Chapter 9: Sequential Access Files and Printing

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Chapter 9 Sequential Access Files and Printing
Programming with Microsoft Visual Basic .NET,
Second Edition
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Sequential Access FilesLesson A Objectives

• Declare StreamReader and StreamWriter variables
• Open a sequential access file
• Determine whether a sequential access file exists
• Write information to a sequential access file
• Align the text written to a sequential access file

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Sequential Access FilesLesson A Objectives
(continued)

• Read information from a sequential access file
• Determine whether the computer has finished
  reading a sequential access file
• Close a sequential access file

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File Types

• Files to which information is written are called
  output files
• The files store the output produced by an
  application
• Files that are read by the computer are called
  input files
• An application uses the information in these
  files as input

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File Types (continued)

• Here is a list of different file types
• Sequential access files
• Random access files
• Binary access files

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Using Sequential Access Files

• A sequential access file is often referred to as
  a text file, because it is composed of lines of
  text
• Sequential access files are similar to cassette
  tapes in that each line in the file, like each
  song on a cassette tape, is both stored and
  retrieved in consecutive order (sequentially)

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Using Sequential Access Files (continued)
Figure 9-5 Procedure for using a sequential
access file
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Declaring StreamWriter and StreamReader Variables

• Use a StreamWriter object to write a sequence of
  characters to a sequential access file
• The sequence of characters is referred to as a
  stream of characters (or a stream)
• Use a StreamReader object to read a stream
  (sequence of characters) from a sequential access
  file

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Declaring StreamWriter and StreamReader Variables
(continued)

• Before creating the appropriate object, first
  declare an object variable to store the address
  of the object in the computers internal memory
• Use a StreamWriter variable to store the address
  of a StreamWriter object
• Use a StreamReader variable to store the address
  of a StreamReader object

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Declaring StreamWriter and StreamReader Variables
(continued)
Figure 9-6 Syntax and examples of declaring
StreamWriter and StreamReader variables
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Opening a Sequential Access File

• The OpenText method opens an existing sequential
  access file for input and allows the computer to
  read the information stored in the file
• Use the CreateText method to create a new, empty
  sequential access file to which data can be
  written
• Use the AppendText method to add data to the end
  of an existing sequential access file

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Opening a Sequential Access File (continued)
Figure 9-7 Syntax and examples of opening a
sequential access file
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Opening a Sequential Access File (continued)
Figure 9-7 Syntax and examples of opening a
sequential access file (continued)
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Opening a Sequential Access File (continued)
Figure 9-8 Position of the file pointer when
files are opened for input, output, and append
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Determining Whether a File Exists

• Avoid errors by using the Exists method
• Syntax IO.File.Exists(filename)
• The Exists method returns the Boolean value True
  if filename exists otherwise, it returns the
  Boolean value False

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Writing Information to a Sequential Access File

• Use either the Write method or the WriteLine
  method to write information to a sequential
  access file
• Write method
• Positions the file pointer at the end of the last
  character it writes to the file
• Syntax variablename.Write(data)

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Writing Information to a Sequential Access File
(continued)

• WriteLine method
• Positions the file pointer at the beginning of
  the next line in the file
• Syntax variablename.WriteLine(data)

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Reading Information from a Sequential Access File

• ReadLine method
• Read a line of text from the file
• Syntax variablename.ReadLine()
• Peek method
• Looks to see if there is another character to
  read
• Syntax variablename.Peek()

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Closing a Sequential Access File

• Close method closes the file when you are
  finished
• Syntax variablename.Close()
• Variablename is the name of either a StreamReader
  or StreamWriter variable

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The Friends Application

• Allows the user to
• Write the names of his or her friends to a
  sequential access file
• Read the names from the file

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The Friends Application (continued)
Figure 9-14 User interface for the Friends
application
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The Friends Application (continued)
Figure 9-15 Pseudocode for the Write to File and
Read from File buttons
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Records In a Sequential Access File Lesson B
Objective

• Write records to a sequential access file
• Read records from a sequential access file

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Writing and Reading Records

• A sequential access file can be used to store
  fields and records
• A field is a single item of information about a
  person, place, or thing
• A record is one or more related fields that
  contain all of the necessary data about a
  specific person, place, or thing

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Writing and Reading Records (continued)

• When writing records to a sequential access file,
  you typically write each record on a separate
  line in the file
• If the records contain more than one field, you
  can separate each field with a special character,
  such as a comma or the number symbol ()

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Writing and Reading Records (continued)
Figure 9-21 Examples of writing a record to a
sequential access file
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Writing and Reading Records (continued)
Figure 9-22 Examples of reading records from a
sequential access file
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Creating the PAO Application

• Application for the PAO (Political Awareness
  Organization) should allow the organizations
  secretary to
• Save (to a sequential access file) a voters
  political party and age
• Tabulate the number of Democrats, Republicans,
  and Independents entered in the file
• Print the contents of the file

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Creating the PAO Application (continued)
Figure 9-23 Interface for the PAO application
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Coding the PaoForm Load Event Procedure
Figure 9-25 Pseudocode for the PaoForms Load
event procedure
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Coding the uiWriteButton Click Event Procedure
Figure 9-30 Pseudocode for the uiWriteButtons
Click event procedure
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Coding the uiDisplayButton Click Event Procedure
Figure 9-34 Pseudocode for the uiDisplayButtons
Click event procedure
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Coding the uiDisplayButton Click Event Procedure
(continued)
Figure 9-34 Pseudocode for the uiDisplayButtons
Click event procedure (continued)
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Printing a Sequential Access FileLesson C
Objective

• Add a PrintDocument control to a form
• Print text using the Print and e.Graphics.DrawStri
  ng methods
• Code a PrintDocument controls PrintPage event
  procedure

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Adding a PrintDocument Control to the Form

• To complete the PAO application, you need to
• Add a PrintDocument control to the form
• Code the Print Report buttons Click event
  procedure and the PrintDocument controls
  PrintPage event procedure

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Coding the Print Report Button Click Event
Procedure

• The Print Report buttons Click event procedure
  is responsible for using the uiReportPrintDocument
  control to print the contents of the pao.txt
  sequential access file
• The Print method causes the PrintDocument
  controls PrintPage event to occur
• You use the PrintPage event to indicate the
  information you want to print, as well as how you
  want the information to appear in the printout

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Coding the Print Report Button Click Event
Procedure (continued)
Figure 9-39 Pseudocode for the Print Report
buttons Click event procedure
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Coding the PrintPage Event Procedure

• The PrintPage event procedure should print the
  contents of the pao.txt file in a report format
• The report should contain a report header and two
  columns of information
• The first column should list the party
• The second column should list the age

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Coding the PrintPage Event Procedure (continued)
Figure 9-41 Pseudocode for the
uiReportPrintDocuments PrintPage event procedure
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The e.Graphics.DrawString Method

• You use the e.Graphics.DrawString method to print
  text on the printer
• Some print fonts are proportionally spaced, while
  others are fixed-spaced, often referred to as
  mono-spaced

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The e.Graphics.DrawString Method (continued)

• Fixed-spaced fonts use the same amount of space
  to print each character
• Proportionally spaced fonts use varying amounts
  of space to print characters

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Summary

• To declare a StreamWriter or StreamReader
  variable, use the syntaxDim Private
  variablename As IO.objecttype
• To open a sequential access file for input, use
  the syntax IO.File.OpenText(filename)
• To open a sequential access file for append, use
  the syntax IO.File.AppendText(filename)
• To open a sequential access file for output, use
  the syntax IO.File.CreateText(filename)

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Summary (continued)

• To write a record to a sequential access file,
  you typically write each record on a separate
  line in the file
• If the records contain more than one field,
  separate each field with a special character
• To read a record from a sequential access file,
  use the ReadLine method to read a line of text
  from the file the line of text is the record

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Summary (continued)

• To print text within a Visual Basic .NET
  application
• Include a PrintDocument control in the
  application
• Use the Print method to print the document
• Use the PrintPage event procedure to indicate the
  information you want to print and how you want
  the information to appear in the printout
• Use the syntax e.Graphics.DrawString(string,
  font, Brushes.Black, horizontalPosition,
  verticalPosition) to print the document