Advanced .NET Framework Topics

Serialization

What is Serialization

•
Serialization is the process of converting an
object, or a connected graph of objects, stored
within computer memory, into a linear sequence
of bytes

•
Use the sequence of bytes in several ways:

–
Send it to another process

–
Send it to the clipboard, to be browsed or used by
another application

–
Send it to another machine

–
Send it to a file on disk

Serialization

Object Graph

•
What is an object graph?

–
An object graph is a set of objects with some set
of references to each other

–
The most obvious problem is how to represent the
links between the objects in the Serialized stream

Cat

Cat

Mouse

Duck

Dog

2

1

3

4

9

7

Horse

Serialization

How Serialization Works

•
Because run
-
time metadata 'knows' about each object's
layout in memory, and its field and property definitions, you
can serialize objects automatically, without having to write
code to serialize each field

•
The serialized stream might be encoded using XML, or a
compact binary representation

•
The format is decided by the the Formatter object that you
call:

–
Binary

–
SOAP

–
Custom

Serializaiton

Example
-

VideoLibrary

using

System;




namespace

VideoLibrary

{




[
Serializable
]




public

enum

Genre

{ Drama, Comedy, Western,
ScienceFiction
, Horror, Family };





[
Serializable
]




public

class

VideoInfo



{







public

string

Title {
get
;
set
; }








public

Genre

Category {
get
;
set
; }








public

string

Director {
get
;
set
; }







public

int

Year {
get
;
set
; }








public

TimeSpan

Duration {
get
;
set
; }








public

string

Review {
get
;
set
; }



}


}

Worksheet 4 from
http://www.cse.ohio
-
state.edu/~crawfis/cse459_CSharp/index.html


Serializaiton

Example
-

VideoLibrary

namespace

VideoLibrary

{




public

partial

class

MyVideoLibraryForm

:
Form



{








List
<
VideoInfo
>
videoLib

=
new

List
<
VideoInfo
>();

…







private

void

saveLibraryToolStripMenuItem_Click
(
object

sender,
EventArgs

e)






{










if

(
this
.saveLibraryDialog.ShowDialog
() ==
DialogResult
.OK
)








{












XmlSerializer

s =
new

XmlSerializer
(
videoLib.GetType
());












using

(
TextWriter

w =
new

StreamWriter
(
saveLibraryDialog.FileName
))










{
















s.Serialize
(w,
videoLib
);












}










}








}


Worksheet 4 from
http://www.cse.ohio
-
state.edu/~crawfis/cse459_CSharp/index.html


File
-
>Save
menu

Serializaiton

Example
-

VideoLibrary







private

void

openToolStripMenuItem_Click
(
object

sender,
EventArgs

e)






{










if

(
this
.openLibraryDialog.ShowDialog
() ==
DialogResult
.OK
)








{












XmlSerializer

s =
new

XmlSerializer
(
videoLib.GetType
());












using

(
TextReader

reader =
new

StreamReader
(
openLibraryDialog.FileName
))










{
















List
<
VideoInfo
>
newVideos

= (
List
<
VideoInfo
>)
s.Deserialize
(reader);
















foreach
(
VideoInfo

video
in

newVideos
)


















bindingVideoLib.Add
(video);












}










}








}

Worksheet 4 from
http://www.cse.ohio
-
state.edu/~crawfis/cse459_CSharp/index.html


File
-
>Import
menu

Serialization

Scenarios

•
Persistence

•
Remoting
-
By
-
Value

•
Remoting
-
By
-
Reference

•
Transacted Persistence


Serialization

Basic Serialization

•
A Type is NOT Serializable unless Type is
specifically marked as Serializable

•
The Serializable Attribute



•
The Non
-
Serializable Attribute



[Serializable] public class MyClass {}


[Serializable] public class MyClass {


[NotSerialized] int _cashSize;

}

Serialization

•
It is easy to write the individual fields of a
record

object to
a file

•
For example, we can create a record that stores
information about a student

–
Name

–
Address

–
ID number

–
Course enrolled for

–
etc

•
We can output each field of this record to a file (either
text or binary)

Serialization

StudentInfo

Name

Address

ID number

Course Info

Record file

string
string

int

string

Serialization

•
In this example, any program that needs to read the
file needs to know the format of the data

–
2 strings, an
int

and then a string

–
Also whether each item is on a separate line

•
.NET serialization

allows complete objects to be read
or written with a single statement (.NET does the
plumbing for you using reflection).

•
A
serialized object

is an object represented as a
sequence of bytes.

•
Information is stored about the data types of the
objects instance fields as well as their values

–
Allows the object to be reconstructed (de
-
serialized) from the sequence of bytes.

Serialization

StudentInfo

Name

Address

ID number

Course Info

Record file

StudentInfo object

Serialization

•
To serialize an object, the object class needs to be
marked with the
[
Serializable
]
attribute or needs
to implement the
ISerializable

interface

•
Requires the
System.Runtime.Serialization

namespace

•
Also we require a formatter to serialize/de
-
serialize the object before writing to or reading
from file

–
IFormatter

-

BinaryFormatter

–
XMLSerializer

(why is this not an
IFormatter
?)

Serialization

ISerializable

Interface

•
Customize the serialization process

•
If a class implements ISerializable, that
interface will always be called in preference to
default serialization.

•
The ISerializable interface only contains one
method:



void

GetObjectData

(
SerializationInfo

info,
StreamingContext

context);

And
an implied constructor that may be private.



private

<T>
(
SerializationInfo

info,
StreamingContext
)

Serialization

Additional Attributes

•
The serialization framework allows you to also
specify methods to be called when an instance
is being
deserialized
, after it is
deserialized
,
before it is serialized, etc.

–
[
OnDeserialized
]
–

see the
MSDN example
.

Serialization

IDeserializationEventListener

•
If an object implements
IDeserializationEventListener, the serialization
infrastructure will call that class‘
OnDeserialization method as soon as the

entire graph has been deserialized and all fix
-
ups completed

•
Provide a reasonable opportunity for objects

that need to do fix
-
ups based on the state of
their children


Serialization

•
Binary serialization is limited as only .NET
applications can
deserialize

the data stream

•
For more general inter
-
operability
especially across a network,
xml
serialization

is used

–
xml is text based and self
descibing

and
universal

–
Comprised name/attribute pairs

–
xml serialization easy to implement and uses
text streams

Serialization

•
We need to insert xml tags into our
StudentInfo


class

–
Only public properties and fields can be
serialized

[
XmlRoot
("
studentInfo
")]

public class
StudentInfo

{



[
XmlAttribute
("name")] public string Name;



[
XmlAttribute
("address")] public string Address;



[
XmlAttribute
("course")] public string
CourseInfo
;



[
XmlAttribute
("id")] private
int

ID;





public
StudentInfo
()



{ }




public
StudentInfo
(String n, String a, String
ci
,
int

id)



{



Name = n; Address = a;
CourseInfo

=
ci
;



ID = id;



}

}