streamreader 和 streamwriter 以及 string 与 memorystream 使用示例

经常用到，但老记不住，备忘一下

using (var ms = new MemoryStream())
            {
                var sw = new StreamWriter(ms);
                sw.WriteLine("Hello World");
                sw.Flush();
                ms.Position = 0;
                var sr = new StreamReader(ms);
                var myStr = sr.ReadToEnd();
                Console.WriteLine(myStr);
            }