解决此流不支持查找操作[Exception type: NotSupportedException]

var myrequest = WebRequest.Create("http//www.example.com/xxxxx.jpg");  
using (WebResponse response = myrequest.GetResponse())  
{
    using (Stream responseStream = response.GetResponseStream())
    {
        using (var stream = new MemoryStream())
        {
            const int bufferLength = 1024;
            int actual;
            byte[] buffer = new byte[bufferLength];
            while ((actual = responseStream.Read(buffer, 0, bufferLength)) > 0)
            {
                stream.Write(buffer, 0, actual);
            }
            stream.Position = 0;
            //逻辑处理
        }
    }
}