1. CSCI 3327 Visual Basic Chapter 11: Files and Streams
UTPA – Fall 2011
Part of the slides is from Dr. John Abraham’s previous lecture slides. – Xiang Lian

2. Objectives In this chapter, you will
Learn how to use file processing to implement a business application
Get familiar with creating, writing to and reading from files
Know the sequential-access file processing
Use classes StreamWriter and StreamReader to write text to and read text from files

3. Data Hierarchy
Bits
Characters (ASCII or Unicode)
Fields
Records
File

4. Files and Streams File as a sequential stream of bytes
Each file ends with an End of File Marker
Windows keeps track of total number of bytes in a file
When a file is opened an object is created and a stream is associated with the object
Each program automatically gets 3 objects, console.out, console.in and console.error

5. File Processing Classes in .Net Framework
The System.IO namespace includes stream classes such as
StreamReader (for text input)
StreamWriter (for text output)
FileStream for both input and output to file
MemoryStream enables the transfer of data directly to and from memory
BufferedStream uses buffering to transfer data to and from a stream

6. Classes File and Directory
Files are organized in directories
Class directory provides capabilities for manipulating directories
File Class methods
AppendText, Copy, Create, CreateText, Delete, Exists, GetCreationTime, GetLastAccessTime, GetLastWriteTime, Move, Open, OpenRead, OpenText, OpenWrite
Show Program

7. Directory Class Methods
CreateDirectory
Delete
Exists
GetDirectories
GetFiles
GetCreationTime
GetLastAccessTime
GetLastWriteTime
Move

8. Create a File to Write Imports System.IO Declare two variables
Dim fileInfo As FileStream
Dim fileWriter As StreamWriter
Open File
fileInfo = New Filestream(filename, FileMode.Create, FileAccess.Write)
fileWriter = New StreamWriter(fileInfo)

9. Write to File
fileWriter.WriteLine(“text”)

10. Close File
Filewriter.Close()

11. Example 8.7: CreateAccounts.vb
URL:
Imports System.IO
Dim fileWriter As StreamWriter
Using fileChooser As New SaveFileDialog()
Result = fileChooser.ShowDialog()
fileName = fileChooser.FileName
End Using
Windows.Forms.DialogResult.Cancel
fileWriter = New StreamWriter(fileName, True)
fileWriter.WriteLine(“…”)
fileWriter.Close()
If the file does not exist, create a new file

12. Example 8.7: CreateAccounts.vb (cont'd)
Exceptions
Catch ex As IOException
Catch ex As FormatException

13. Struct Public Structure student Dim lastName As String
Dim firstName As String
Dim tele As String
Dim gpa As Decimal
End Structure
Public students As New List(Of student)
Public oneStudent As New student

14. Opening File Dim fileResult As DialogResult
OpenFileDialog1.ShowDialog()
If OpenFileDialog1.ShowDialog() = Windows.Forms.DialogResult.OK Then
fileName = OpenFileDialog1.FileName
txtFileName.Text = OpenFileDialog1.FileName
End If
If fileResult <> Windows.Forms.DialogResult.Cancel Then
Try
input = New FileStream(fileName, FileMode.Open, FileAccess.Read)
filereader = New StreamReader(input)
Catch ex As Exception
MessageBox.Show("Error Opening File", "Error Message", _
MessageBoxButtons.OK, MessageBoxIcon.Error)
End Try
btnReadFile.Enabled = True

15. Reading File Dim oneline As String Dim datasplit(3) As String Try
While Not (filereader.EndOfStream)
oneline = filereader.ReadLine()
datasplit = oneline.Split(","c)
oneStudent.firstName = datasplit(0)
oneStudent.lastName = datasplit(1)
oneStudent.tele = datasplit(2)
oneStudent.gpa = datasplit(3)
students.Add(oneStudent)
End While
Catch ex As Exception
MessageBox.Show("File has not been open!", "File Error")
End Try
lblMessage.Text = "Total Number of Records Read: " & students.Count

16. Adding Records oneStudent.firstName = txtFirstName.Text
oneStudent.lastName = txtLastName.Text
oneStudent.tele = txtTele.Text
oneStudent.gpa=Convert.ToDecimal(txtGPA.Text)
students.Add(oneStudent)

17. Example 8.14: CreditInquiry.vb
URL:
Enum AccountType
CREDIT
DEBIT
ZERO
End Enum
Using fileChooser As New OpenFileDialog()
result = fileChooser.ShowDialog()
fileName = fileChooser.FileName
End Using

18. Example 8.14: CreditInquiry.vb (cont'd)
URL:
fileReader = New StreamReader(fileName)
Do While Not fileReader.EndOfStream …
Loop
If fileReader IsNot Nothing Then
Try
fileReader.Close()
Catch ex As IOException
End Try
End If
Finally block, guaranteed to be executed