Object Serialization and De-Serialization

Imports System.IO

Public Class Exercise

    Private Sub btnWrite_Click(ByVal sender As System.Object, _
                               ByVal e As System.EventArgs) Handles btnWrite.Click
        Dim Make As String = txtMake.Text
        Dim Model As String = txtModel.Text
        Dim Year As Integer = CInt(txtYear.Text)
        Dim CarColor As Integer = cbxColors.SelectedIndex

        Dim stmCar As FileStream = New FileStream("Car1.car", FileMode.Create)
        Dim bnwCar As BinaryWriter = New BinaryWriter(stmCar)

        Try
            bnwCar.Write(Make)
            bnwCar.Write(Model)
            bnwCar.Write(Year)
            bnwCar.Write(CarColor)
        Finally
            bnwCar.Close()
            stmCar.Close()
        End Try
    End Sub
End Class

Here is an example of running the program:

This is an example of the techniques used in file processing to save individual data of primitive types:

The values can be retrieved with the following code:

Imports System.IO

Public Class Exercise

    Private Sub btnWrite_Click(ByVal sender As System.Object, _
                               ByVal e As System.EventArgs) Handles btnWrite.Click
        Dim Make As String = txtMake.Text
        Dim Model As String = txtModel.Text
        Dim Year As Integer = CInt(txtYear.Text)
        Dim CarColor As Integer = cbxColors.SelectedIndex

        Dim stmCar As FileStream = New FileStream("Car1.car", FileMode.Create)
        Dim bnwCar As BinaryWriter = New BinaryWriter(stmCar)

        Try
            bnwCar.Write(Make)
            bnwCar.Write(Model)
            bnwCar.Write(Year)
            bnwCar.Write(CarColor)
        Finally
            bnwCar.Close()
            stmCar.Close()
        End Try
    End Sub

    Private Sub btnRead_Click(ByVal sender As Object, _
                              ByVal e As System.EventArgs) Handles btnRead.Click
        Dim stmCar As FileStream = New FileStream("Car1.car", FileMode.Open)
        Dim bnrCar As BinaryReader = New BinaryReader(stmCar)

        Try
            txtMake.Text = bnrCar.ReadString()
            txtModel.Text = bnrCar.ReadString()
            txtYear.Text = bnrCar.ReadUInt32().ToString()
            cbxColors.SelectedIndex = bnrCar.ReadInt32()
        Finally
            bnrCar.Close()
            stmCar.Close()
        End Try
    End Sub
End Class

In the same way, you can save the individual fields of a class or you can retrieve the individual fields of a car:

Here is an example:

Public Class Car
    Public Make As String
    Public Model As String
    Public Year As Integer
    Public Color As Integer
End Class

Imports System.IO

Public Class Exercise

    Private Sub btnWrite_Click(ByVal sender As System.Object, _
                               ByVal e As System.EventArgs) Handles btnWrite.Click
        Dim Vehicle As Car = New Car()

        Vehicle.Make = txtMake.Text
        Vehicle.Model = txtModel.Text
        Vehicle.Year = CInt(txtYear.Text)
        Vehicle.Color = cbxColors.SelectedIndex

        Dim stmCar As FileStream = New FileStream("Car2.car", FileMode.Create)
        Dim bnwCar As BinaryWriter = New BinaryWriter(stmCar)

        Try
            bnwCar.Write(Vehicle.Make)
            bnwCar.Write(Vehicle.Model)
            bnwCar.Write(Vehicle.Year)
            bnwCar.Write(Vehicle.Color)
        Finally
            bnwCar.Close()
            stmCar.Close()
        End Try
    End Sub

    Private Sub btnRead_Click(ByVal sender As Object, _
                              ByVal e As System.EventArgs) Handles btnRead.Click
        Dim stmCar As FileStream = New FileStream("Car2.car", FileMode.Open)
        Dim bnrCar As BinaryReader = New BinaryReader(stmCar)

        Try
            Dim Vehicle As Car = New Car()

            Vehicle.Make = bnrCar.ReadString()
            Vehicle.Model = bnrCar.ReadString()
            Vehicle.Year = bnrCar.ReadUInt32()
            Vehicle.Color = bnrCar.ReadInt32()

            txtMake.Text = Vehicle.Make
            txtModel.Text = Vehicle.Model
            txtYear.Text = Vehicle.Year
            cbxColors.SelectedIndex = Vehicle.Color
        Finally
            bnrCar.Close()
            stmCar.Close()
        End Try
    End Sub
End Class

When it comes to a class, the problem with saving individual fields is that you could forget to save one of the fields. For example, considering a Car class, if you don't save the Make information of a Car object and retrieve or open the saved object on another computer, the receiving user would miss some information and the car cannot be completely identifiable. An alternative is to save the whole Car object.

Object serialization consists of saving a whole object as one instead of its individual fields:

In other words, a variable declared from a class can be saved to a stream and then the saved object can be retrieved later or on another computer. The .NET Framework supports two types of object serialization: binary and SOAP.

1. Start Microsoft Visual Basic and create a Windows Forms Application named RealEstate1
2. To create a new form, on the main menu, click Projects -> Add Windows Form...
3. Set the Name to PropertyEditor and click Add
4. Design the form as follows:
    

   Control Text Name Other Properties Label Property #:     TextBox   txtPropertyNumber Modifiers: Public Label Property Type:     ComboBox   cbxPropertyTypes Modifiers: Public Items: Unknown Single Family Townhouse Condominium Label Address:     TextBox   txtAddress Modifiers: Public Label City:     TextBox   txtCity Modifiers: Public Label State:     ComboBox   cbxStates Modifiers: Public Items: DC MD PA VA WV Label ZIP Code:     TextBox   txtZIPCode Modifiers: Public Label Bedrooms:     TextBox 0 txtBedrooms Modifiers: Public Label Bathrooms:     TextBox 1.0 txtBathrooms Modifiers: Public Label Market Value:     TextBox 0.00 txtMarketValue Modifiers: Public Button OK btnOK DialogResult: OK Button Cancel btnCancel DialogResult: Cancel
   Form
   FormBorderStyle:	FixedDialog
   Text:	Altair Realtors - Property Editor
   StartPosition:	CenterScreen
   AcceptButton:	btnOK
   CancelButton:	btnCancel
   MaximizeBox:	False
   MinimizeBox:	False
   ShowInTaskBar:	False

5. In the Solution Explorer, right-click Form1.vb and click Rename
6. Type RealEstate.vb and press Enter twice (to display that form)
7. Design the form as follows:
    

   Control Text Name Label Property #:   TextBox   txtPropertyNumber Button Open btnOpen Label Property Type:   TextBox   txtPropertyType Label Address:   TextBox   txtAddress Label City:   TextBox   txtCity Label State:   TextBox   txtState Label ZIP Code:   TextBox   txtZIPCode Label Bedrooms:   TextBox 0 txtBedrooms Label Bathrooms:   TextBox 1.0 txtBathrooms Label Market Value:   TextBox 0.00 txtMarketValue Button &New Property... btnNewProperty Button Close btnClose
   Form
   FormBorderStyle:	FixedDialog
   Text:	Altair Realtors - Property Editor
   StartPosition:	CenterScreen

8. Save the form

Binary serialization works by processing an object rather than streaming its individual member variables. This means that, to use it, you define an object and initialize it, or "fill" it, with the necessary values and any information you judge necessary. This creates a "state" of the object. It is this state that you prepare to serialize. When you save the object, it is converted into a stream.

To perform binary serialization, there are a few steps you must follow. When creating the class whose objects would be serialized, start it with the <Serializable> attribute. Here is an example:

<Serializable()> Public Class Car
    Public Make As String
    Public Model As String
    Public Year As Integer
    Public Color As Integer
End Class

Before serializing an object, you should reference the System.Runtime.Serialization.Formatters.Binary namespace. The class responsible for binary serialization is called BinaryFormatter. This class is equipped with two constructors. The default constructor is used to simply create an object.

After declaring the variable, to actually serialize an object, call the Serialize() method of the BinaryFormatter class. The method is overloaded with two versions. One of the versions of this method uses the following syntax:

Public Sub Serialize ( _
	serializationStream As Stream, _
	graph As Object _
)

The first argument to this method must be an object of a Stream-based class, such as a FileStream object. The second argument must be the object to serialize. This means that, before calling this method, you should have built the object.

Here is an example:

Imports System.IO
Imports System.Runtime.Serialization.Formatters.Binary

Public Class Exercise

    Private Sub btnWrite_Click(ByVal sender As System.Object, _
                               ByVal e As System.EventArgs) Handles btnWrite.Click
        Dim vehicle As Car = New Car()
        vehicle.Make = txtMake.Text
        vehicle.Model = txtModel.Text
        vehicle.Year = CInt(txtYear.Text)
        vehicle.Color = cbxColors.SelectedIndex

        Dim stmCar As FileStream = New FileStream("Car3.car", FileMode.Create)
        Dim bfmCar As BinaryFormatter = New BinaryFormatter()

        bfmCar.Serialize(stmCar, vehicle)
    End Sub
End Class

1. To create a new class, on the main menu, click Project -> Add Class...
2. Set the Name to SampleProperty and click Add
3. Change the file as follows:
    

   <Serializable()> Public Class SampleProperty Public PropertyNumber As String Public PropertyType As String Public Address As String Public City As String Public State As String Public ZIPCode As Integer Public Bedrooms As Short Public Bathrooms As Single Public MarketValue As Double End Class

4. In the Solution Explorer, right-click RealEstate.vb and click View Code
5. In the Class Name combo box, select (RealEstate Events)
6. In the Method Name combo box, select Click and change the file as follows:
    

   Imports System.IO Imports System.Runtime.Serialization.Formatters.Binary Public Class RealEstate Private Sub btnNewProperty_Click(ByVal sender As System.Object, _ ByVal e As System.EventArgs) _ Handles btnNewProperty.Click Dim Editor As PropertyEditor = New PropertyEditor Dim DirInfo As DirectoryInfo = _ Directory.CreateDirectory("C:\Altair Realtors\Properties") Dim RndNumber As Random = New Random Dim LeftNumber As Integer = RndNumber.Next(100, 999) Dim RightNumber As Integer = RndNumber.Next(100, 999) Editor.txtPropertyNumber.Text = LeftNumber.ToString() & "-" _ & RightNumber.ToString() If Editor.ShowDialog() = DialogResult.OK Then Dim Prop As SampleProperty = New SampleProperty prop.PropertyNumber = Editor.txtPropertyNumber.Text prop.PropertyType = Editor.cbxPropertyTypes.Text prop.Address = Editor.txtAddress.Text prop.City = Editor.txtCity.Text prop.State = Editor.cbxStates.Text prop.ZIPCode = CInt(Editor.txtZIPCode.Text) prop.Bedrooms = CInt(Editor.txtBedrooms.Text) prop.Bathrooms = CSng(Editor.txtBathrooms.Text) prop.MarketValue = CDbl(Editor.txtMarketValue.Text) Dim strFilename As String = DirInfo.FullName & "\" & _ Editor.txtPropertyNumber.Text & ".prp" Dim stmProperty As FileStream = New FileStream(strFilename, _ FileMode.Create, FileAccess.Write) Dim bfmProperty As BinaryFormatter = New BinaryFormatter bfmProperty.Serialize(stmProperty, prop) End If End Sub End Class

7. In the Class Name combo box, select btnClose
8. In the Method name combo box, select Click and implement the event as follows:
    

   Private Sub btnClose_Click(ByVal sender As Object, _ ByVal e As System.EventArgs) _ Handles btnClose.Click End End Sub

9. Execute the application and continuously click the New Property button to create the following properties (let the computer specify the property number):
      

   Property Type	Address	City	State	ZIP Code	Beds	Baths	Market Value
   Single Family	11604 Aldora Avenue	Baltimore	MD	21205	5	3.5	325650
   Townhouse	495 Parker House Terrace	Gettysburg	WV	26201	3	2.5	225500
   Condominium	5900 24th Street NW #812	Washington	DC	20008	1	1.0	388665
   Single Family	6114 Costinha Avenue	Martinsburg	WV	25401	4	3.5	325000
   Condominium	10710 Desprello Street #10D	Rockville	MD	20856	1	1.0	528445

10. Close the form and return to your programming environment

As serialization is the process of storing an object to a medium, the opposite, de-serialization is used to retrieve an object from a stream. To support this, the BinaryFormatter class is equipped with the Deserialize() method. Like Serialize(), the Deserialize() method is overloaded with two versions. One of them uses the following syntax:

Public Function Deserialize ( _
	serializationStream As Stream _
) As Object

This method takes as argument a Stream-based object, such as a FileStream variable, that indicates where the file is located. The Deserialize() method returns an Object object. As a goal, you want the Deserialize() method to produce the type of object that was saved so you can retrieve the values that the returned object holds. Because the method returns an Object value, you must cast the returned value to the type of your class.

Once the Deserialize() method has returned the desired object, you can access its values. Here is an example:

Imports System.IO
Imports System.Runtime.Serialization.Formatters.Binary

Public Class Exercise

    Private Sub btnWrite_Click(ByVal sender As System.Object, _
                               ByVal e As System.EventArgs) Handles btnWrite.Click
        Dim Vehicle As Car = New Car()

        Vehicle.Make = txtMake.Text
        Vehicle.Model = txtModel.Text
        Vehicle.Year = CInt(txtYear.Text)
        Vehicle.Color = cbxColors.SelectedIndex

        Dim stmCar As FileStream = New FileStream("Car3.car", FileMode.Create)
        Dim bfmCar As BinaryFormatter = New BinaryFormatter()

        bfmCar.Serialize(stmCar, vehicle)
    End Sub

    Private Sub btnRead_Click(ByVal sender As Object, _
                              ByVal e As System.EventArgs) Handles btnRead.Click
        Dim stmCar As FileStream = New FileStream("Car3.car", FileMode.Open)
        Dim bnrCar As BinaryReader = New BinaryReader(stmCar)

        Dim bfmCar As BinaryFormatter = New BinaryFormatter()
        Dim Vehicle As Car = CType(bfmCar.Deserialize(stmCar), Car)

        txtMake.Text = Vehicle.Make
        txtModel.Text = Vehicle.Model
        txtYear.Text = Vehicle.Year.ToString()
        cbxColors.SelectedIndex = Vehicle.Color
    End Sub
End Class

1. In the Class Name combo box, select btnOpen
2. In the Method name combo box, select Click and implement the event as follows:
    

   Private Sub btnOpen_Click(ByVal sender As Object, _ ByVal e As System.EventArgs) _ Handles btnOpen.Click Dim DirProperties As DirectoryInfo = _ New DirectoryInfo("C:\Altair Realtors\Properties") Dim FleProperties() As FileInfo = DirProperties.GetFiles() If DirProperties.Exists = True Then Dim Found As Boolean = False Dim Prop As SampleProperty = Nothing Dim fle As FileInfo For Each fle In FleProperties Dim stmProperty As FileStream = _ New FileStream(fle.FullName, _ FileMode.Open, _ FileAccess.Read) Dim bfmProperty As BinaryFormatter = New BinaryFormatter() Prop = CType(bfmProperty.Deserialize(stmProperty), _ SampleProperty) If Prop.PropertyNumber = txtPropertyNumber.Text Then Found = True End If Next If Found = True Then txtPropertyType.Text = Prop.PropertyType txtAddress.Text = Prop.Address txtCity.Text = Prop.City txtState.Text = Prop.State txtZIPCode.Text = Prop.ZIPCode txtBedrooms.Text = Prop.Bedrooms txtBathrooms.Text = FormatNumber(Prop.Bathrooms) txtMarketValue.Text = FormatNumber(Prop.MarketValue) Else MsgBox("There is no property with " & _ "that number in our database") txtPropertyType.Text = "Unknown" txtAddress.Text = "" txtCity.Text = "" txtState.Text = "" txtZIPCode.Text = "00000" txtBedrooms.Text = "0" txtBathrooms.Text = "0.00" txtMarketValue.Text = "0.00" End If End If End Sub

3. Execute the application and try opening a previously save property using its number
4. Close the form and return to your programming environment

In the examples we have used so far, we were saving the whole object. You can make it possible to save only some parts of the class. When creating a class, you can specify what fields would be serialized and which ones would not be. To specify that a member cannot be saved, you can mark it with the <NonSerialized()> attribute. Here is an example:

<Serializable()> Public Class Car1
    Public Make As String
    Public Model As String

    ' Because the value of a car can change,
    ' there is no reason to save it
    <NonSerialized()> _
    Public Value As Double
    Public Year As Integer
    Public Color As Integer
End Class

After creating the class, you can declare a variable of it and serialize it, using either the binary or the SOAP approach. You can then retrieve the object and its values, using any of the techniques we learned earlier.

To support serialization, the .NET Framework provides the ISerializable interface. You can create a class that implements this interface to customize the serialization process. Even if you plan to use this interface, the class you create must be marked with the <Serializable> attribute.

The .NET Framework is filled with many classes ready for serialization. To know that a class is ready for serialization, when viewing its documentation either in the MSDN web site or in the help documentation, check that it is marked with the [SerializableAttribute]. Here is an example of such as class: