Microsoft Visual C# File Processing: Directories

• 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

1. Start Microsoft Visual C#
2. To create a new application, on the main menu, click File -> New Project...
3. In the middle list, click Windows Application
4. Set the name to WattsALoan2 and click OK
5. To be able to use the Visual Basic library, in the Solution Explorer, right-click WattsALoan2 and click Add Reference...
6. In the .NET property page, click Microsoft.VisualBasic
    
   
7. Click OK
8. Design the form as follows:
    

   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

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

   private void btnCalculate_Click(object sender, EventArgs e)
   {
       double LoanAmount     = 0.00,
              InterestRate   = 0.00,
              Periods        = 0.00,
              MonthlyPayment = 0.00;
   
       try {
   	 LoanAmount = double.Parse(txtLoanAmount.Text);
       }
       catch(FormatException)
       {
   	 MessageBox.Show("Invalid Loan Amount");
       }
   				 
       try {
   	 InterestRate = double.Parse(txtInterestRate.Text);
       }
       catch(FormatException)
       {
   	 MessageBox.Show("Invalid Interest Rate");
       }
   				 
       try {
   	 Periods = double.Parse(txtPeriods.Text);
       }
       catch(FormatException)
       {
   	 MessageBox.Show("Invalid Periods Value");
       }
   				 
       try {
   	 MonthlyPayment =
   	     Microsoft.VisualBasic.Financial.Pmt(
   			InterestRate/ 12 / 100,
   		        Periods,
   			-LoanAmount,
   			0 ,
   			Microsoft.VisualBasic.DueDate.BegOfPeriod);
   	 txtMonthlyPayment.Text = MonthlyPayment.ToString("F");
       }
       catch(FormatException)
       {
   	 MessageBox.Show("Invalid Periods Value");
       }
   }

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

    private void btnClose_Click(object sender, EventArgs e)
    {
        Close();
    }

11. Scroll up completely and, under the other using lines, type using System.IO;
12. To create a new form, on the main menu, click Project -> Add Windows Form...
13. In the middle list, make sure Windows Form is selected.
    Set the Name to NewEmployee and click Add
14. Design the form as follows:
     

    Control Text Name Label Employee #: TextBox txtEmployeeNumber Label Employee Name: TextBox txtEmployeeName Button Create btnCreate Button Close btnClose

15. Double-click the Close button
16. Implement the event as follows:
    

    using System;
    using System.Collections.Generic;
    using System.ComponentModel;
    using System.Data;
    using System.Drawing;
    using System.Linq;
    using System.Text;
    using System.Windows.Forms;
    using System.IO;
    
    namespace WattsALoan2
    {
        public partial class NewEmployee : Form
        {
            public NewEmployee()
            {
                InitializeComponent();
            }
    
            private void btnClose_Click(object sender, EventArgs e)
            {
                Close();
            }
        }
    }

17. Access the first form
18. Double-click the New button and implement the event as follows:
    

    private void btnNewEmployee_Click(object sender, EventArgs e)
    {
        NewEmployee frmNewEmployee = new NewEmployee();
    
        frmNewEmployee.ShowDialog();
    }

19. Return to the form

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 static DirectoryInfo CreateDirectry(string path);

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 directory 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 d until the end of the specified path

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

1. On the (main) form, double-click an unoccupied area of its body
2. Implement its Load event as follows:
   

   private void Form1_Load(object sender, EventArgs e)
   {
       string strDirectory = "C:\\Watts A Loan";
   
       if (!Directory.Exists(strDirectory))
           Directory.CreateDirectory(strDirectory);
   
       string strFilename = strDirectory + "\\Employees.wal";
   
       FileInfo fiEmployees = new FileInfo(strFilename);
   
       // If the employees file was not created already,
       // then create it
       if (!fiEmployees.Exists)
       {
           StreamWriter stwEmployees = fiEmployees.CreateText();
   
           // And create a John Doe employee
           try
           {
               stwEmployees.WriteLine("00-000");
               stwEmployees.WriteLine("John Doe");
           }
           finally
           {
               stwEmployees.Close();
           }
       }
   }

3. Display the NewEmployee form and double-click its Create button
4. Implement its Click event as follows:
   

   private void btnCreate_Click(object sender, EventArgs e)
   {
       string strFilename = "C:\\Watts A Loan\\Employees.wal";
       FileInfo fiEmployees = new FileInfo(strFilename);
       StreamWriter stwEmployees = null;
   
       // Normally, we should have the file already but just in case...
       if (!fiEmployees.Exists)
           stwEmployees = fiEmployees.CreateText();
       else // If the file exists already, then we will only add to it
           stwEmployees = fiEmployees.AppendText();
   
       try
       {
           stwEmployees.WriteLine(txtEmployeeNumber.Text);
           stwEmployees.WriteLine(txtEmployeeName.Text);
       }
       finally
       {
           stwEmployees.Close();
       }
   
       txtEmployeeNumber.Text = "";
       txtEmployeeName.Text = "";
       txtEmployeeNumber.Focus();
   }

5. Return to the (main) form

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 static bool Exists(String path);

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.

To get rid of a directory, you can call the Delete() method of the Directory class. It is overloaded with two versions. One of the versions uses the following syntax;

public static void Delete(string path);

When calling this method, pass the complete path as argument. The other version uses the following syntax:

public static void Delete(string path, bool recursive);

This time, the second argument allows you to specifies whether you want the sub-folders and their contents to be deleted also.

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.

1. In the combo box on top of the Properties window, select txtAccountNumber
2. In the Events section, double-click Leave and implement the event as follows:
   

   private void txtAccountNumber_Leave(object sender, EventArgs e)
   {
       string strPath = "C:\\Watts A Loan";
   
       DirectoryInfo diLoans =
            new DirectoryInfo(strPath);
       FileInfo[] aryLoans = diLoans.GetFiles("*",
   		SearchOption.AllDirectories);
   
       string strFilename = txtAccountNumber.Text + ".wal";
       string strFullname = strPath + "none.wal";
       bool found = false;
   
       foreach(FileInfo fle in aryLoans)
       {
           if( fle.Name == strFilename )
           {
               found = true;
               strFullname = fle.FullName;
           }
       }
   
       if( found == true )
       {
           FileStream stmLoans = File.Open(strFullname,
                                 FileMode.Open,
                                 FileAccess.Read);
           BinaryReader bnrLoans = new BinaryReader(stmLoans);
   
           txtAccountNumber.Text = bnrLoans.ReadString();
           txtCustomerName.Text = bnrLoans.ReadString();
           txtEmployeeNumber.Text = bnrLoans.ReadString();
           txtEmployeeName.Text = bnrLoans.ReadString();
           txtLoanAmount.Text = bnrLoans.ReadString();
           txtInterestRate.Text = bnrLoans.ReadString();
           txtPeriods.Text = bnrLoans.ReadString();
           txtMonthlyPayment.Text = bnrLoans.ReadString();
   
           bnrLoans.Close();
           stmLoans.Close();
       }
   }

3. In the combo box on top of the Properties window, select txtEmployeeNumber
4. On the Properties window, click the Events button and double-click Leave
5. Implement the event as follows:
   

   private void txtEmployeeNumber_Leave(object sender, EventArgs e)
   {
       string strFilename = "C:\\Watts A Loan\\Employees.wal";
       FileInfo fiEmployees = new FileInfo(strFilename);
   
       if (fiEmployees.Exists)
       {
           if (txtEmployeeNumber.Text == "")
           {
               txtEmployeeName.Text = "";
               return;
           }
           else
           {
               StreamReader strEmployees = fiEmployees.OpenText();
               string strEmployeeNumber, strEmployeeName;
               bool found = false;
   
               try
               {
                   using (strEmployees = new StreamReader(strFilename))
                   {
                       while (strEmployees.Peek() >= 0)
                       {
                           strEmployeeNumber = strEmployees.ReadLine();
   
                           if (strEmployeeNumber == txtEmployeeNumber.Text)
                           {
                               strEmployeeName = strEmployees.ReadLine();
                               txtEmployeeName.Text = strEmployeeName;
                               found = true;
                           }
                       }
                   }
                   // When the application has finished checking the file
                   // if there was no employee with that number, let the user know
                   if (found == false)
                   {
                       MessageBox.Show("No employee with that number was found");
                       txtEmployeeName.Text = "";
                       txtEmployeeNumber.Focus();
                   }
               }
               finally
               {
                   strEmployees.Close();
               }
           }
       }
   }

6. Return to the form and double-click the Save button
7. Implement the event as follows:
   

   private void btnSave_Click(object sender, EventArgs e)
   {
       string strPath = "C:\\Watts A Loan\\" + txtAccountNumber.Text + ".wal";
   
       FileStream stmLoan = File.Create(strPath);
       BinaryWriter bnwLoan = new BinaryWriter(stmLoan);
   
       bnwLoan.Write(txtAccountNumber.Text);
       bnwLoan.Write(txtCustomerName.Text);
       bnwLoan.Write(txtEmployeeNumber.Text);
       bnwLoan.Write(txtEmployeeName.Text);
       bnwLoan.Write(txtLoanAmount.Text);
       bnwLoan.Write(txtInterestRate.Text);
       bnwLoan.Write(txtPeriods.Text);
       bnwLoan.Write(txtMonthlyPayment.Text);
   
       txtAccountNumber.Text = "";
       txtCustomerName.Text = "";
       txtEmployeeNumber.Text = "";
       txtEmployeeName.Text = "";
       txtLoanAmount.Text = "";
       txtInterestRate.Text = "";
       txtPeriods.Text = "";
       txtMonthlyPayment.Text = "";
   
       txtAccountNumber.Focus();
   
       bnwLoan.Close();
       stmLoan.Close();
   }

8. Execute the application to test it
9. 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

10. Process a few loans
     
11. Close the application