//選擇文件路徑
 private void btnPath_Click(object sender, EventArgs e)
 {
     OpenFileDialog ofd = new OpenFileDialog();
     if (ofd.ShowDialog() == DialogResult.OK)
     {
         textBox1.Text = ofd.FileName;
     }
 }
 //調用文件轉base64
 private void btnBase64_Click(object sender, EventArgs e)
 {
     textBox2.Text = FileToBase64String(textBox1.Text);
     MessageBox.Show("成功");
 }
 //調用base64轉文件
 private void btnFile_Click(object sender, EventArgs e)
 {
     SaveFileDialog sfd = new SaveFileDialog();
     sfd.Filter = "文件|*" + textBox1.Text.Substring(textBox1.Text.LastIndexOf('.'));
     if (sfd.ShowDialog() == DialogResult.OK)
     {
         Base64StringToFile(textBox2.Text, sfd.FileName);
         MessageBox.Show("成功");
     }
 }
 
 //文件轉base64
 public string FileToBase64String(string path)
 {
     try
     {
         string data = "";
         using (MemoryStream msReader = new MemoryStream())
         {
             using (FileStream fs = new FileStream(path, FileMode.Open))
             {
                 byte[] buffer = new byte[1024];
                 int readLen = 0;
                 while ((readLen = fs.Read(buffer, 0, buffer.Length)) > 0)
                 {
                     msReader.Write(buffer, 0, readLen);
                 }
 
             }
             data = Convert.ToBase64String(msReader.ToArray());
         }
 
         return data;
     }
     catch (Exception ex)
     {
         throw ex;
     }
 
 }
 
 //base64轉文件
 public void Base64StringToFile(string base64String, string path)
 {
     try
     {
         using (MemoryStream stream = new MemoryStream(Convert.FromBase64String(base64String)))
         {
             using (FileStream fs = new FileStream(path, FileMode.OpenOrCreate, FileAccess.Write))
             {
                 byte[] b = stream.ToArray();
                 fs.Write(b, 0, b.Length);
             }
         }
     }
     catch (Exception ex)
     {
         throw ex;
     }
 }