var fileContent = string.Empty;
var filePath = string.Empty;

using (OpenFileDialog openFileDialog = new OpenFileDialog())
{
    openFileDialog.InitialDirectory = "c:\\";
    openFileDialog.Filter = "txt files (*.txt)|*.txt|All files (*.*)|*.*";
    openFileDialog.FilterIndex = 2;
    openFileDialog.RestoreDirectory = true;

    if (openFileDialog.ShowDialog() == DialogResult.OK)
    {
        //Get the path of specified file
        filePath = openFileDialog.FileName;

        //Read the contents of the file into a stream
        var fileStream = openFileDialog.OpenFile();

        using (StreamReader reader = new StreamReader(fileStream))
        {
            fileContent = reader.ReadToEnd();
        }
    }
}

MessageBox.Show(fileContent, "File Content at path: " + filePath, MessageBoxButtons.OK);

//引入命名空间
using System;
using System.Windows.Forms;
using System.IO;

class MainClass
{

  public static void Main() 
  {
    OpenFileDialog dlgOpen = new OpenFileDialog();
    if (dlgOpen.ShowDialog() == DialogResult.OK)
    {
      string s = dlgOpen.FileName;
      Console.WriteLine("Filename " + s);
      Console.WriteLine(" Created at " + File.GetCreationTime(s));
      Console.WriteLine(" Accessed at " + File.GetLastAccessTime(s));
    }

  }

}