读取/写入xml变量

Question

I have been looking for a while how to write a list of details of each player registered on a server so that when people log in, their details are loaded from the xml file and they resume from where they logged off.

I know there are a lot of tutorials out there, but I cant seem to make any work. I need random access and for the file to be updated on the hard disk in real time. Current code (far from working) shows the sort of format im after, but I dont understand most concepts of xml, for example what is an attribute/node/element? tutorials seem to like to assume you know..

XMLFile = XDocument.Load(@"C:/users.xml");
var users = XMLFile.Descendants( "Users" );
int count = 0;
foreach ( var user in users )
{
  count++;
  userName[count] = user.ToString();

  XElement element = (XMLFile.FirstNode as XElement);
  userPass[count] = element.Value;

  XAttribute attribute = (XMLFile.NextNode as XAttribute);
  userLocation[count] = attribute.Value;

  attribute = (XAttribute)XMLFile.NextNode;
  userRotation[count] = attribute.Value;
}

The idea is that the file would be formatted something like this (as xml..)

Users
    Aaron
        password
        vector3 of location
        Quaternion of Rotation
    SomeoneElse
        hispassword
        Vector3 of location
        Quaternion of rotation
    //and so on....

The values would be read upon a client logging in and sent accross the network everything else works I just cant get any method of reading/writing xml to work so thanks for the help.

Answer 1

First of all it's not a valid XML format. I guess you meant this:

<Users>
   <User>
    <Username>...</Username>
    <Password>...</Password>
    <Location>...</Location>
    <Rotation>..</Rotation>
  </User>

</Users>

Second, as i see you storing each user values into seperate arrays, why ? Just add a User class, and define a collection of Users, and for reading use this code:

XDocument xDoc = XDocument.Load(@"C:/users.xml");
List<User> users = (from u in xDoc.Descendants("User")
                    select new User {
                        Name = u.Element("Username").Value,
                        Password = u.Element("Password").Value,
                        Location = u.Element("Locations").Value,
                        Rotation = u.Element("Rotation").Value
                    }).ToList();

And you asked " what is an attribute/node/element "

Let's assume we have this element:

<User ID = "23">
   <Username>User123</Username>
</User>

In this particular element:

• ID is an Xml Attribute
• User and Username are Xml Element
• User is parent element of Username
• And everything is Xml Node , for Example: User is an Element Node , "User123" is a Text Node etc...

Update: Write to XML

If you have this xml structure you can simply append new values like this (or create a new xml):

I assume you have a collection named users

XElement xmlElement = new XElement("Users",
            from user in users
            select new XElement("User",
                new XElement("Username", user.Username),
                new XElement("Password", user.Password),
                new XElement("Location", user.Location),
                new XElement("Rotation", user.Rotation)));
xmlElement.Save("Users.xml");

Update: Validate User

string userName = textBox1.Text;
string password = textBox2.Text;
XDocument xDoc = XDocument.Load(@"C:/users.xml");
var userControl = (from u in xDoc.Descendants("User") 
                    where u.Element("Username").Value == userName
                         && u.Element("Password").Value == password
                           select u).Any();

if(userControl)
{
    // validated...
} else {
 // User doesn't exist or password wrong
}

Answer 2

First of all you can consider these two xml document formats:

This one is using attributes to store your data:

<Users>
  <User UserName="User1" Pass="Pass1" Location="Location1" Rotation="Rotaition1" />
  <User UserName="User2" Pass="Pass2" Location="Location2" Rotation="Rotaition2" />
</Users>

and this one is using elements to store your data:

<Users>
  <User>
    <UserName>User1</UserName>
    <Pass>Pass1</Pass>
    <Location>Location1</Location>
    <Rotation>Rotation1</Rotation>
  </User>
  <User>
    <UserName>User2</UserName>
    <Pass>Pass2</Pass>
    <Location>Location2</Location>
    <Rotation>Rotation2</Rotation>
  </User>
</Users>

Sample code for creating first structure:

    XDocument xDocument = new XDocument();
    XElement rootElement = new XElement("Users");
    rootElement.Add(new XElement("User", new XAttribute("UserName", "User1"), new XAttribute("Pass", "Pass1"), new XAttribute("Location", "Location1"), new XAttribute("Rotation", "Rotaition1")));
    rootElement.Add(new XElement("User", new XAttribute("UserName", "User2"), new XAttribute("Pass", "Pass2"), new XAttribute("Location", "Location2"), new XAttribute("Rotation", "Rotaition2")));
    xDocument.Add(rootElement);

Sample code for reading first structure:

var xElement = xDocument.Descendants("User").Single(element => element.Attribute("UserName").Value == "User1");

Sample code for creating second structure:

    XDocument xDocument = new XDocument();
    XElement rootElement = new XElement("Users");

    XElement userElement = new XElement("User");
    userElement.Add(new XElement("UserName", "User1"));
    userElement.Add(new XElement("Pass", "Pass1"));
    userElement.Add(new XElement("Location", "Location1"));
    userElement.Add(new XElement("Rotation", "Rotation1"));
    rootElement.Add(userElement);

    userElement = new XElement("User");
    userElement.Add(new XElement("UserName", "User2"));
    userElement.Add(new XElement("Pass", "Pass2"));
    userElement.Add(new XElement("Location", "Location2"));
    userElement.Add(new XElement("Rotation", "Rotation2"));
    rootElement.Add(userElement);

    xDocument.Add(rootElement);

And finally, sample code for reading second structure:

var xElement = xDocument.Descendants("User").Single(element => element.Element("UserName").Value == "User1");

You cas save and load you xml document using this sample:

xDocument.Save("Your xml file path"); // using Save() instance method
XDocument xDocument = XDocument.Load("Your xml file path"); // using Load() static method

Its your decision whether to choose first structure or second based on your requirements, ease of usage and best practices for a well formed xml document. In this case I prefer the first structure. For further reading about a well formed xml document refer to this codeproject article: Well-Formed XML

Note that, the above codes are just some samples for creating those two kinds of xml documents. In your case you just have to iterate through users collection and create the xml elements in your loop based on each user object.

You also asked about xml basic concepts. The previous answer by @Selman22 is quick and correct, but for further info see these references:

1. http://www.w3schools.com/xml/default.asp
2. http://msdn.microsoft.com/en-us/library/bb387019.aspx

Answer 3

Just serialize your user array (or user object and use multiple files) to XML using the XML serializer. http://msdn.microsoft.com/en-us/library/182eeyhh(v=vs.110).aspx

Write an file (from MSDN)

MySerializableClass myObject = new MySerializableClass();
// Insert code to set properties and fields of the object.
XmlSerializer mySerializer = new 
XmlSerializer(typeof(MySerializableClass));
// To write to a file, create a StreamWriter object.
using (StreamWriter myWriter = new StreamWriter("myFileName.xml"))
{   
   mySerializer.Serialize(myWriter, myObject);
}

Read from an object (from MSDN)

MySerializableClass myObject;
// Construct an instance of the XmlSerializer with the type
// of object that is being deserialized.
XmlSerializer mySerializer = 
new XmlSerializer(typeof(MySerializableClass));
// To read the file, create a FileStream.
using (FileStream myFileStream = new FileStream("myFileName.xml", FileMode.Open))
{
   // Call the Deserialize method and cast to the object type.
   myObject = (MySerializableClass) 
   mySerializer.Deserialize(myFileStream)
}

As an aside, writing to disk in "real time" is very expensive, and you may want to consider limiting your disc accesses. If your users have a "save" option, you could do your disc write then, or do it on some kind of timer.

As far as random access is concerned, that should be done in memory (not in the file). Basically your flow would be: User logs in -> Read user data from file into memory -> User does stuff -> update object in memory -> user saves or "autosave" -> write object to disk.