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.

The .NET Framework supports a technique of serialization referred to as SOAP (which stands for Simple Object Access Protocol). This technique is a related to XML but, although we haven't studied XML, you don't need to know anything about it to use SOAP serialization.

1. Start a new Windows Application named Loan1
2. In the Solution Explorer, right-click Form1.vb and click Rename
3. Type LoanPreparation.vb and press Enter
4. Design the form as followed:
    

   Control Name Text Additional Properties GroupBox   Loan Identification   Label   Prepared &By:   TextBox txtEmployeeName     Label   Customer First Name:   TextBox txtCustomerFirstName     Label   Last Name:   TextBox txtCustomerLastName     GroupBox   Loan Preparation   Label   Principal:   TextBox txtPrincipal 0.00 TextAlign: Right Label   Interest Rate:   TextBox txtInterestRate 8.25 TextAlign: Right Label   %   Label   Periods:   TextBox txtPeriods 1 TextAlign: Text ComboBox cbxPeriods Months Items: Years Months Days GroupBox   Results   Button btnCalculate Calculate   Label   Interest Earned:   TextBox txtInterestEarned 0.00 TextAlign: Right ReadOnly: True Label   Amount Earned:   TextBox txtFutureValue 0.00 TextAlign: Right ReadOnly: True GroupBox   File Processing   Label   Loan ID:   TextBox txtSave     Button &Save btnSave   Label   Loan ID:   TextBox txtOpen     Button &Open btnOpen   Button btnClose Close

5. Right-click the form and click View Code
6. In the Class Name combo box, select txtCustomerLastName
7. In the Method Name combo box, select Leave and implement the event as follows:
    

   Private Sub txtCustomerLastName_Leave(ByVal sender As Object, _ ByVal e As System.EventArgs) _ Handles txtCustomerLastName.Leave Dim Initials As String = "00" Dim FirstName As String = txtCustomerFirstName.Text Dim LastName As String = txtCustomerLastName.Text If LastName.Length = 0 Then MsgBox("You must enter a last name") txtCustomerLastName.Focus() Exit Sub End If If FirstName.Length = 0 Then Initials = LastName.Substring(0, 1) & "1" Else Initials = FirstName.Substring(0, 1) & LastName.Substring(0, 1) End If txtSave.Text = Initials End Sub

8. In the Class Name combo box, select btnCalculate
9. In the Method Name combo box, select Click and implement the event as follows:
    

   Private Sub btnCalculate_Click(ByVal sender As Object, _ ByVal e As System.EventArgs) _ Handles btnCalculate.Click Dim Principal As Double Dim InterestRate As Double Dim InterestEarned As Double Dim FutureValue As Double Dim Periods As Double ' Retrieve the value of the principal Try Principal = CDbl(txtPrincipal.Text) Catch ex As FormatException MsgBox("The value you entered for the principal " & _ "is not valid.\nPlease try again") End Try ' Retrieve the interest rate Try InterestRate = CDbl(txtInterestRate.Text) / 100 Catch ex As FormatException MsgBox("The value you entered for the interest " & _ "rate is not valid\nPlease try again") End Try ' Get the number of periods Try If cbxPeriods.SelectedIndex = 0 Then ' Years Periods = CDbl(txtPeriods.Text) ElseIf cbxPeriods.SelectedIndex = 1 Then ' Months Periods = CDbl(txtPeriods.Text) / 12 Else ' if cbxPeriods.SelectedIndex = 2) Days Periods = CDbl(txtPeriods.Text) / 360 End If Catch ex As FormatException MsgBox("The value you entered for the number " & _ "of periods is not valid\nPlease try again") End Try Dim InterestRatePeriods As Double = InterestRate * Periods Dim InterestPlus1 As Double = InterestRatePeriods + 1 FutureValue = Principal * InterestPlus1 InterestEarned = FutureValue - Principal txtInterestEarned.Text = FormatNumber(InterestEarned) txtFutureValue.Text = FormatNumber(FutureValue) End Sub

10. Execute the application to make sure it is fine
11. After using it, close the form and return to your programming environment

To serialize an object using SOAP, you follow the same steps we reviewed for the binary serialization with one addition: you must add a certain reference.

When creating the class whose objects would be serialized, mark 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

To support SOAP serialization, the .NET Framework provides the SoapFormatter class. This class is defined in the System.Runtime.Serialization.Formatters.Soap namespace that is part of the System.Runtime.Serialization.Formatters.Soap.dll assembly. In order to use The SoapFormatter class, you must reference this assembly. Then, you can create an object and initialize it as you see fit. Before saving it, as always, create a Stream-based object that would indicate the name (and location) of the file and the type of action to perform. Then, declare a SoapFormatter dim as iable using its default constructor. To actually save the object, call the Serialize() method of this class. This method uses the same syntax as that of the BinaryFormatter class: it takes two arguments. The first is a Stream-based object. The second is the object that needs to be serialized.

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

   <Serializable()> Public Class LoanInformation Public EmployeeName As String Public CustomerFirstName As String Public CustomerLastName As String Public Principal As Double Public InterestRate As Double Public Periods As Double Public PeriodType As Integer End Class

4. To add SOAP support to your project, on the main menu, click Project -> Add Reference...
5. In the Add Reference dialog box and in the .NET tab, scroll down and select System.Runtime.Serialization.Formatters.Soap:
    
   
6. Click OK
7. Access the LoanPreparation.vb code file
8. In the top section of the form, type the following:
    

   Imports System.IO Imports System.Runtime.Serialization.Formatters.Soap Public Class LoanPreparation

9. In the Class Name combo box, select btnSave
10. In the Method Name combo box, select Click and implement the event as follows:
     

    Private Sub btnSave_Click(ByVal sender As Object, _ ByVal e As System.EventArgs) _ Handles btnSave.Click If txtSave.Text.Length = 0 Then MsgBox("Please enter the customer " & _ "initials or a name for the loan") txtSave.Focus() Exit Sub End If Dim infLoan As LoanInformation = New LoanInformation infLoan.EmployeeName = txtEmployeeName.Text infLoan.CustomerFirstName = txtCustomerFirstName.Text infLoan.CustomerLastName = txtCustomerLastName.Text infLoan.Principal = CDbl(txtPrincipal.Text) infLoan.InterestRate = CDbl(txtInterestRate.Text) infLoan.Periods = CDbl(txtPeriods.Text) infLoan.PeriodType = cbxPeriods.SelectedIndex Dim stmLoan As FileStream = New FileStream(txtSave.Text, _ FileMode.Create, _ FileAccess.Write) Dim sfmLoan As SoapFormatter = New SoapFormatter Try sfmLoan.Serialize(stmLoan, infLoan) txtEmployeeName.Text = "" txtCustomerFirstName.Text = "" txtCustomerLastName.Text = "" txtPrincipal.Text = "0.00" txtInterestRate.Text = "0.00" txtPeriods.Text = "0" cbxPeriods.SelectedIndex = 0 txtFutureValue.Text = "0.00" txtInterestEarned.Text = "0.00" txtSave.Text = "" txtOpen.Text = "" txtEmployeeName.Focus() Finally stmLoan.Close() End Try End Sub

11. Press Ctrl + F5 to execute the application
12. Create, calculate, and save a few loans
     
13. Close the form and return to your programming environment

De-serialization in soap is performed exactly as done for the binary de-serialization. To support it, the SoapFormatter class is equipped with the Deserialize() method. This method uses the same syntax as its equivalent of the BinaryFormatter class. The approach to use it is also the same.

1. In the Class Name combo box, select btnOpen
2. In the Method Name combo box, select Click
3. To deserialize, implement the event as follows:
    

   Private Sub btnOpen_Click(ByVal sender As Object, _ ByVal e As System.EventArgs) _ Handles btnOpen.Click If txtOpen.Text.Length = 0 Then MsgBox("Please enter a customer's initials or " & _ "a name given to a previous loan preparation") txtOpen.Focus() Exit Sub End If Try Dim LoanInfo As LoanInformation = New LoanInformation Dim LoanStream As FileStream = New FileStream(txtOpen.Text, _ FileMode.Open, _ FileAccess.ReadWrite) Dim LoanFormatter As SoapFormatter = New SoapFormatter Try ' Open the file and store its values ' in the LoanInformation variable LoanInfo = CType(LoanFormatter.Deserialize(LoanStream), _ LoanInformation) ' Retrive each value and put it in its corresponding control txtEmployeeName.Text = LoanInfo.EmployeeName txtCustomerFirstName.Text = LoanInfo.CustomerFirstName txtCustomerLastName.Text = LoanInfo.CustomerLastName txtPrincipal.Text = LoanInfo.Principal.ToString("F") txtInterestRate.Text = LoanInfo.InterestRate.ToString("F") txtPeriods.Text = LoanInfo.Periods.ToString() cbxPeriods.SelectedIndex = LoanInfo.PeriodType ' Since we didn't save the calculated values, ' call the Click event of the Calculate button btnCalculate_Click(sender, e) Finally LoanStream.Close() End Try Catch ex As FileNotFoundException MsgBox("There is no file with that name") End Try End Sub

4. In the Class Name combo box, select btnOpen
5. 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

6. Press Ctrl + F5 to execute the application
7. Enter the initials of a previously created loan and click Open
8. 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: