< Grid  x:Name ="LayoutRoot"  Background ="AliceBlue" >

     < Grid.RowDefinitions >

         < RowDefinition  Height ="250" />

         < RowDefinition  Height ="25" />

         < RowDefinition  Height ="25" />

     </ Grid.RowDefinitions >

     < TextBox  Name ="Msg"  Grid.Row ="0"  Text ="请输入内容"  Width ="400"  Height ="200"  FontSize ="16"   />

     < Button  Name ="SaveFile"  Content =" 保  存 "  Grid.Row ="1"  Click ="SaveFileClick"  FontSize ="14"  Width ="200" />

     < TextBlock  Name ="FileName"   Grid.Row ="2"  FontSize ="14" />

</ Grid >

private   void  SaveFileClick( object  sender, RoutedEventArgs e)

{

    SaveFileDialog sfd  =   new  SaveFileDialog()

    {

        DefaultExt  =   " txt " ,

        Filter  =   " Text files (*.txt)|*.txt|All files (*.*)|*.* " ,

        FilterIndex  =   2

    };

     if  (sfd.ShowDialog()  ==   true )

    {

        FileName.Text  =   " 文件名称： "   +  sfd.File.Name;

         using  (Stream stream  =  sfd.OpenFile())

        {

            Byte[] fileContent  =  System.Text.UTF8Encoding.UTF8.GetBytes(Msg.Text);

            stream.Write(fileContent,  0 , fileContent.Length);

            stream.Close();

        }                

    }

}