.Effect = DragDropEffects.None;

}

private void textBoxPath_DragDrop(object sender, DragEventArgs e)

{

    string[] files = (string[])e.Data.GetData(DataFormats.FileDrop);

    if (files != null && files.Length > 0 && Directory.Exists(files[0]))

        textBoxPath.Text = files[0];

}