void TabControl_Drop(object sender, DragEventArgs e) { var files = (string[])e.Data.GetData(DataFormats.FileDrop); if (files.Length > 0) { var move = Keyboard.Modifiers == ModifierKeys.Shift; var process = move ? "Move" : "Copy"; var confirmBox = new ConfirmBox($"{process} file", $"Move already existing cards\nto the current category (if any)?"); var reorganize = confirmBox.ShowDialog().Value; foreach (var file in files) { SelectedTab.AddImageFromOutside(file, move, reorganize); } } }