Visual Basic .NET File Processing - Lesson 3: Binary File Streaming

	Binary File Streaming

Introduction to File Streaming

File streaming consists of performing one of the routine operations on a file, such as creating or opening it. This basic operation can be performed using a class called FileStream. You can use a FileStream object to get a stream ready for processing. As one of the most complete classes of file processing of the .NET Framework, FileStream is equipped with all necessary properties and methods. To use it, you must first declare a variable of it. The class is equipped with nine constructors.

One of the constructors (the second) of the FileStream class has the following syntax:

Public Sub New(ByVal path As String, ByVal mode As FileMode)

This constructor takes as its first argument the name of the file or its path. The second argument specifies the type of operation to perform on the file. Here is an example:

Private Sub btnStart_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) _
			Handles btnStart.Click
        Dim fileName As String = "Persons.spr"

        Dim fstPersons As FileStream = New FileStream(fileName, FileMode.Create)
End Sub

Practical Learning: Introducing File Streaming

Create a new Windows Forms Application named ROSH1

Design the form as follows:

Control	Name	Text	Other Properties
GroupBox		Identification
Label		Student Name:
TextBox	txtStudentName
Label		School Year:
TextBox	txtSchoolYear1
Label		/
TextBox	txtSchoolYear2
GroupBox		Grades
Label		English:
TextBox	txtEnglish	0.00
Label		History:
TextBox	txtHistory	0.00
Label		Economics:
TextBox	txtEconomics	0.00
Label		2nd Language:
TextBox	txt2ndLanguage	0.00
Label		Geography:
TextBox	txtGeography	0.00
Label		Arts:
TextBox	txtArts	0.00
Label		Math:
TextBox	txtMath	0.00
Label		Science:
TextBox	txtScience	0.00
Label		Phys Educ:
TextBox	txtPhysEduc	0.00
GroupBox		Grade Processing
Button	btnCalculate	Calculate
Label		Total:
TextBox	txtTotal	0.00
Label		Average:
TextBox	txtAverage	0.00
Button	btnSave	Save
Button	btnOpen	Open
Button	btnClose	Close

Double-click the Calculate button and implement its Click event as follows:

Private Sub btnCalculate_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) _
			Handles btnCalculate.Click
        Dim english As Double
        Dim history As Double
        Dim economics As Double
        Dim language2 As Double
        Dim geography As Double
        Dim arts As Double
        Dim math As Double
        Dim science As Double
        Dim physEduc As Double
        Dim total As Double
        Dim average As Double

        ' Retrieve the value entered for each course
        Try
            english = CDbl(Me.txtEnglish.Text)
        Catch ex As FormatException
            MsgBox("The value you entered for the English course is not valid")
            Me.txtEnglish.Focus()
        End Try

        Try
            history = CDbl(Me.txtHistory.Text)
        Catch ex As FormatException
            MsgBox("The value you entered for the History course is not valid")
            Me.txtEnglish.Focus()
        End Try

        Try
            economics = CDbl(Me.txtEconomics.Text)
        Catch ex As FormatException
            MsgBox("The value you entered for the Economics course is not valid")
            Me.txtEnglish.Focus()
        End Try

        Try
            language2 = CDbl(Me.txt2ndLanguage.Text)
        Catch ex As FormatException
            MsgBox("The value you entered for the 2nd Language course is not valid")
            Me.txtEnglish.Focus()
        End Try

        Try
            geography = CDbl(Me.txtGeography.Text)
        Catch ex As FormatException
            MsgBox("The value you entered for the Geography course is not valid")
            Me.txtEnglish.Focus()
        End Try

        Try
            arts = CDbl(Me.txtArts.Text)
        Catch ex As FormatException
            MsgBox("The value you entered for the Arts course is not valid")
            Me.txtEnglish.Focus()
        End Try

        Try
            math = CDbl(Me.txtMath.Text)
        Catch ex As FormatException
            MsgBox("The value you entered for the Math course is not valid")
            Me.txtEnglish.Focus()
        End Try

        Try
            science = CDbl(Me.txtScience.Text)
        Catch ex As FormatException
            MsgBox("The value you entered for the Science course is not valid")
            Me.txtEnglish.Focus()
        End Try

        Try
            physEduc = CDbl(Me.txtPhysEduc.Text)
        Catch ex As FormatException
            MsgBox("The value you entered for the Physical Education course is not valid")
            Me.txtEnglish.Focus()
        End Try

        ' Calculate the total and the average
        total = english + history + economics + language2 + _
              geography + arts + math + science + physEduc
        average = total / 9

        ' Display the total and the average
        Me.txtTotal.Text = total.ToString("F")
        Me.txtAverage.Text = average.ToString("F")
End Sub

Return to the form.
Double-click the Close button and implement its event as follows:

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

Execute the application to test it

Stream Writing

A streaming operation is typically used to create a stream. Once the stream is ready, you can write data to it. The writing operation is performed through various classes. One of these classes is BinaryWriter.

The BinaryWriter class can be used to write values of primitive data types (char, int, float, double, etc). To use a BinaryWriter value, you can first declare its pointer. To do this, you would use one of the class' three constructors. The first constructor is the default, meaning it doesn't take an argument. The second constructor has the following syntax:

Public Sub New(ByVal output As Stream)

This constructor takes as argument a Stream value, which could be a FileStream variable. Here is an example:

Private Sub btnStart_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnStart.Click
        Dim fileName As String = "Persons.spr"

        Dim fstPersons As FileStream = New FileStream(fileName, FileMode.Create)
        Dim wrtPersons As BinaryWriter = New BinaryWriter(fstPersons)
End Sub

Most classes that are used to add values to a stream are equipped with a method called Write. This is also the case for the BinaryWriter class. This method takes as argument the value that must be written to the stream. The method is overloaded so that there is a version for each primitive data type. Here is an example that adds strings to a newly created file:

Private Sub btnStart_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnStart.Click
        Dim fileName As String = "Persons.spr"

        Dim fstPersons As FileStream = New FileStream(fileName, FileMode.Create)
        Dim wrtPersons As BinaryWriter = New BinaryWriter(fstPersons)

        wrtPersons.Write("James Bloch")
        wrtPersons.Write("Catherina Wallace")
        wrtPersons.Write("Bruce Lamont")
        wrtPersons.Write("Douglas Truth")
End Sub

Stream Closing

When you use a stream, it requests resources from the operating system and uses them while the stream is available. When you are not using the stream anymore, you should free the resources and make them available again to the operating system so that other services can use them. This is done by closing the stream.

To close a stream, you can can call the Close() method of the class(es) you were using. Here are examples:

Private Sub btnStart_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnStart.Click
        Dim fileName As String = "Persons.spr"

        Dim fstPersons As FileStream = New FileStream(fileName, FileMode.Create)
        Dim wrtPersons As BinaryWriter = New BinaryWriter(fstPersons)

        wrtPersons.Write("James Bloch")
        wrtPersons.Write("Catherina Wallace")
        wrtPersons.Write("Bruce Lamont")
        wrtPersons.Write("Douglas Truth")

        wrtPersons.Close()
        fstPersons.Close()
End Sub

Practical Learning: Writing to a Stream

Right-click the form and click View Code
In the top section of the file, type Imports System.IO as the first line of the file
Display the form
In the Toolbox, click the SaveFileDialog button and click the form
In the Properties window, change the following properties
DefaultExt: ros
Filter: ROSH Students Grades (.ros)|.ros|All Files(.)|
Title: Save Student Grades As

On the form, double-click the Save button and implement its Click event as follows:

Private Sub btnSave_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) _
			Handles btnSave.Click
        Dim stmGrades As FileStream
        Dim bnwGrades As BinaryWriter

        ' The information will not be saved if there is no name for the student
        If Me.txtStudentName.Text = "" Then
            MsgBox("The report cannot be saved without the name of the student")
            Me.txtStudentName.Focus()
            Exit Sub
        End If

        ' The information will not be saved if there is no school year
        If Me.txtSchoolYear1.Text = "" Then
            MsgBox("The report cannot be saved without the school year")
            Me.txtSchoolYear1.Focus()
            Exit Sub
        End If

        If Me.txtSchoolYear2.Text = "" Then
            MsgBox("The report cannot be saved without the school year")
            Me.txtSchoolYear2.Focus()
            Exit Sub
        End If

        Dim strFilename As String

        strFilename = Me.txtStudentName.Text + Me.txtSchoolYear1.Text + Me.txtSchoolYear2.Text
        Me.saveFileDialog1.FileName = strFilename
        ' Display the Save dialog box
        ' Find out if the user clicked OK or pressed Enter
        If Me.saveFileDialog1.ShowDialog() = DialogResult.OK Then
            ' If the used provided a name that already exists for an existing file
            If File.Exists(Me.saveFileDialog1.FileName) Then
                ' Find out if the user wants to replace the existing file
                Dim answer As System.Windows.Forms.DialogResult = _
                        MessageBox.Show("The student report exists already." + _
                                        "Do you want to replace it?", _
                                        "Save Student Report", _
                                        MessageBoxButtons.YesNo)

                ' If the user wants to replace it
                If answer = DialogResult.Yes Then
                    stmGrades = New FileStream(Me.saveFileDialog1.FileName, FileMode.Create)
                    bnwGrades = New BinaryWriter(stmGrades)

                    ' Then overwrite it
                    bnwGrades.Write(Me.txtStudentName.Text)
                    bnwGrades.Write(Me.txtSchoolYear1.Text)
                    bnwGrades.Write(Me.txtSchoolYear2.Text)
                    bnwGrades.Write(CDbl(Me.txtEnglish.Text))
                    bnwGrades.Write(CDbl(Me.txtHistory.Text))
                    bnwGrades.Write(CDbl(Me.txtEconomics.Text))
                    bnwGrades.Write(CDbl(Me.txt2ndLanguage.Text))
                    bnwGrades.Write(CDbl(Me.txtGeography.Text))
                    bnwGrades.Write(CDbl(Me.txtArts.Text))
                    bnwGrades.Write(CDbl(Me.txtMath.Text))
                    bnwGrades.Write(CDbl(Me.txtScience.Text))
                    bnwGrades.Write(CDbl(Me.txtPhysEduc.Text))

                    bnwGrades.Close()
                    stmGrades.Close()
                Else
                    stmGrades = New FileStream(Me.saveFileDialog1.FileName, FileMode.Create)
                    bnwGrades = New BinaryWriter(stmGrades)

                    bnwGrades.Write(Me.txtStudentName.Text)
                    bnwGrades.Write(Me.txtSchoolYear1.Text)
                    bnwGrades.Write(Me.txtSchoolYear2.Text)
                    bnwGrades.Write(CDbl(Me.txtEnglish.Text))
                    bnwGrades.Write(CDbl(Me.txtHistory.Text))
                    bnwGrades.Write(CDbl(Me.txtEconomics.Text))
                    bnwGrades.Write(CDbl(Me.txt2ndLanguage.Text))
                    bnwGrades.Write(CDbl(Me.txtGeography.Text))
                    bnwGrades.Write(CDbl(Me.txtArts.Text))
                    bnwGrades.Write(CDbl(Me.txtMath.Text))
                    bnwGrades.Write(CDbl(Me.txtScience.Text))
                    bnwGrades.Write(CDbl(Me.txtPhysEduc.Text))

                    bnwGrades.Close()
                    stmGrades.Close()
                End If
            End If
        End If
    End Sub

Execute the application and create a record:
Save the record and close the form

Stream Reading

As opposed to writing to a stream, you may want to read existing data from it. Before doing this, you can first specify your intent to the streaming class using the FileMode enumerator. This can be done using the FileStream class as follows:

Private Sub btnStart_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnStart.Click
        Dim fileName As String = "Persons.spr"

        '        Dim fstPersons As FileStream = New FileStream(fileName, FileMode.Create)
        '       Dim wrtPersons As BinaryWriter = New BinaryWriter(fstPersons)

        '      wrtPersons.Write("James Bloch")
        '     wrtPersons.Write("Catherina Wallace")
        '    wrtPersons.Write("Bruce Lamont")
        '   wrtPersons.Write("Douglas Truth")
        '
        '     wrtPersons.Close()
        '    fstPersons.Close()

        Dim fstPersons As New FileStream(fileName, FileMode.Open)
End Sub

Once the stream is ready, you can get prepared to read data from it. To support this, you can use the BinaryReader class. This class provides two constructors. One of the constructors (the first) has the following syntax:

Public Sub New(ByVal input As Stream)

This constructor takes as argument a Stream value, which could be a FileStream object. After declaring a FileStream variable using this constructor, you can read data from it. To support this, the class provides an appropriate method for each primitive data type.

After using the stream, you should close it to reclaim the resources it was using. This is done by calling the Close() method.

Here is an example of using the mentioned methods:

Private Sub btnStart_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnStart.Click
        Dim fileName As String = "Persons.spr"

        '       Dim fstPersons As FileStream = New FileStream(fileName, FileMode.Create)
        '       Dim wrtPersons As BinaryWriter = New BinaryWriter(fstPersons)

        '      wrtPersons.Write("James Bloch")
        '      wrtPersons.Write("Catherina Wallace")
        '      wrtPersons.Write("Bruce Lamont")
        '      wrtPersons.Write("Douglas Truth")
        '
        '     wrtPersons.Close()
        '     fstPersons.Close()

        Dim fstPersons As New FileStream(fileName, FileMode.Open)
        Dim rdrPersons As New BinaryReader(fstPersons)

        rdrPersons.Close()
        fstPersons.Close()
End Sub

Practical Learning: Reading From a Stream

In the Toolbox, click the OpenFileDialog button and click the form
In the Properties window, change the following properties
DefaultExt: ros
Filter: ROSH Students Grades (.ros)|.ros|All Files(.)|
Title: Open Student Grades

On the form, double-click the Save button and implement its Click event as follows:

Private Sub btnOpen_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) _
			Handles btnOpen.Click
        ' Display the Open dialog box
        ' Find out if the user selected a file and clicked OK
        If Me.openFileDialog1.ShowDialog() = DialogResult.OK Then
            Dim stmGrades As New FileStream(Me.openFileDialog1.FileName, FileMode.Open)
            Dim bnrGrades As New BinaryReader(stmGrades)

            If File.Exists(Me.openFileDialog1.FileName) Then
                ' Retrieve the values from the file
                Me.txtStudentName.Text = bnrGrades.ReadString()
                Me.txtSchoolYear1.Text = bnrGrades.ReadString()
                Me.txtSchoolYear2.Text = bnrGrades.ReadString()
                Me.txtEnglish.Text = bnrGrades.ReadDouble().ToString("F")
                Me.txtHistory.Text = bnrGrades.ReadDouble().ToString("F")
                Me.txtEconomics.Text = bnrGrades.ReadDouble().ToString("F")
                Me.txt2ndLanguage.Text = bnrGrades.ReadDouble().ToString("F")
                Me.txtGeography.Text = bnrGrades.ReadDouble().ToString("F")
                Me.txtArts.Text = bnrGrades.ReadDouble().ToString("F")
                Me.txtMath.Text = bnrGrades.ReadDouble().ToString("F")
                Me.txtScience.Text = bnrGrades.ReadDouble().ToString("F")
                Me.txtPhysEduc.Text = bnrGrades.ReadDouble().ToString("F")

                ' Close the stream
                bnrGrades.Close()
                stmGrades.Close()

                ' Since we didn't save the results of the calculations,
                ' call the Calculate button to do it
                Me.btnCalculate_Click(sender, e)
            End If
        End If
End Sub

Execute the application and open the previously saved record


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