winform 打开文件对话框关闭不了,该怎么解决

winform 打开文件对话框关闭不了
我建了一个项目，打开文件打开对话框，但是点取消后会重新跳一次文件打开对话框。再点一次取消才会关闭。是什么原因
public String OpenMinu()
  {
  string s = "";
  OpenFileDialog ofd = new OpenFileDialog();
  ofd.Title = "open";
  ofd.InitialDirectory = Environment.GetFolderPath(Environment.SpecialFolder.MyDocuments);
  ofd.Filter = "Text Document(*.txt)|*.txt|All Files|*.*";
  ofd.ValidateNames = true;
  ofd.CheckPathExists = true;
  ofd.CheckFileExists = true;
  ofd.Multiselect = false;
  if (ofd.ShowDialog() == DialogResult.OK)
  {
  try
  {
  string Filename = ofd.FileName;
  StreamReader sr = new StreamReader(Filename, Encoding.Default);
  s = sr.ReadToEnd().ToString();
  if (s == null)
  {
  s = Filename + ";";
  }
  else
  {
  s = Filename + ";" + s;
  }
  sr.Close();
  }
  catch (Exception)
  {
  }
  }
  else if (ofd.ShowDialog() == DialogResult.Cancel)
  {
  s = ";";
   
  }  
  return s;
  }
具体是什么原因？求指导

[解决办法]
if (ofd.ShowDialog() == DialogResult.OK) //打开一次
{。。。
}else if (ofd.ShowDialog() == DialogResult.Cancel)//打开第2次
{
。。。
}
[解决办法]

C# code

        private void button1_Click(object sender, EventArgs e)        {            DialogResult ret;            ret = ofd.ShowDialog();            if (ret == DialogResult.OK) //打开一次            {                ;            }            else if (ret == DialogResult.Cancel)//打开第2次            {                ;            }        }