C#中SaveFileDialog 和OpenFileDialog 的用法

private void btnOpen_Click(object sender, EventArgs e)
     {
         OpenFileDialog ofd = new OpenFileDialog();
         ofd.InitialDirectory = @"C:\Users\LWP1398\Desktop"; //设置初始路径
         ofd.Filter = "Excel文件(*.xls)|*.xls|Csv文件(*.csv)|*.csv|所有文件(*.*)|*.*"; //设置“另存为文件类型”或“文件类型”框中出现的选择内容
         ofd.FilterIndex = 2; //设置默认显示文件类型为Csv文件(*.csv)|*.csv
         ofd.Title = "打开文件"; //获取或设置文件对话框标题
         ofd.RestoreDirectory = true;
         if (ofd.ShowDialog() == DialogResult.OK)
         {
             //FileName：所选文件的全路径  SafeFileName：所选的文件名
             txtPath.Text = "FileName:" + ofd.FileName + "\r\n" + "SafeFileName:" + ofd.SafeFileName;
         }
     }

private void button3_Click(object sender, EventArgs e)
     {
         OpenFileDialog ofd = new OpenFileDialog();
         ofd.InitialDirectory = @"C:\Users\LWP1398\Desktop"; //设置初始路径
         ofd.Filter = "Excel文件(*.xls)|*.xls|Csv文件(*.csv)|*.csv|所有文件(*.*)|*.*"; //设置“另存为文件类型”或“文件类型”框中出现的选择内容
         ofd.FilterIndex = 2; //设置默认显示文件类型为Csv文件(*.csv)|*.csv
         ofd.Title = "打开文件"; //获取或设置文件对话框标题
         ofd.RestoreDirectory = true;////设置对话框是否记忆上次打开的目录

         ofd.Multiselect = true;//设置多选
         if (ofd.ShowDialog() == DialogResult.OK)
         {
             for (int i = 0; i < ofd.FileNames.Length; i++)
             {
                 txtPath.Text += ofd.FileNames[i] + "\r\n";//输出一个路径回车换行
             }
             for (int i = 0; i < ofd.FileNames.Length; i++)
             {
                 txtPath.Text += ofd.SafeFileNames[i] + "\r\n";
             }
         }
     }

private void button2_Click(object sender, EventArgs e)
     {
         SaveFileDialog sfd=new SaveFileDialog();
         sfd.Filter = "文本文件(*.txt)|*.txt|所有文件|*.*";//设置文件类型
         sfd.FileName = "保存";//设置默认文件名
         sfd.DefaultExt = "txt";//设置默认格式（可以不设）
         sfd.AddExtension = true;//设置自动在文件名中添加扩展名
         if (sfd.ShowDialog()==DialogResult.OK)
         {
             txtPath.Text = "FileName:" + sfd.FileName + "\r\n" ;
             using (StreamWriter sw = new StreamWriter(sfd.FileName))
             {              
                 sw.WriteLineAsync("今天是个好天气");
             }
         }
         MessageBox.Show("ok");
     }