我试图简单地将 append 两种不同的数据类型放入我的 xml 文件并再次读取它们，但我收到错误

Question

I'm using Winforms and I get the following error when I press the load button after having hit the save button:

InvalidOperationException: was not expected.

Here is my code:

private void save_Click(object sender, EventArgs e)
{
    // if you don't specify it, then it saves in the bin folder of the program
    FileStream fs = new FileStream(@"C:\Users\Owner\Desktop\Student2.Xml", FileMode.Append, FileAccess.Write); //@"C:\Users\Owner\Desktop\Student.Xml"

    StudentClass sc = new StudentClass();

    sc.Name = textBox1.Text;
    sc.Class = int.Parse(textBox2.Text);

    ls.Add(sc);
       
    StudentSerializer.Serialize(fs, ls);
    DicSerializer.Serialize(fs,
                            dict.Select(kv => new DicItem() { id = kv.Key, value = kv.Value }).ToArray());

    fs.Close();
}

private void load_Click(object sender, EventArgs e)
{
    FileStream fs = new FileStream(@"C:\Users\Owner\Desktop\Student2.Xml", FileMode.Open, FileAccess.Read);

    ls = (List<StudentClass>)StudentSerializer.Deserialize(fs);

    var orgDict = ((DicItem[])DicSerializer.Deserialize(fs))
                     .ToDictionary(i => i.id, i => i.value);

    foreach (var item in orgDict) 
         Debug.WriteLine(item.Key + " and " + item.Value);

    fs.Close();
}

My dictionary already has two items in it. And my student class has two items as well from the textboxes. Also note, my xml file gets wiped clean after that error. Any help is appreciated thanks.

Also, this is what my xml looks like right after hitting the save button:

<?xml version="1.0"?>
<ArrayOfStudentClass xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xsd="http://www.w3.org/2001/XMLSchema">
  <StudentClass>
    <Name>wewewe</Name>
    <Class>2222</Class>
  </StudentClass>
</ArrayOfStudentClass><?xml version="1.0"?>
<DicItem xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xsd="http://www.w3.org/2001/XMLSchema">
  <DicItem id="1" value="one" />
  <DicItem id="2" value="two" />
</DicItem>

Answer 1

The complaint is because of <?xml version="1.0"?> right before the first DictItem tag. Such tag AFAIK should appear once only in the XML file.

You should post the Deserializer code for each class for more investigation.

Answer 2

If you remove the second declaration than following code will work

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Xml;
using System.Xml.Linq;

namespace ConsoleApplication1
{
    class Program
    {
        const string FILENAME = @"c:\temp\test.xml";
        static void Main(string[] args)
        {
            XmlReaderSettings settings = new XmlReaderSettings();
            settings.ConformanceLevel = ConformanceLevel.Fragment;

            XmlReader reader = XmlReader.Create(FILENAME, settings);

            reader.ReadToFollowing("ArrayOfStudentClass");
            XElement ArrayOfStudentClass = (XElement)XElement.ReadFrom(reader);

            reader.ReadToFollowing("DicItem");
            XElement DicItem = (XElement)XElement.ReadFrom(reader);

        }
    }
}