private void Form_Main_DragDrop(object sender, DragEventArgs e)
        {
            string[] fileNames = (string[])e.Data.GetData(DataFormats.FileDrop, false);
            switch (currentMode)
            {
            case CurrentMode.Text:
                TextUtility.LoadTextToTextBox(textBox_Content, fileNames[0]);
                break;

            case CurrentMode.FileList:
                FileListUtility.AppendFileList(fileListItems, fileNames);
                break;
            }
        }