Serialization

Introduction to Serialization

Serialization is a technique used to convert an object (or struct) into a stream of bytes for easy storage or transmission. This process can be reversed using deserialization, which recreates the object from the serialized data. Serialization is useful for saving the state of objects, transmitting data over networks, or sharing data between different applications.

Types of Serialization

There are two main types of serialization:

Binary Serialization: Converts objects into a binary format. It's efficient but not human-readable. Note that Microsoft no longer recommends using the BinaryFormatter class due to security concerns. Instead, alternatives like BinaryWriter and BinaryReader should be used.

See Microsoft's security guidance for more details.

Human-Readable Serialization: Converts objects into text formats like XML or JSON, making them easier to read and edit manually. The XmlSerializer and JsonSerializer classes are commonly used for this purpose.

When to Use Serialization

Serialization is the preferred method for saving objects and structs to files because it automatically handles the conversion of complex data types into a storable format. Understanding serialization is important for various tasks such as:

Persisting application state.
Transferring data between different applications or systems.
Storing configuration settings or user data.

XML Serialization in C#

C# provides the XmlSerializer class in the System.Xml.Serialization namespace for serializing objects to and from XML format. This allows you to save objects in a structured, human-readable way.

Example: Serializing and Deserializing an Object

Let's look at how to serialize and deserialize a Book object using XmlSerializer.

Create a Book Object:

Book book = new Book();
book.Id = 1;
book.Title = "Wind in the Willows";
book.Author = "Kenneth Grahame";
book.Price = 9.99;
book.Year = 1908;

Serialize the Object:

using(XmlWriter writer = XmlWriter.Create("books.xml"))
{
    XmlSerializer serializer = new XmlSerializer(typeof(Book));
    serializer.Serialize(writer, book);
}

Deserialize the Object:

using(XmlReader reader = XmlReader.Create("books.xml"))
{
    XmlSerializer serializer = new XmlSerializer(typeof(Book));
    book = (Book)serializer.Deserialize(reader);
}

// Output the book details
Console.WriteLine(book.Title);
Console.WriteLine(book.Author);
Console.WriteLine(book.Price);
Console.WriteLine(book.Year);

Explanation

Creating the Book Object: Initialize a Book object with default values.
Serialization:
Create an XmlWriter object to write to books.xml.
Instantiate an XmlSerializer with the type of object to serialize (Book in this case).
Call Serialize() method, passing in the writer and the book object.

This converts the Book object into XML format and writes it to the file books.xml.

Deserialization:
Create an XmlReader object to read from books.xml.
Use the XmlSerializer to deserialize the XML back into a Book object.
Output the book details to verify that the object has been correctly reconstructed.

Key Points to Remember

Namespace: Include using System.Xml.Serialization; to access the XmlSerializer class.
Object Type: You must specify the type of the object being serialized (typeof(Book) in this example).
File Handling: Always close or dispose of the writer and reader objects after use to release file handles and resources.
Struct Visibility: Ensure the Book struct or class is public and accessible by the serializer.

Common Issues and Solutions

Class or Struct Visibility:
The class or struct you are serializing must be public.
If defined within the same file as the main program, move it to a separate file with the same namespace.

public struct Book
{
    public int Id;
    public string Title;
    public string Author;
    public double Price;
    public int Year;
}

Missing Default Constructor:
Ensure the class or struct has a parameterless constructor if it is not a simple struct.
Unsupported Types:
Ensure that only serializable types are used as fields or properties of the class/struct.

Next Steps

We will see the same process being used for JSON files in the next section. JSON is another popular format for serializing objects due to its lightweight and easy-to-read structure.

Exercises

Create a Student class with fields like Id, Name, Course, and Grade. Write a program to serialize and deserialize a list of students to/from an XML file.
Modify the Book example to include a list of reviews for each book. Update the serialization code to handle this nested structure.
Explore the use of DataContractSerializer for more control over the serialization process.