这是Winform直接封装好的打开文件对话框 

using System.Windows.Forms;
public static string OpenFile(string path)
{

      OpenFileDialog openFileDialog = new OpenFileDialog();
      // 设置对话框属性
      openFileDialog.Title = "选择文件";
      openFileDialog.InitialDirectory = path; // 设置初始目录
      openFileDialog.Filter = "TXT 文件|*.txt|所有文件|*.*"; //过滤器类型
      openFileDialog.FilterIndex = 1; // 默认选择第一个过滤器
      openFileDialog.RestoreDirectory = true; // 对话框关闭后恢复当前目录
      openFileDialog.CheckFileExists = false;  // 允许文件不存在
      openFileDialog.CheckPathExists = true;   // 但路径必须存在
      if (openFileDialog.ShowDialog() == DialogResult.OK)
       {
            return   openFileDialog.FileName;
       }
       return "";
}