private void Form1_DragEnter(object sender, DragEventArgs e)
        {
            // 當滑鼠拖曳進視窗，改變鼠標
            if (e.Data.GetDataPresent(DataFormats.FileDrop)) e.Effect = DragDropEffects.Copy;
        }

        private void Form1_DragDrop(object sender, DragEventArgs e)
        {
            // 當拖曳進來檔案放開滑鼠按鍵時，呼叫本函式
            string[] files = (string[])e.Data.GetData(DataFormats.FileDrop);
            foreach (string file in files) Console.WriteLine(file);
        }