private void textBox1_DragDrop(object sender, DragEventArgs e)
        {
            if (e.Data.GetDataPresent(DataFormats.FileDrop))
            {
                string[] rs = (string[])e.Data.GetData(DataFormats.FileDrop);
                MessageBox.Show(rs[0]);
            } 
        }
    
        
        private void Form1_DragEnter_1(object sender, DragEventArgs e)
        {
            //只允许文件拖放
            if (e.Data.GetDataPresent(DataFormats.FileDrop))
            {
                e.Effect = DragDropEffects.Copy;
            }
            else
            {
                e.Effect = DragDropEffects.None;
            }
        }