c# xml序列化 FileStream

XmlSerializer serializer = new XmlSerializer(typeof(TextBox_Input));
FileStream fs = null;
try
{
fs = new FileStream("myxml.xml", FileMode.Create, FileAccess.ReadWrite);
// String fileName = "D:\C#\XmlCe\XmlCe\myxml.xml";
TextWriter writer = new StreamWriter(fs,Encoding.UTF8);
// StringWriter writers = new StringWriter(myxml);
serializer.Serialize(writer, textstring);
writer.Dispose();
}
finally
{
if (fs != null)
fs.Dispose();
}
错误：

                    msdn:有例子
                     private void SerializeCollection(string filename){
    Employees Emps = new Employees();
    // Note that only the collection is serialized -- not the 
    // CollectionName or any other public property of the class.
    Emps.CollectionName = "Employees";
    Employee John100 = new Employee("John", "100xxx");
    Emps.Add(John100);
    XmlSerializer x = new XmlSerializer(typeof(Employees));
    TextWriter writer = new StreamWriter(filename);
    x.Serialize(writer, Emps);

            但是我用了，StreamWriter(filename);vs不接受参数 string类型，接受streaml类型，很困惑，求大神帮忙解答。

http://blog.csdn.net/wyzxk888/article/details/6341009