FileStream文件读写?

Question

// 将多个dc.graphicsList写入一个文件    
            foreach (DrawingCanvas dc in canvasList)
                {
                    SerializationHelper helper = new SerializationHelper(dc.graphicsList);
                    XmlSerializer xml = new XmlSerializer(typeof(SerializationHelper));                    using (Stream stream = new FileStream(FileName,
                    FileMode.Append, FileAccess.Write, FileShare.None))
                    {
                        xml.Serialize(stream, helper);
                        dc.ClearHistory();
                        dc.UpdateState();
                    }
                }怎么从这个文件中分别把各个dc.graphicsList读取出来?
实在没分了, 就剩这么多了..

Answer 1

读取的时候
                SerializationHelper helper;                XmlSerializer xml = new XmlSerializer(typeof(SerializationHelper));                using (Stream stream = new FileStream(FileName,
                    FileMode.Open, FileAccess.Read, FileShare.Read))
                {
// 这一句有异常
                    helper = (SerializationHelper)xml.Deserialize(stream);
                }

Answer 2

因为项目关系,有些东西要用c#做, 我也才开始胡乱看了点c#的代码,写出来的东西肯定
不怎么样,序列化什么的不大懂, 就请将就下看看我代码哪里有问题了. 
不过我也不觉得我的代码很复杂啊.. 可能我是搞vc的吧, 逻辑思维一下转不过来