C# Serialization for xml

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C# Tutorial - XML Serialization

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// http://www.switchonthecode.com/tutorials/csharp-tutorial-xml-serialization
// # Tutorial - XML Serialization
// Posted in:
// 
//     * Tutorials
//     * .NET
//     * .NET 2.0
//     * C#
// 
// Related Posts
// 
//     * C# Tutorial - Method Attributes And Reflection
//     * C# Tutorial - Serialize Objects to a File
//     * Great Set of Video Tutorials on iPhone UITableView
//     * PHP Tutorial - Creating and Modifying SQLite Databases

// A long while ago we posted a tutorial on how to serialize objects to a binary file. 
// While this is very useful, unfortunately the resulting file is not very human readable. 
// In this tutorial, I'm going to demonstrate how to serialize your own objects to and from an XML file.

// Since .NET can use reflection to get property names, basic serialization is unbelievably simple. 
// It only gets slightly difficult when you want to name your XML tags differently than your property 
// names (but still not very hard). If you've ever used an XML serialization package in C++ like boost, 
// tinyXML, or libXML2, you'll see how comparatively easy C# is to use.

// Let's start with a basic example. Below is an object that stores some information about a movie.

public class Movie
{
  public string Title
  { get; set; }

  public int Rating
  { get; set; }

  public DateTime ReleaseDate
  { get; set; }
}

// All right, now that we have an object, let's write a function that will save it to XML.

static public void SerializeToXML(Movie movie)
{
  XmlSerializer serializer = new XmlSerializer(typeof(Movie));
  TextWriter textWriter = new StreamWriter(@"C:\movie.xml");
  serializer.Serialize(textWriter, movie);
  textWriter.Close();
}

// The first thing I do is create an XMLSerializer (located in the System.Xml.Serialization namespace) 
// that will serialize objects of type Movie. The XMLSerializer will serialize objects to a stream, 
// so we'll have to create one of those next. In this case, I want to serialize it to a file, so 
// I create a TextWriter. I then simply call Serialize on the XMLSerializer passing in the stream 
// (textWriter) and the object (movie). Lastly I close the TextWriter because you should always 
// close opened files. That's it! Let's create a movie object and see how this is used.

static void Main(string[] args)
{
  Movie movie = new Movie();
  movie.Title = "Starship Troopers";
  movie.ReleaseDate = DateTime.Parse("11/7/1997");
  movie.Rating = 6.9f;

  SerializeToXML(movie);
}

static public void SerializeToXML(Movie movie)
{
  XmlSerializer serializer = new XmlSerializer(typeof(Movie));
  TextWriter textWriter = new StreamWriter(@"C:\movie.xml");
  serializer.Serialize(textWriter, movie);
  textWriter.Close();
}

// After this code executes, we'll have an XML file with the contents of our movie object.

<?xml version="1.0" encoding="utf-8"?>
<Movie xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
   xmlns:xsd="http://www.w3.org/2001/XMLSchema">
  <Title>Starship Troopers</Title>
  <Rating>6.9</Rating>
  <ReleaseDate>1997-11-07T00:00:00</ReleaseDate>
</Movie>

// If you noticed, all of the XML tag names are the same as the property names. 
// If we want to change those, we can simply add an attribute above each property that sets the tag name.

public class Movie
{
  [XmlElement("MovieName")]
  public string Title
  { get; set; }

  [XmlElement("MovieRating")]
  public float Rating
  { get; set; }

  [XmlElement("MovieReleaseDate")]
  public DateTime ReleaseDate
  { get; set; }
}

// Now when the same code is executed again, we get our custom tag names.

<?xml version="1.0" encoding="utf-8"?>
<Movie xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
   xmlns:xsd="http://www.w3.org/2001/XMLSchema">
  <MovieName>Starship Troopers</MovieName>
  <MovieRating>6.9</MovieRating>
  <MovieReleaseDate>1997-11-07T00:00:00</MovieReleaseDate>
</Movie>

// Sometimes, in XML, you want information stored as an attribute of another tag instead of a tag by itself. 
// This can be easily accomplished with another property attribute.

public class Movie
{
  [XmlAttribute("MovieName")]
  public string Title
  { get; set; }

  [XmlElement("MovieRating")]
  public float Rating
  { get; set; }

  [XmlElement("MovieReleaseDate")]
  public DateTime ReleaseDate
  { get; set; }
}

// With this code, MovieName will now be an attribute on the Movie tag.

<?xml version="1.0" encoding="utf-8"?>
<Movie xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
   xmlns:xsd="http://www.w3.org/2001/XMLSchema"
   MovieName="Starship Troopers">
  <MovieRating>6.9</MovieRating>
  <MovieReleaseDate>1997-11-07T00:00:00</MovieReleaseDate>
</Movie>

// Let's move on to something a little more interesting. 
// Let's create another movie and serialize a List of them to our XML file. 
// Here's the modified code to do just that:

static void Main(string[] args)
{
  Movie movie = new Movie();
  movie.Title = "Starship Troopers";
  movie.ReleaseDate = DateTime.Parse("11/7/1997");
  movie.Rating = 6.9f;

  Movie movie2 = new Movie();
  movie2.Title = "Ace Ventura: When Nature Calls";
  movie2.ReleaseDate = DateTime.Parse("11/10/1995");
  movie2.Rating = 5.4f;

  List<Movie> movies = new List<Movie>() { movie, movie2 };

  SerializeToXML(movies);
}

static public void SerializeToXML(List<Movie> movies)
{
  XmlSerializer serializer = new XmlSerializer(typeof(List<Movie>));
  TextWriter textWriter = new StreamWriter(@"C:\movie.xml");
  serializer.Serialize(textWriter, movies);
  textWriter.Close();
}

// Now we have XML that looks like this:

<?xml version="1.0" encoding="utf-8"?>
<ArrayOfMovie xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
   xmlns:xsd="http://www.w3.org/2001/XMLSchema">
  <Movie MovieName="Starship Troopers">
    <MovieRating>6.9</MovieRating>
    <MovieReleaseDate>1997-11-07T00:00:00</MovieReleaseDate>
  </Movie>
  <Movie MovieName="Ace Ventura: When Nature Calls">
    <MovieRating>5.4</MovieRating>
    <MovieReleaseDate>1995-11-10T00:00:00</MovieReleaseDate>
  </Movie>
</ArrayOfMovie>

// Ok, so you can see how easy it is to get your objects into an XML document. 
// Let's now look at how to read an XML document back into our objects - deserialization. 
// The process of deserializing is very similar to what we did for serialization.

static List<Movie> DeserializeFromXML()
{
   XmlSerializer deserializer = new XmlSerializer(typeof(List<Movie>));
   TextReader textReader = new StreamReader(@"C:\movie.xml");
   List<Movie> movies;
   movies = (List<Movie>)deserializer.Deserialize(textReader);
   textReader.Close();

   return movies;
}

// Just like before, we first create an XmlSerializer that can deserialize objects of type List<Movie>. 
// The XmlSerializer also deserializes from a stream, so we create a file stream from our XML file. 
// We then simply call Deserialize on the stream and cast the output to our desired type. 
// Now the movies List is populated with objects that we previously serialized to the XML file.


// The deserializer is very good at handling missing pieces of information in your XML file. 
// Let's say the second movie didn't have the MovieName attribute on the Movie tag. 
// When the XML file is deserialized, it simply populates that field with null. 
// If MovieRating wasn't there, you'd receive 0. Since a DateTime object can't be null, 
// if MovieReleaseDate was missing, you'd receive DateTime.MinValue (1/1/0001 12:00:00AM).


// If the XML document contains invalid syntax, like say the first opening Movie tag was missing, 
// the Deserialize call will fail with an InvalidOperationException. 
// It will also be kind enough to specify the location in the file where it encountered 
// the error (line number, column number).


// One thing to remember is that the basic XML serialization won't maintain references. 
// Let's say I populated my movies list with the same movie reference multiple times:

Movie movie = new Movie();
movie.Title = "Starship Troopers";
movie.ReleaseDate = DateTime.Parse("11/7/1997");
movie.Rating = 6.9f;

List<Movie> movies = new List<Movie>() { movie, movie };


// Now I have a list containing two of the exact same movie reference. 
// When I serialize and deserialize this list, it will be converted to two separate 
// instances of the movie object - they would just have the same information. 
// Along this same line, the XMLSerializer also doesn't support circular references. 
// If you need this kind of flexibility, you should consider binary serialization.


// There's still a lot to cover when it comes to XML serialization,
//  but I think this tutorial covers enough of the basics to get things rolling. 
// If you've got questions or anything else to say, leave us a comment.