MCTS Exam 70-536 – Serialization | DotNetBlog der DotNet-Blog

MCTS Exam 70-536 – Serialization

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Its getting hot in here … so, I scheduled my exam – Wish me luck. Till then, I will try to catch-up on my writing cause I think this is a very efficient way for last minute learning – Today’s topic is serialization. Enjoy!

Common

Serialization is implemented in the System.Runtime.Serialization-namespace
objects can be stored or transferred and then be recreated
Serialization High-Level steps are the following
- Create a stream object to hold the output
- Create a BinaryFormatter object (in System.Runtime.Serialization.Formatters.Binary)
- Call the BinaryFormatter.Serialize
with BinaryFormatter, output will be stored as ASCII text
Deserialization High-Level steps are the following
- Create a stream object to read
- Create a BinaryFormatter object (in System.Runtime.Serialization.Formatters.Binary)
- Create a new object to hold the deserialized data
- Call BinaryFormatter.Deserialize

Serializable Class

Make a class serializable, by adding the Serializable Attribute to it
Even if you don’t need it now, its good practice to enable it anyway
You can disable serialization of members with the NonSerialized Attribute in front of them
To initialize non-serialized members automatically on deserialization, implement the IDeserializationCallback interface and implement the OnDeserializationCallback-method.
Version Compatibility can be reached by adding the OptionalField Attribute to a member added. So also previously serialized versions of the class can be deserialized properly
Best Practice:
- Never remove a serialized member
- Never apply NonSerialized to a field that didn’t have this attribute in the previous version
- Never change the name or the type of a serialized field
- apply OptionalField to new fields (also, if you remove NonSerialized -Attribute)
- Set meaningful default values for all optional fields Using callbacks
There are different Serialization-Formats
- BinaryFormatter – Most efficient for objects, only readable by .NET Apps
- SoapFormatter – Most reliable, if not only .NET Apps are consuming. XML based. Objects is consuming 3 or 4 times more space.
Control Soap Serialization with the following attributes
- SoapAttribute – Class member will be serialized as XML attribute
- SoapDefaultValue – default value of member
- SoapElement – member will be serialized as XML element (node)
- SoapEnum – element name of an enumeration member
- SoapIgnore – ignore the field
- SoapType – schema for the xml that is generated
Guidelines
- when in double, mark a class as Serializable
- mark temporary or calculated members as NonSerialized
- use SoapFormatter for portability, use BinaryFormatter for efficiency

XML Serialization

Use it, when you need to exchange objects with non .NET applications.
Following Benefits above standard serialization:
- Greater interoperability
- More admin-friendly – objects serialized can be viewed in notepad
- Better forward-compatibility – xml is self describing
Use XML Serialization to be conform to an XSD
Limitations are
- can only serialize public data
- can not serialize object graphs, only objects
Steps to use XML Serialization
- Create stream, TextWriter or XmlWriter to hold output
- Create XmlSerializer and pass the type of the object you want to serialize
- Call XmlSerializer.Serialize to serialize the object
Steps to use Deserialization
- Create stream, TextReader or XmlReader to read the input
- Create an XmlSerializer object by passing the type
- Call XmlSerializer.Deserialize method
To create a class that can be serialized with XmlSerializer do the following
- Specify the class as public
- Specify all members you want to serialize as public
- Create a parameterless constructor
How to control Xml Serialization
- Use he following Attributes to tag the members of your class
  - XmlAnyAttribute – when deserializing, array will be filled with XmlAttributes unknown to the schema
  - XmlAnyElement – same as XmlAnyAttribute but with elements
  - XmlArray – members of the array will be generated as members of an Xml array
  - XmlArrayItem – derived types can be inserted into an array – usually in conjunction with XmlArray
  - XmlAttribute – Member will be serialized as Xml attribute
  - XmlChoiceIdentifier – member can be disambiguated by using an array
  - XmlElement – Member will be serialized as Xml Element
  - XmlEnum – Element name of an enumeration member
  - XmlIgnore – Similar to NonSerialized, ignore member while serializing
  - XmlInclude – Include class when schema generated to recognize when serialize
  - XmlRoot – Specifying namespace or element name of root
  - XmlText – Serialized as Xml text
  - XmlType – name and namespace of XmlType
- Example to attributes
  
  [XmlRoot(“ShoppingItem”]
  public class CartItem
  {
  
  [XmlAttribute] public int userId;
Complete control can be reached by implementing IXmlSerializable interface in your class, and implement ReadXml and WriteXml methods
Avoid inflation by using Base64 encoding
When possible, leverage an exiting Xml Schema
Run the Xsd.exe-Tool to create classes that are strongly typed to a schema (ex. Xsd.exe schema.xsd / classes / language;[CS|VB])
You can also serialized DataSets and Collections

Custom Serialization

implement ISerializable interface and apply Serializable attribute to class
Use CS, if the class has declarative or imperative security at class level or its constructor
Implement GetObjectData and a special constructor (used for deserialization)
Populate SerializationInfo in GetObjectData method – Add values as Key/Value pair using AddValue (Creates internal SerializationEntry structure)
In constructor, fill members with values provided
You can use different IFormatterConverter Implementations in SerializationInfo constructor
Throw an SerializationException if invalid data is provided

Serialization Events

.NET supports serialization events when using BinaryFormatter (Only for this)
For SoapFormatter and custom serialization you are limited to use IDeserializationCallback-Interface events. they are
- Serializing – just before serializing. Apply OnSerialization-attribute to the method that should run.
- Serialized – after serializiation. Apply OnSerialized-attribute.
- Deserializing – just before deserializing. Apply OnDeserializing-attribute.
- Deserialized – after deserializing. Apply OnDeserialized-attribute. You should use OnDeserialization instead when not using BinaryFormatter.
The sequence is the same then in the list, but OnDeserialization will fire BEFORE OnDeserialized
Methods do not alter serialization stream, but you can modify the object.
The methods applied to the Callback-events must meet the following criteria
- Accept StreamingContext object as a parameter
- return void
- Have the corresponding attribute (as described before)

Change Serialization based on Context

Context may be the destination, so you probably want to serialize differently.
StreamingContext provides information about the current context
It has two properties
- Context – the context information (individual)
- State – indicating the source (deserialization) or destination(serialization) of the object being serialized/deserialized
  - CrossProcess – different process, same machine
  - CrossMachine – different machine
  - File – source or destination is file
  - Persistence – store such as database, file etc.
  - Remoting – remoting to unknown location
  - Other – unknown
  - Clone – object being cloned
  - CrossAppDomain – different AppDomain
  - All – might be any of the above
Make sure to set the context information in the Formatter before calling Serialize or Deserialize