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Directories

 

Introduction

A directory is a section of a medium (floppy disc, flash drive, hard drive, CD, DVD, etc) used to delimit a group of files. Because it is a "physical" area, it can handle operations not available on files. In fact, there are many fundamental differences between both:

  • A file is used to contain data. A directory doesn't contain data
  • A directory can contain one or more files and not vice-versa
  • A directory can contain other directories
  • A file can be moved from one directory to another. This operation is not possible vice-versa since a file cannot contain a directory

The similarities of both types are:

  • A directory or a file can be created. One of the restrictions is that two files cannot have the same name inside of the same directory. Two directories cannot have the same name inside of the same parent directory.
  • A directory or a file can be renamed. If a directory is renamed, the "path" of its file(s) changes
  • A directory or a file can be deleted. If a directory is deleted, its files are deleted also
  • A directory or a file can be moved. If a directory moves, it "carries" all of its files to the new location
  • A directory or a file can be copied. A file can be copied from one directory to another. If a directory is copied to a new location, all of its files are also copied to the new location

Practical LearningPractical Learning: Introducing Directories

  1. Create a new Windows Application, named WattsALoan2
  2. In the Solution Explorer, right-click Form1.vb and click Rename
  3. Type WattsALoan.vb and press Enter
  4. Design the form as follows:
     
    Watts' A Loan
    Control Name Text
    Label   If this is a new loan, enter a new account number and the name of the customer who is requesting the loan
    Label   To open a previously prepared loan, enter its account number and press Tab
    Label   Acnt #:
    Label   Customer Name:
    Label   Customer:
    TextBox txtAccountNumber  
    TextBox txtCustomerName  
    Label   Empl #:
    Label   Employee Name:
    Label   Prepared By:
    TextBox txtEmployeeNumber  
    TextBox txtEmployeeName  
    Button btnNewEmployee  
    Button btnNewCustomer  
    Label   Loan Amount:
    TextBox txtLoanAmount  
    Label   Interest Rate:
    TextBox txtInterestRate  
    Label   %
    Label   Periods
    TextBox   txtPeriods
    Button btnCalculate Calculate
    Label   Monthly Payment:
    TextBox txtMonthlyPayment  
    Button btnClose Close
  5. Double-click the Calculate button and implement its event as follows:
     
    Imports System.IO
    
    Public Class WattsALoan
    
        Private Sub btnCalculate_Click(ByVal sender As System.Object, _
                                       ByVal e As System.EventArgs) _
                                       Handles btnCalculate.Click
            Dim LoanAmount As Double
            Dim InterestRate As Double
            Dim Periods As Double
            Dim MonthlyPayment As Double
    
            Try
                LoanAmount = CDbl(txtLoanAmount.Text)
            Catch ex As Exception
                MsgBox("Invalid Loan Amount")
            End Try
    
            Try
                InterestRate = CDbl(txtInterestRate.Text)
            Catch ex As Exception
    
                MsgBox("Invalid Interest Rate")
            End Try
    
            Try
                Periods = CDbl(txtPeriods.Text)
            Catch ex As Exception
                MsgBox("Invalid Periods Value")
            End Try
    
            MonthlyPayment = Pmt(InterestRate / 12 / 100, _
                                 Periods, -LoanAmount, 0, _
                                 DueDate.BegOfPeriod)
            txtMonthlyPayment.Text = FormatCurrency(MonthlyPayment)
        End Sub
    End Class
  6. In the Class Name combo box, select btnClose
  7. 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
  8. To create a new form, on the main menu, click Project -> Add Windows Form...
  9. In the Templates list, make sure Windows Form is selected.
    Set the Name to NewEmployee and click Add
  10. Design the form as follows:
     
    Control Text Name
    Label Employee #:
    TextBox txtEmployeeNumber
    Label Employee Name:
    TextBox txtEmployeeName
    Button Create btnCreate
    Button Close btnClose
  11. Double-click the Close button
  12. Implement the event as follows:
     
    Imports System.IO
    
    Public Class NewEmployee
    
        Private Sub btnClose_Click(ByVal sender As System.Object, _
                                   ByVal e As System.EventArgs) _
                                   Handles btnClose.Click
            Close()
        End Sub
    End Class
  13. In the Solution Explorer, right-click WattsALoan.vb and click View Code
  14. In the Class Name combo box, select btnNewEmployee
  15. In the Method Name combo box, select Click and implement the event as follows:
     
    Private Sub btnNewEmployee_Click(ByVal sender As Object, _
                                         ByVal e As System.EventArgs) _
                                         Handles btnNewEmployee.Click
            Dim FormEmployee As NewEmployee = New NewEmployee()
    
            FormEmployee.ShowDialog()
    End Sub
  16. Save the file

Directory Creation

Before using a directory, you must first have it. You can use an existing directory if the operating system or someone else had already created one. You can also create a new directory. Directories are created and managed by various classes but the fundamental class is called Directory. Directory is a static class. All of its methods are static, which means you will never need to declare an instance of the Directory class in order to use it.

Besides the Directory class, additional operations of folders and sub-folders can be performed using the DirectoryInfo class.

To create a directory, you can call the CreateDirectory() method of the Directory class. This method is available in two versions. One of the versions uses the following syntax:

Public Shared Function CreateDirectory(path As String) As DirectoryInfo

This method takes as argument the (complete) path of the desired directory. Here is an example:

E:\Programs\Business Orders\Customer Information

When this method is called:

  1. It first checks the parent drive, in this case E.
    If the drive doesn't exist, because this method cannot create a drive, the compiler would throw a DirectoryNotFoundException exception
  2. If the drive (in this case E) exists, the compiler moves to the first directory part of the path; in this case this would be the Programs folder in the E drive.
    If the folder doesn't exist, the compiler would create it. If that first director doesn't exist, this means that the other directory(ies), if any, under the first don't exist. So, the compiler would create it/them
  3. If the first directory exists and if there is no other directory under that directory, the compiler would stop and would not do anything further.
  4. If the directory exists and there is a sub-directory specified under it, the compiler would check the existence of that directory.
    If the sub-directory exists, the compiler would not do anything further and would stop.
    If the sub-directory doesn't exist, the compiler would create it
  5. The compiler would repeat step 4 until the end of the specified path

The Directory.CreateDirectory() method returns a DirectoryInfo object that you can use as you see fit.

Practical LearningPractical Learning: Creating a Directory

  1. In the Class Name combo box, select (WattsALoan Events)
  2. In the Method Name combo box, select Load and implement the event as follows:
     
    Private Sub WattsALoan_Load(ByVal sender As Object, _
                                    ByVal e As System.EventArgs) _
                                    Handles Me.Load
            Dim Folder As String
            Dim EmployeeWriter As StreamWriter
            Dim Filename As String = "Employees.wal"
            Dim EmployeeInformation As FileInfo = _
                    My.Computer.FileSystem.GetFileInfo(Filename)
    
            Folder = "C:\Watts A Loan"
    
            If Not Directory.Exists(Folder) Then
                Directory.CreateDirectory(Folder)
    
                Dim strFilename As String = Folder & "\Employees.wal"
    
                Dim fiEmployees As FileInfo = New FileInfo(strFilename)
    
                ' If the employees file was not created already,
                ' then create it
                If Not EmployeeInformation.Exists Then
                    EmployeeWriter = EmployeeInformation.CreateText()
    
                    ' And create a John Doe employee
                    Try
                        EmployeeWriter.WriteLine("00-000")
                        EmployeeWriter.WriteLine("John Doe")
                    Finally
                        EmployeeWriter.Close()
                    End Try
                End If
            End If
    End Sub
  3. In the Solution Explorer, right-click NewEmployee and click View Code
  4. In the Class Name combo box, select btnCreate
  5. In the Method Name combo box, select Click and implement the event as follows:
     
    Private Sub btnCreate_Click(ByVal sender As Object, _
                                    ByVal e As System.EventArgs) _
                                    Handles btnCreate.Click
            Dim Filename As String = "C:\Watts A Loan\Employees.wal"
            Dim EmployeeInformation As FileInfo
            Dim EmployeeWriter As StreamWriter
    
            EmployeeInformation = My.Computer.FileSystem.GetFileInfo(Filename)
    
            ' Normally, we should have the file already but just in case...
            If Not EmployeeInformation.Exists Then
                EmployeeWriter = EmployeeInformation.CreateText()
            Else ' If the file exists already, then we will only add to it
                EmployeeWriter = EmployeeInformation.AppendText()
            End If
    
            Try
                EmployeeWriter.WriteLine(txtEmployeeNumber.Text)
                EmployeeWriter.WriteLine(txtEmployeeName.Text)
            Finally
                EmployeeWriter.Close()
            End Try
    
            txtEmployeeNumber.Text = ""
            txtEmployeeName.Text = ""
            txtEmployeeNumber.Focus()
    End Sub
  6. Click the WattsALoan.vb [Design] tab

Checking for a Directory Existence

Before using or creating a directory, you can first check if it exists. This is because, if a directory already exists in the location where you want to create it, you would be prevented from creating one with the same name. In the same way, if you just decide to directly use a directory that doesn't exist, the operation you want to perform may fail because the directory would not be found.

To check whether a directory exists or not, you can call the Directory.Exists() Boolean static method. Its syntax is:

Public Shared Function Exists(path As String) As Boolean

This method receives the (complete) path of the directory. If the path exists, the method returns true. If the directory doesn't exist, the method returns false.

Locating a File

One of the most routine operations performed in a directory consists of looking for a file. Microsoft Windows operating systems and the user's intuition have different ways of addressing this issue. The .NET Framework also provides its own means of performing this operation, through various techniques. You can start by checking the sub-directories and files inside of a main directory.

To look for files in a directory, the DirectoryInfo class can assist you with its GetFiles() method, which is overloaded with three versions.

Practical LearningPractical Learning: Using Directories and Files

  1. In the Class Name combo box, select txtAccountNumber
  2. In the Method Name combo box, select Leave and implement the event as follows:
     
    Private Sub txtAccountNumber_Leave(ByVal sender As Object, _
                                           ByVal e As System.EventArgs) _
                                           Handles txtAccountNumber.Leave
            Dim Filename As String
            Dim LoanPath As String
            Dim FileFullname As String
            Dim ListOfLoans() As FileInfo
            Dim LoanReader As StreamReader
            Dim LoanFolder As DirectoryInfo
            Dim LoanInformation As FileInfo
            Dim Found As Boolean
    
            Found = False
            LoanPath = "C:\Watts A Loan"
    
            LoanFolder = New DirectoryInfo(LoanPath)
            ListOfLoans = LoanFolder.GetFiles("*", _
                                SearchOption.AllDirectories)
            Filename = txtAccountNumber.Text & ".wal"
            FileFullname = LoanPath & "none.wal"
    
            For Each fle As FileInfo In ListOfLoans
                If fle.Name = Filename Then
                    Found = True
                    FileFullname = fle.FullName
                End If
            Next
    
            If Found = True Then
    
                LoanInformation = My.Computer.FileSystem.GetFileInfo(Filename)
                LoanReader = LoanInformation.OpenText
                
                Try
                    txtAccountNumber.Text = LoanReader.ReadLine
                    txtCustomerName.Text = LoanReader.ReadLine
                    txtEmployeeNumber.Text = LoanReader.ReadLine
                    txtEmployeeName.Text = LoanReader.ReadLine
                    txtLoanAmount.Text = LoanReader.ReadLine
                    txtInterestRate.Text = LoanReader.ReadLine
                    txtPeriods.Text = LoanReader.ReadLine
                    txtMonthlyPayment.Text = LoanReader.ReadLine
                Finally
                    LoanReader.Close()
                End Try
            End If
    End Sub
  3. In the Class Name combo box, select txtEmployeeNumber
  4. In the Method Name combo box, select click Leave and implement the event as follows:
     
    Private Sub txtAccountNumber_Leave(ByVal sender As Object, _
                                           ByVal e As System.EventArgs) _
                                           Handles txtAccountNumber.Leave
            Dim Filename As String
            Dim LoanPath As String
            Dim FileFullname As String
            Dim ListOfLoans() As FileInfo
            Dim LoanReader As StreamReader
            Dim LoanFolder As DirectoryInfo
            Dim LoanInformation As FileInfo
            Dim Found As Boolean
    
            Found = False
            LoanPath = "C:\Watts A Loan"
    
            LoanFolder = New DirectoryInfo(LoanPath)
            ListOfLoans = LoanFolder.GetFiles("*", _
                                SearchOption.AllDirectories)
            Filename = txtAccountNumber.Text & ".wal"
            FileFullname = LoanPath & "none.wal"
    
            For Each fle As FileInfo In ListOfLoans
                If fle.Name = Filename Then
                    Found = True
                    FileFullname = fle.FullName
                End If
            Next
    
            If Found = True Then
    
                LoanInformation = My.Computer.FileSystem.GetFileInfo(FileFullname)
                MsgBox(LoanInformation.FullName)
                LoanReader = LoanInformation.OpenText
    
                Try
                    txtAccountNumber.Text = LoanReader.ReadLine
                    txtCustomerName.Text = LoanReader.ReadLine
                    txtEmployeeNumber.Text = LoanReader.ReadLine
                    txtEmployeeName.Text = LoanReader.ReadLine
                    txtLoanAmount.Text = LoanReader.ReadLine
                    txtInterestRate.Text = LoanReader.ReadLine
                    txtPeriods.Text = LoanReader.ReadLine
                    txtMonthlyPayment.Text = LoanReader.ReadLine
                Finally
                    LoanReader.Close()
                End Try
            End If
    End Sub
  5. In the Class Name combo box, select btn Save
  6. 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
            Dim LoanPath As String
            Dim LoanWriter As StreamWriter
    
            LoanPath = "C:\Watts A Loan\" & txtAccountNumber.Text & ".wal"
            LoanWriter = My.Computer.FileSystem.OpenTextFileWriter(LoanPath, False)
    
            Try
                LoanWriter.WriteLine(txtAccountNumber.Text)
                LoanWriter.WriteLine(txtCustomerName.Text)
                LoanWriter.WriteLine(txtEmployeeNumber.Text)
                LoanWriter.WriteLine(txtEmployeeName.Text)
                LoanWriter.WriteLine(txtLoanAmount.Text)
                LoanWriter.WriteLine(txtInterestRate.Text)
                LoanWriter.WriteLine(txtPeriods.Text)
                LoanWriter.WriteLine(txtMonthlyPayment.Text)
    
                txtAccountNumber.Text = ""
                txtCustomerName.Text = ""
                txtEmployeeNumber.Text = ""
                txtEmployeeName.Text = ""
                txtLoanAmount.Text = ""
                txtInterestRate.Text = ""
                txtPeriods.Text = ""
                txtMonthlyPayment.Text = ""
                txtAccountNumber.Focus()
            Finally
                LoanWriter.Close()
            End Try
    End Sub
  7. Execute the application to test it
  8. First create a few employees as follows:
     
    Employee # Employee Name
    42-806 Patricia Katts
    75-148 Helene Mukoko
    36-222 Frank Leandro
    42-808 Gertrude Monay
  9. Process a few loans
     
    Watts A Loan - Loan Preparation
     
    Watts A Loan - Loan Result
  10. Close the application
 

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