Silverlight独立存储空间的问题求大神

[huzhong_vip]

开发环境：Silverlight4
思路：一个Silverlight程序，功能是，有3个按钮，分别实现，在独立存储空间中创建XML，读取独立存储空间中XML，写入XML。
创建XML按钮代码：

private void button1_Click(object sender, RoutedEventArgs e)
        {
            try
            {
                XElement imgBox = new XElement("imgBox", new XElement("img", new XElement("source", "asdsad"), new XElement("width", "150"), new XElement("height", 150)));

                XDocument imgXml = new XDocument(new XDeclaration("1.0", "utf-8", "yes"), new XComment("这是一个XML文件"), imgBox);

                using (IsolatedStorageFile userFile = IsolatedStorageFile.GetUserStoreForApplication())
                {
                    using (IsolatedStorageFileStream fileStream = new IsolatedStorageFileStream("imgXml.xml", FileMode.Create, userFile))
                    {
                        imgXml.Save(fileStream);
                        fileStream.Close();
                        MessageBox.Show("chenggong");
                    }
                }
            }
            catch(IsolatedStorageException ex)
            {
                MessageBox.Show(ex.ToString());
            }

        }

读取XML按钮代码：

private void button3_Click(object sender, RoutedEventArgs e)
        {
            try
            {
                using (IsolatedStorageFile userfile = IsolatedStorageFile.GetUserStoreForApplication())
                {
                    using (IsolatedStorageFileStream filestream = userfile.OpenFile("imgXml.xml", FileMode.Open, FileAccess.Read))
                    {
                        StreamReader str = new StreamReader(filestream);
                        TextBox textbox = new TextBox();
                        textbox.Text = str.ReadToEnd().ToString();
                        textbox.Height = 350;
                        this.LayoutRoot.Children.Add(textbox);
                        str.Close();
                    }
                }
            }

写入XML按钮代码：

private void button4_Click(object sender, RoutedEventArgs e)
        {
            XDocument imgXml = null;
            try
            {
                using (IsolatedStorageFile file = IsolatedStorageFile.GetUserStoreForApplication())
                {

                        using (IsolatedStorageFileStream fileStream = new IsolatedStorageFileStream("imgXml.xml", FileMode.Open, file))
                        {
                            imgXml =XDocument.Load(fileStream);
                            
                            XElement new1 = new XElement("img", new XElement("source", "11111"), new XElement("width", "222"), new XElement("height", "555"));
                            
                            imgXml.Root.Add(new1);
                            imgXml.Save(fileStream);
                            fileStream.Close();
                            MessageBox.Show("添加成功");
                        }
                }
            }
            catch (IsolatedStorageException ex)
            {
                MessageBox.Show(ex.ToString());
            }
        }

问题：点击创建按钮后再点击读取XML按钮能正常创建和读取XML

<?xml version="1.0" encoding="utf-8" standalone="yes"?>
<!--这是一个XML文件-->
<imgBox>
  <img>
    <source>asdsad</source>
    <width>150</width>
    <height>150</height>
  </img>
</imgBox>

但是点击写入XML按钮后，XML就变成了这样，这是怎么回事，怎么解决？

<?xml version="1.0" encoding="utf-8" standalone="yes"?>
<!--这是一个XML文件-->
<imgBox>
  <img>
    <source>asdsad</source>
    <width>150</width>
    <height>150</height>
  </img>
</imgBox><?xml version="1.0" encoding="utf-8" standalone="yes"?>
<!--这是一个XML文件-->
<imgBox>
  <img>
    <source>asdsad</source>
    <width>150</width>
    <height>150</height>
  </img>
  <img>
    <source>11111</source>
    <width>222</width>
    <height>555</height>
  </img>
</imgBox>

我想要的效果是点击写入XML按钮后在XML文件中再添加元素，效果是这样的

<?xml version="1.0" encoding="utf-8" standalone="yes"?>
<!--这是一个XML文件-->
<imgBox>
  <img>
    <source>asdsad</source>
    <width>150</width>
    <height>150</height>
  </img>
  <img>
    <source>11111</source>
    <width>222</width>
    <height>555</height>
  </img>
</imgBox>

[huzhong_vip]

搞定了。。。不应该把imgXml.Save(fileStream);放到using (IsolatedStorageFileStream fileStream = new IsolatedStorageFileStream("imgXml.xml", FileMode.Open, file)) 中