Visual C# File Processing: Operations on Files

	File Information: Operations on Files

Opening a File

As opposed to creating a file, probably the second most regular operation performed on a file consists of opening it to read or explore its contents. To support opening a file, the FileInfo class is equipped with the Open() method that is overloaded with three versions.

If you have a text-based file and want to directly read from it, you can use the StreamReader class that is equipped with Read() and ReadLine() methods. As done for the StreamWriter class, after using a StreamReader object, make sure you close it.

Here is an example:

Private Sub btnOpen_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) _
			Handles btnOpen.Click
        Dim rdrMembers As StreamReader = New StreamReader("People.txt")
        txtFirstName.Text = rdrMembers.ReadLine()
        txtLastName.Text = rdrMembers.ReadLine()
        txtHomePhone.Text = rdrMembers.ReadLine()
        txtEmailAddress.Text = rdrMembers.ReadLine()
        rdrMembers.Close()
End Sub

Practical Learning: Opening a File

Access the module of the first form.
In the top section of the file, create a class named CEmployee as follows:

Imports System.IO

Public Class CEmployee
    Public EmployeeNumber As String
    Public FullName As String
End Class

In the Class Name combo box, select txtEmployeeNumber
In the Method Name combo box, select Leave

Implement the new event as follows:

Private Sub txtEmployeeNumber_Leave(ByVal sender As Object, ByVal e As System.EventArgs) _
		Handles txtEmployeeNumber.Leave
        ' Create a FileInfo object based on the file that contains the employees
        Dim fleEmployees As FileInfo = New FileInfo("Employees.txt")
        ' Open the file
        Dim stmEmployees As StreamReader = fleEmployees.OpenText()
        ' We will need to create a list of employees from the file
        Dim lstEmployees As ArrayList = New ArrayList

        ' Use exception handling just in case
        Try
            ' This String variable will hold a line of text
            Dim strData As String = Nothing

            ' "Scan" the file, reading each line
            Do
                strData = stmEmployees.ReadLine()

                ' We will need to locate each employee
                Dim empl As CEmployee = New CEmployee
                ' Get the current line of text as the employee number
                ' and store its value in the first member of the local class
                empl.EmployeeNumber = strData
                ' Store the next line of text as employee name
                ' in the second member variable of the CEmployee object
                empl.FullName = stmEmployees.ReadLine()
                ' Now, store the CEmployee object as an item of the list
                lstEmployees.Add(empl)
            Loop Until strData = Nothing
        Finally
            stmEmployees.Close()
        End Try

        ' After creating a list of employees based on the file,
        ' "scan" the list to locate each employee
        Dim i As Integer
        For i = 0 To lstEmployees.Count - 1
            ' Retrieve each CEmployee object
            Dim empl As CEmployee = lstEmployees(i)
            ' If you find an employee number that corresponds to the value
            ' in the Prepared By text box, retrieve its corresponding
            ' employee name and display it in the next text box
            If empl.EmployeeNumber = txtEmployeeNumber.Text Then
                txtEmployeeName.Text = empl.FullName
            End If
        Next
End Sub

Display the form.
In the Toolbox, click the SaveFileDialog button and click the form
In the Properties window, change its characteristics as follows:
DefaultExt: txt
Filter: Loan Preparation (*.txt)|*.txt|All Files(*.*)|
Title: Save Loan Preparation As
In the Toolbox, click the OpenFileDialog button and click the form
In the Properties window, change its characteristics as follows:
DefaultExt: txt
Filter: Loan Preparation (*.txt)|*.txt|All Files(*.*)|
Title: Open Existing Loan Preparation
Save all
Right-click the form and click View Code
In the top section of the file, import the System.IO namespace:
Imports System.IO Public Class Form1
In the Class Name combo box, select mnuFileSame

In the Method Name combo box, select Click and implement the event as follows:

Private Sub mnuFileSave_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) _
			Handles mnuFileSave.Click
        If txtEmployeeNumber.Text = "" Or txtEmployeeNumber.Text = "00-000" Then
            MsgBox("You must enter the employee number of the clerk " & _
              "who prepared the loan")
            txtEmployeeNumber.Text = "00-000"
            txtEmployeeNumber.Focus()
            Exit Sub
        End If

        If txtFullName.Text = "" Then
            MsgBox("You must enter the name of the customer whose loan " & _
              "was prepared")
            txtFullName.Focus()
            Exit Sub
        End If

        If txtLoanAmount.Text = "" Or txtLoanAmount.Text = "0.00" Then
            MsgBox("Invalid Loan Amount")
            txtLoanAmount.Focus()
            Exit Sub
        End If

        If txtInterestRate.Text = "" Then
            MsgBox("Invalid Interest Rate")
            txtInterestRate.Focus()
            Exit Sub
        End If

        If txtPeriods.Text = "" Then
            MsgBox("Invalid number of period")
            txtPeriods.Focus()
            Exit Sub
        End If

        CalculateLoan()

        If saveFileDialog1.ShowDialog() = DialogResult.OK Then
            Dim fleLoan As FileInfo = New FileInfo(saveFileDialog1.FileName)
            Dim swrLoan As StreamWriter = fleLoan.CreateText()

            Try
                swrLoan.WriteLine(txtEmployeeNumber.Text)
                swrLoan.WriteLine(txtEmployeeName.Text)
                swrLoan.WriteLine(txtFullName.Text)
                swrLoan.WriteLine(txtEmployerName.Text)
                swrLoan.WriteLine(txtHomePhone.Text)
                swrLoan.WriteLine(txtWorkPhone.Text)
                swrLoan.WriteLine(txtLoanAmount.Text)
                swrLoan.WriteLine(txtInterestRate.Text)
                swrLoan.WriteLine(txtPeriods.Text)
                swrLoan.WriteLine(txtPayment.Text)

                txtEmployeeNumber.Text = "00-000"
                txtEmployeeName.Text = ""
                txtFullName.Text = ""
                txtEmployerName.Text = ""
                txtHomePhone.Text = ""
                txtWorkPhone.Text = ""
                txtLoanAmount.Text = "0.00"
                txtInterestRate.Text = "8.25"
                txtPeriods.Text = "60"
                txtPayment.Text = "0.00"

                txtEmployeeNumber.Focus()
            Finally
                swrLoan.Flush()
                swrLoan.Close()
            End Try
        End If
 End Sub

In the Class Name combo box, select mnuFileOpen

In the Method Name combo box, select Click and implement the event as follows:

Private Sub mnuFileOpen_Click(ByVal sender As Object, ByVal e As System.EventArgs) _
			Handles mnuFileOpen.Click
        If openFileDialog1.ShowDialog() = DialogResult.OK Then
            ' Create a FileInfo object based on the file
            Dim fleLoan As FileInfo = New FileInfo(openFileDialog1.FileName)
            ' Open the file
            Dim stmLoan As StreamReader = fleLoan.OpenText()

            ' Use exception handling just in case
            Try
                txtEmployeeNumber.Text = stmLoan.ReadLine()
                txtEmployeeName.Text = stmLoan.ReadLine()
                txtFullName.Text = stmLoan.ReadLine()
                txtEmployerName.Text = stmLoan.ReadLine()
                txtHomePhone.Text = stmLoan.ReadLine()
                txtWorkPhone.Text = stmLoan.ReadLine()
                txtLoanAmount.Text = stmLoan.ReadLine()
                txtInterestRate.Text = stmLoan.ReadLine()
                txtPeriods.Text = stmLoan.ReadLine()
                txtPayment.Text = stmLoan.ReadLine()
            Finally
                stmLoan.Close()
            End Try
        End If
End Sub

Execute the application

Deleting a File

If you have an existing file you don't need anymore, you can delete it. This operation can be performed by calling the FileInfo.Delete() method. Its syntax is:

Overrides Public Sub Delete()

Here is an example:

Private Sub btnDelete_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnDelete.Click
        Dim fleMembers As FileInfo = New FileInfo("First.txt")
        fleMembers.Delete()
End Sub

Copying a File

You can make a copy of a file from one directory to another. To do this, you can call the FileInfo.CopyTo() method that is overloaded with two versions. The first version has the following syntax:

Overloads Public Function CopyTo(ByVal destFileName As String) As FileInfo

When calling this method, specify the path or directory that will be the destination of the copied file. Here is an example:

Private Sub btnCopy_Click(ByVal sender As Object, ByVal e As System.EventArgs) Handles btnCopy.Click
        Dim fleMembers As FileInfo = New FileInfo("People.txt")
        Dim strMyDocuments As String = Environment.GetFolderPath(Environment.SpecialFolder.Personal)
        fleMembers.CopyTo(strMyDocuments & "\Persons.txt")
End Sub

In this example, a file named Reality.txt in the directory of the project would be retrieved and its content would be applied to a new file named Federal.txt created in the My Documents folder of the local computer.

When calling the first version of the FileInfo.CopyTo() method, if the file exists already, the operation would not continue and you would simply receive a message box. If you insist, you can overwrite the target file. To do this, you can use the second version of this method. Its syntax is:

Overloads Public Function CopyTo(ByVal destFileName As String, _
   			      ByVal overwrite As Boolean) As FileInfo

The first argument is the same as that of the first version of the method. The second argument specifies what action to take if the file exists already in the target directory. If you want to overwrite it, pass the argument as true; otherwise, pass it as false.

Moving a File

If you copy a file from one directory to another, you would have two copies of the same file or the same contents in two files. Instead of copying, if you want, you can simply move the file from one directory to another. This operation can be performed by calling the FileInfo.MoveTo() method. Its syntax is:

Public Sub MoveTo(ByVal destFileName As String)

The argument to this method is the same as that of the CopyTo() method. After executing this method, the FileInfo object would be moved to the destFileName path.

Here is an example:

Private Sub btnMove_Click(ByVal sender As Object, ByVal e As System.EventArgs) Handles btnMove.Click
        Dim fleMembers As FileInfo = New FileInfo("Persons.txt")
        Dim strMyDocuments As String = Environment.GetFolderPath(Environment.SpecialFolder.Personal)
        fleMembers.CopyTo(strMyDocuments & "\peeps.txt")
End Sub


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