.NET File Processing: File Information

	File Information

Introduction

In its high level of support for file processing, the .NET Framework provides the FileInfo class. 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 Learning: Introducing File Information

To start a new application, on the main menu, click File -> New -> Project
In the Templates list, click Windows Forms Application
Set the name to WattsALoan1
In the Properties window, change the form's Text to Watts A Loan
To be able to use the Visual Basic library, in the Solution Explorer, right-click WattsALoan1 and click References...
Click Add New Reference...
In the .NET property page, click Microsoft.VisualBasic
Click OK and OK
In the Common Controls section of the Toolbox, click ToolTip and click the form

Design the form as follows:

Control	Name	Text	ToolTip on toolTip1
Label		Acnt #:
Label		Customer Name:
Label		Customer:
TextBox	txtAccountNumber		Account number of the customer requesting the loan
TextBox	txtCustomerName		Name of the customer requesting the loan
Label		Empl #:
Label		Employee Name:
Label		Prepared By:
TextBox	txtEmployeeNumber		Employee number of the clerk preparing the loan
TextBox	txtEmployeeName		Name of the clerk preparing the loan
Button	btnNewEmployee		Used to add a new employee to the company
Label		Loan Amount:
TextBox	txtLoanAmount		Amount of loan the customer is requesting
Label		Interest Rate:
TextBox	txtInterestRate		Annual percentage rate of the loan
Label		%
Label		Periods
TextBox		txtPeriods	The number of months the loan is supposed to last
Button	btnCalculate	Calculate	Used to calculate the monthly payment
Label		Monthly Payment:
TextBox	txtMonthlyPayment		The minimum amount the customer should pay every month
Button	btnClose	Close	Used to close the form

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

System::Void btnCalculate_Click(System::Object^  sender, 
				System::EventArgs^  e)
{
    double LoanAmount, InterestRate, Periods, MonthlyPayment;

    try {
	 LoanAmount = double::Parse(txtLoanAmount->Text);
    }
    catch(FormatException ^)
    {
	 MessageBox::Show(L"Invalid Loan Amount");
    }
				 
    try {
	 InterestRate = double::Parse(txtInterestRate->Text);
    }
    catch(FormatException ^)
    {
	 MessageBox::Show(L"Invalid Interest Rate");
    }
				 
    try {
	 Periods = double::Parse(txtPeriods->Text);
    }
    catch(FormatException ^)
    {
	 MessageBox::Show(L"Invalid Periods Value");
    }
				 
    try {
	 MonthlyPayment =
	     Microsoft::VisualBasic::Financial::Pmt(
				InterestRate / 12 / 100,
		                Periods,
				-LoanAmount,
				0 ,
			Microsoft::VisualBasic::DueDate::BegOfPeriod);
	 txtMonthlyPayment->Text = MonthlyPayment.ToString(L"C");
    }
    catch(FormatException ^)
    {
	 MessageBox::Show(L"Invalid Periods Value");
    }
}

Return to the form and double-click the Close button to implement its event as follows:
System::Void btnClose_Click(System::Object^ sender, System::EventArgs^ e) { Close(); }
Return to the form

File Initialization

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:

FileInfo ^ fleMembers = gcnew FileInfo(L"First.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 Learning: Initializing a File

Double-click an unoccupied area on the body form
Scroll up completely and, under the other using lines, type using namespace System::IO

Scroll down complement and change the Load event of the form as follows:

System::Void Form1_Load(System::Object^  sender, System::EventArgs^  e)
{
	 String ^ strFilename = L"Employees.wal";
	 FileInfo ^ fiEmployees = gcnew FileInfo(strFilename);
}

Save the file

File Creation

The FileInfo constructor is mostly meant only to indicate that you want to use a file, whether it exists already or it would be created. Based on this, if you execute an application that has only a FileInfo object created using the constructor as done above, nothing would happen.

To create a file, you have various alternatives. If you want to create one without writing anything in it, which implies creating an empty file, you can call the FileInfo::Create() method. Its syntax is:

public:
    FileStream ^ Create();

This method simply creates an empty file. Here is an example of calling it:

FileInfo ^ fleMembers = gcnew FileInfo(L"First.txt");
fleMembers->Create();

The FileInfo::Create() method returns a FileStream object. You can use this returned value to write any type of value into the file, including text. If you want to create a file that contains text, an alternative is to call the FileInfo::CreateText() method. Its syntax is:

public:
    StreamWriter CreateText();

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

File Existence

When you call the FileInfo::Create() or the FileInfo::CreateText() method, if the file passed as argument, or as the file in the path of the argument, exists already, it would be deleted and a new one would be created with the same name. This can cause the right file to be deleted. Therefore, before creating a file, you may need to check whether it exists already. To do this, you can check the value of the Boolean FileInfo::Exists property. This property holds a true value if the file exists already and it holds a false value if the file doesn't exist or it doesn't exist in the path.

Here is an example of checking the existence of a file:

FileInfo ^ fleMembers = gcnew FileInfo(L"First.txt");
fleMembers->Create();

if( fleMembers.Exists == true )
	return;

Practical Learning: Creating a Text File

Change the Load event of the form as follows:

System::Void Form1_Load(System::Object^  sender, System::EventArgs^  e)
{
    String ^ strFilename = L"Employees.wal";
    FileInfo ^ fiEmployees = gcnew FileInfo(strFilename);

    // If the employees file was not created already,
    // then create it
    if( !fiEmployees->Exists )
    {
	 StreamWriter ^ stwEmployees = fiEmployees->CreateText();
    }
}

Save the file

Writing to a File

As mentioned earlier, the FileInfo::Create() method returns a FileStream object. You can use this to specify the type of operation that would be allowed on the 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).

Practical Learning: Writing to a Text File

Change the Load event of the form as follows:

System::Void Form1_Load(System::Object^  sender, System::EventArgs^  e)
{
	 String ^ strFilename = L"Employees.wal";
	 FileInfo ^ fiEmployees = gcnew 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(L"00-000");
		 stwEmployees->WriteLine(L"John Doe");
	    }
	    finally
	    {
		 stwEmployees->Close();
	    }
	 }
}

Save the file

Appending 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 Learning: Writing to a Text File

To create a new form, on the main menu, click Project -> Add New Item...
In the Templates list, click Windows Form
Set the Name to NewEmployee and click Add

Design the form as follows:

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

Right-click the form and click View Code
In the top section of the file, under the using using lines, type
using namespace System::IO;
Return to the New Employee form and double-click the Create button

Implement its event as follows:

System::Void btnCreate_Click(System::Object^  sender, System::EventArgs^  e)
{
	 String ^ strFilename = L"Employees.wal";
	 FileInfo ^ fiEmployees = gcnew FileInfo(strFilename);
	 StreamWriter ^ stwEmployees = nullptr;

	 // 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 = L"";
	 txtEmployeeName->Text = L"";
	 txtEmployeeNumber->Focus();
}

Return to the New Employee form and double-click the Close button

Implement its event as follows:

System::Void btnClose_Click(System::Object^  sender, System::EventArgs^  e)
{
	 Close();
}

Access the Form1 form
Double-click the top New button
In the top section of the file, under the #pragma once line, type

#include "NewEmployee.h"

Scroll down and implement its Click event as follows:

System::Void btnNewEmployee_Click(System::Object^  sender, 
				System::EventArgs^  e)
{
    NewEmployee ^ frmNewEmployee = gcnew NewEmployee;

    frmNewEmployee->ShowDialog();
}

Return to the form
In the combo box on top of the Properties window, select txtEmployeeNumber
On the Properties window, click the Events button and double-click Leave

Implement the event as follows:

System::Void txtEmployeeNumber_Leave(System::Object^  sender, 
					System::EventArgs^  e) 
{
    String ^ strFilename = L"Employees.wal";
    FileInfo ^ fiEmployees = gcnew FileInfo(strFilename);

    if(fiEmployees->Exists )
    {
	 if( txtEmployeeNumber->Text == L"" )
	 {
		 txtEmployeeName->Text = L"";
		 return;
	 }
	 else
	 {
	     StreamReader ^ strEmployees = fiEmployees->OpenText();
	     String ^ strEmployeeNumber, ^ strEmployeeName;
	     bool found = false;

	     try {
		  while( 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(L"No employee with that number was found");
				 txtEmployeeName->Text = L"";
				 txtEmployeeNumber->Focus();
		  }
	    }
	    finally
	    {
		 strEmployees->Close();
	    }
	}
    }
}

Execute the application to test it

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

Process a loan
Close the application


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