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Microsoft Visual C# File Processing: File Information

Introduction

In its high level of support for file processing, the .NET Framework provides a class named FileInfo. This class is equipped to handle all types of file-related operations including creating, copying, moving, renaming, or deleting a file. FileInfo is based on the FileSystemInfo class that provides information on characteristics of a file.

    

Practical LearningPractical Learning: Introducing File Information

  1. To start a new application, on the main menu, click File -> New Project
  2. In the middle list, click Windows Application
  3. Set the name to WattsALoan1
  4. In the Properties window, change the form's Text to Watts A Loan
  5. To be able to use the Visual Basic library, in the Solution Explorer, right-click WattsALoan1 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   Acnt #:
    Label   Customer Name:
    Label   Customer:
    TextBox txtAccountNumber  
    TextBox txtCustomerName  
    Label   Empl #:
    Label   Employee Name:
    Label   Prepared By:
    TextBox txtEmployeeNumber  
    TextBox txtEmployeeName  
    Button btnNewEmployee  
    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 = 0.00D,
           InterestRate = 0.00D,
           Periods = 0.00D,
           MonthlyPayment = 0.00D;

    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. Return to the form

Initializing File Information

The FileInfo class is equipped with one constructor whose syntax is: 

public FileInfo(String fileName);

This constructor takes as argument the name of a file or its complete path. If you provide only the name of the file, the compiler would consider the same directory of its project. Here is an example:

public partial class Exercise : Form
{
    private void btnSave_Click(object sender, EventArgs e)
    {
        FileInfo flePeople = new FileInfo("People.txt");
    }
}

Alternatively, if you want, you can provide any valid directory you have access to. In this case, you should provide the complete path.

Practical LearningPractical Learning: Initializing a File

  1. Double-click an unoccupied area on the body form
  2. Scroll up completely and, under the other using lines, type using System.IO;
  3. Scroll down complement and change the Load event of the form as follows: 
    private void Form1_Load(object sender, EventArgs e)
{
    string  strFilename = "Employees.wal";
    FileInfo  fiEmployees = new FileInfo(strFilename);
}

Writing Text to a File

After creating a file, you can write one or more values to it. An example of a value is text. If you want to create a file that contains text, the FileInfo class provides a method named CreateText . Its syntax is:

public StreamWriter CreateText();

This method returns a StreamWriter object. You can use this returned object to write text to the file.

Practical LearningPractical Learning: Creating a Text File

Writing a Value to a File

To write normal text to a file, you can first call the FileInfo.CreateText() method. This method returns a StreamWriter object. The StreamWriter class is based on the TextWriter class that is equipped with the Write() and the WriteLine() methods used to write values to a file. The Write() method writes text on a line and keeps the caret on the same line. The WriteLine() method writes a line of text and moves the caret to the next line.

After writing to a file, you should close the StreamWriter object to free the resources it was using during its operation(s). Here is an example:

private void btnSave_Click(object sender, EventArgs e)
{
    FileInfo flePeople = new FileInfo("People.txt");
    StreamWriter stwPeople = flePeople.CreateText();

    try
    {
        stwPeople.WriteLine(txtPerson1.Text);
        stwPeople.WriteLine(txtPerson2.Text);
        stwPeople.WriteLine(txtPerson3.Text);
        stwPeople.WriteLine(txtPerson4.Text);
    }
    finally
    {
        stwPeople.Close();

        txtPerson1.Text = "";
        txtPerson2.Text = "";
        txtPerson3.Text = "";
        txtPerson4.Text = "";
    }
}

Practical LearningPractical Learning: Writing to a Text File

Appending Text to a File

You may have created a text-based file and written to it. If you open such a file and find out that a piece of information is missing, you can add that information to the end of the file. To do this, you can call the FileInfo.AppenText() method. Its syntax is:

public StreamWriter AppendText();

When calling this method, you can retrieve the StreamWriter object that it returns, then use that object to add new information to the file.

Practical LearningPractical Learning: Writing to a Text File

  1. To create a new form, on the main menu, click Project -> Add Windows Form...
  2. In the middle list, make sure Windows Form is selected. Set the Name to NewEmployee and click Add

    3. Control Text Name
    Label Employee #:  
    TextBox   txtEmployeeNumber
    Label Employee Name:  
    TextBox   txtEmployeeName
    Button Create btnCreate
    Button Close btnClose
  3. Right-click the form and click View Code
  4. In the top section of the file, under the using using lines, type
    using System.IO;
  5. Return to the New Employee form and double-click the Create button
  6. Implement its event as follows:
    private void btnCreate_Click(object sender, EventArgs e)
{
    string  strFilename = "Employees.wal";
    FileInfo  fiEmployees = new FileInfo(strFilename);
    StreamWriter  stwEmployees = null;

    stwEmployees= fiEmployees.AppendText();
				 
    try {
	 stwEmployees.WriteLine(txtEmployeeNumber.Text);
	 stwEmployees.WriteLine(txtEmployeeName.Text);
    }
    finally
    {
	 stwEmployees.Close();
    }

    txtEmployeeNumber.Text = "";
    txtEmployeeName.Text = "";
    txtEmployeeNumber.Focus();
}
  7. Return to the New Employee form and double-click the Close button
  8. Implement its event as follows:
    private void btnClose_Click(object sender, EventArgs e)
{
    Close();
}
  9. Access the Form1 form
  10. Double-click the top New button and implement the event as follows:
    private void btnNewEmployee_Click(object sender, EventArgs e)
{
    NewEmployee  frmNewEmployee = new NewEmployee();

    frmNewEmployee.ShowDialog();
}
  11. Return to the form
  12. In the combo box on top of the Properties window, select txtEmployeeNumber
  13. On the Properties window, click the Events button and double-click Leave
  14. Implement the event as follows:
    private void txtEmployeeNumber_Leave(object sender, EventArgs e)
{
    string strFilename = "Employees.wal";
    FileInfo fiEmployees = new FileInfo(strFilename);

    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();
        }
    }
}
  15. Execute the application to test it
  16. 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
  17. Process a loan

    Watts A Loan

  18. Close the application

Reading from a File

As opposed to writing to a file, you can read from it. To support this, the FileInfo class is equipped with a method named OpenText(). Its syntax is:

public StreamReader OpenText();

This method returns a StreamReader object. You can then use this object to read the lines of a text file. Here is an example:

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;

namespace FileProcessing2
{
    public partial class Exercise : Form
    {
        public Exercise()
        {
            InitializeComponent();
        }

        private void btnSave_Click(object sender, EventArgs e)
        {
            FileInfo flePeople = new FileInfo("People.txt");
            StreamWriter stwPeople = flePeople.CreateText();

            try
            {
                stwPeople.WriteLine(txtPerson1.Text);
                stwPeople.WriteLine(txtPerson2.Text);
                stwPeople.WriteLine(txtPerson3.Text);
                stwPeople.WriteLine(txtPerson4.Text);
            }
            finally
            {
                stwPeople.Close();

                txtPerson1.Text = "";
                txtPerson2.Text = "";
                txtPerson3.Text = "";
                txtPerson4.Text = "";
            }
        }

        private void btnOpen_Click(object sender, EventArgs e)
        {
            string Filename = "People.txt";
            FileInfo flePeople = new FileInfo(Filename);
            StreamReader strPeople = flePeople.OpenText();

            try
            {
                txtPerson1.Text = strPeople.ReadLine();
                txtPerson2.Text = strPeople.ReadLine();
                txtPerson3.Text = strPeople.ReadLine();
                txtPerson4.Text = strPeople.ReadLine();
            }
            finally
            {
                strPeople.Close();
            }
        }
    }
}
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