Chapter 9: Sequential Access Files
and Printing
Programming with Microsoft Visual Basic
.NET, Second Edition
Sequential Access Files
Lesson 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 Files
Lesson 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 computer’s 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 organization’s
secretary to:
– Save (to a sequential access file) a voter’s 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 PaoForm’s Load event
procedure
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Coding the uiWriteButton Click Event
Procedure
Figure 9-30: Pseudocode for the uiWriteButton’s Click event
procedure
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Coding the uiDisplayButton Click
Event Procedure
Figure 9-34: Pseudocode for the uiDisplayButton’s Click event
procedure
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Coding the uiDisplayButton Click
Event Procedure (continued)
Figure 9-34: Pseudocode for the uiDisplayButton’s Click event
procedure (continued)
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Printing a Sequential Access File
Lesson C Objective
• Add a PrintDocument control to a form
• Print text using the Print and
e.Graphics.DrawString methods
• Code a PrintDocument control’s 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 button’s Click event
procedure and the PrintDocument control’s
PrintPage event procedure
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Coding the Print Report Button Click
Event Procedure
• The Print Report button’s 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
control’s 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 button’s 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 uiReportPrintDocument’s
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 syntax:
{Dim | 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
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