OpenFileDialog ofd = new OpenFileDialog();
ofd.Filter = "Microsoft Office Excel(*.xls;*.xlsx)|*.xls;*.xlsx";
ofd.FilterIndex = 1;
ofd.RestoreDirectory = true;


if (ofd.ShowDialog() == DialogResult.OK)
{
   //检测打开文件路径是否为空地址
   if (!string.IsNullOrEmpty(ofd.FileName))
   {
          ReadFromExcelFile(ofd.FileName);
   }
   else
   {
          this.textBox1.Text = "请打开excel文件";
    }
} 

using(OpenFileDialog ofd = new OpenFileDialog()){　ofd.ShowDialog();　}

/// <summary>
    /// 单线程打开excel文档
    /// </summary>
    /// <param name="sender"></param>
    /// <param name="e"></param>
    private void btnXlx_Click(object sender, EventArgs e)
    {
      this.textBox1.Text = string.Empty;

      System.Threading.Thread s = new System.Threading.Thread(new System.Threading.ThreadStart(getExcel));
      s.ApartmentState = System.Threading.ApartmentState.STA;
      s.Start();

    }

    /// <summary>
    /// 读取excel文档地址
    /// </summary>
    private void getExcel()
    {
      OpenFileDialog ofd = new OpenFileDialog();
      ofd.Filter = "Microsoft Office Excel(*.xls;*.xlsx)|*.xls;*.xlsx";
      ofd.FilterIndex = 1;
      ofd.RestoreDirectory = true;


      if (ofd.ShowDialog() == DialogResult.OK)
      {
        //检测打开文件路径是否为空地址
        if (!string.IsNullOrEmpty(ofd.FileName))
        {
          ReadFromExcelFile(ofd.FileName);
        }
        else
        {
          this.textBox1.Text = "请打开excel文件";
        }
      }
    }