Files, Printing, and Structures

1
Chapter 9

• Files, Printing, and Structures

2
Chapter 9Introduction
3
Chapter 9 Topics

• Saving data to sequential text files
• Reading the data back into an application
• Using the OpenFileDialog, SaveFileDialog,
  ColorDialog, and FontDialog controls
• Using the PrintDocument control to print reports
  from your application
• Packaging units of data together into structures

4
Section 9.1Using Files

• A File Is a Collection of Data Stored on a
  Computer Disk
• Information Can Be Saved to Files and Later
  Reused

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The Life Span of Data

• Thus far, all of our data has been stored in
  controls and variables existing in RAM
• This data disappears once the program stops
  running
• If data is stored in a file on a computer disk,
  it can be retrieved and used at a later time

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Three Steps in Using a File

• The file must be opened
• If it does not yet exist, it will be created
• Data is read from or written to the file
• The program closes the file

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Reading and Writing to a File

• Data must be in retrieved from disk and put in
  memory for an application to work with it
• Data is transferred from disk to memory by
• Reading it from an input file
• Placing it in variables or control properties
• Data is transferred from memory to disk by
• Writing it to an output file
• Getting it from variables or control properties
• Data is frequently placed in the text property of
  a control

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File Types/Access Methods

• Text file type
• Character based text
• Contents can be viewed by Notepad
• Binary file type
• Pure binary form
• Contents cannot be viewed with a text editor
• Access Methods
• Sequential access a continuous stream of data
  written and read as a whole from beginning to end
• Random access access in any order with data
  written to or read from specific places in the
  file
• Like the difference between a casette tape and a
  CD

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Establishing StreamWriter Objects

• A StreamWriter object is used to write to a
  sequential text file in the following way
• Declare a variable of type StreamWriter
• Create a StreamWriter object and assign it to the
  StreamWriter variable using either the
• CreateText method for new files
• AppendText method for existing files
• Variable phoneFile now defines a stream of data
  that can be written to phonelist.txt

Dim phoneFile As System.IO.StreamWriter
phoneFile System.IO.File.CreateText(phonelist.t
xt)
phoneFile System.IO.File.AppendText(phonelist.t
xt)
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Using a String Variable as File Name

• Filename can be a string literal as already shown
  but a string variable is more flexible
• User can select the file they wish to edit
• What if Notepad could only edit textfile.txt?
• Example with string variable as filename
• Can allow the user to enter the filename
• Substitute txtFile.text for customer.txt
• User can then enter filename in a text box

Dim custFile As System.IO.StreamWriter Dim
fileName as String fileName customer.txt custF
ile System.IO.file.AppendText(fileName)
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File Paths

• Filename can include the file path
• Can be a complete file path with drive letter
• C\WordProc\memo.txt"
• Refer to a file in the default drive root
  directory
• "\pricelist.txt"
• Or include no path information at all
• "mytext.txt
• If no path information specified, the bin folder
  of the current project is used

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Writing Data to a File

• The WriteLine method of a StreamWriter object
  actually writes data to the file
• ObjectVar.WriteLine(Data)
• Streamwriter object identified by ObjectVar
• The methods Data argument consists of constants
  or variables with data to be written
• WriteLine appends an invisible newline character
  to the end of the data
• Omit argument to write a blank line to a file
• ObjectVar.WriteLine()

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Closing a StreamWriter Object

• Should close files when finished with them
• Avoids losing data
• Data is initially written to a buffer
• Close writes unsaved data from the buffer to the
  file
• The Close method of a StreamWriter object clears
  the buffer and closes the file
• ObjectVar.Close()
• Streamwriter object identified by ObjectVar

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Writing Data to a File Example
Dim studentFile As System.IO.StreamWriter studentF
ile System.IO.File.CreateText("StudentData.txt")
studentFile.WriteLine("Jim") studentFile.WriteLin
e(95) studentFile.WriteLine("Karen") studentFile.W
riteLine(98) studentFile.WriteLine("Bob") studentF
ile.WriteLine(82) studentFile.Close()
The Resulting File, StudentData.txt
Jim 95 Karen 98 Bob 82

• Tutorial 9-1 is an example of an application that
  writes data to a file

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Importing a Namespace

• System.IO is referred to as a namespace
• A group of logically related classes
• System.IO contains StreamWriter and other file
  related classes
• Can shorten references to such classes by
  importing the namespace in your code
• Imports System.IO
• Allows us to use
• Dim custFile As StreamWriter
• Instead of
• Dim custFile As System.IO.StreamWriter

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Appending to a File

• If opening an existing file with CreateText
• Existing contents are removed
• New text overwrites the old text
• If opening an existing file with AppendText
• Existing contents are retained
• New text adds on to the end of the old text
• If adding a new friend to friendFile, youd use

friendFile System.IO.File.AppendText("MyFriends.
txt")
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The StreamWriter Write Method
ObjectVar.Write(Data)

• The Write method does not place a newline
  character after each data item
• Usually need to provide some sort of delineation
  or delimiter between data items
• A blank space could be used
• Comma is a more common delimiter

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Write Method Example
Dim name As String "Jeffrey Smith" Dim idNum As
Integer 47895 Dim phone As String
"555-7864" outputFile.Write(name) outputFile.Writ
e(" ") outputFile.Write(idNum) outputFile.Write("
") outputFile.WriteLine(phone)
The Resulting File
Jeffrey Smith 47895 555-7864
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StreamReader Objects

• Use StreamReader objects to read from a file
• Define and open similar to StreamWriter
• Sample code
• Variable phoneFile now defines a stream of data
  that can be read from phonelist.txt

Dim ObjectVar As System.IO.StreamReader ObjectVar
System.IO.File.OpenText(Filename)
Dim phoneFile As System.IO.StreamReader phoneFile
System.IO.File.OpenText(phonelist.txt")
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Reading Data from a File

• The ReadLine method of a StreamReader object
  actually reads data from the file
• dataVar ObjectVar.ReadLine()
• Streamwriter object identified by ObjectVar
• The result of the method, the data read from the
  file, is assigned to string variable dataVar
• Sample code
• Dim custFile As System.IO.StreamReader
• custFile System.IO.File.OpenText("customer.txt")
  
• custName custFile.ReadLine()
• custName holds the data read from the file
• StreamReader also has a Close method

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Determining Whether a File Exists

• The File.OpenText method issues a runtime error
  if the file does not exist
• Avoid this by using the File.Exists method
• Format is File.Exists(filename)
• Returns a boolean result that can be tested
• Tutorial 9-2 shows how to read text file data

If System.IO.File.Exists(filename) Then ' Open
the file. inputFile System.IO.File.OpenText(fil
ename) Else MessageBox.Show(filename " does
not exist.") End If
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Detecting the End of a File

• The Peek method tests if youve reached end of
  file (no more characters to read)
• Format is objectvar.Peek
• If no more characters, the value -1 is returned
• Tutorial 9-3 demonstrates the Peek method

Imports System.IO Dim scoresFile As
StreamReader Dim input As String scoresFile
File.OpenText("Scores.txt") Do Until
scoresFile.Peek -1 input scoresFile.ReadLine(
) lstResults.Items.Add(input) Loop scoresFile.Clo
se()
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Read Method

• Read method returns the integer code of the next
  character in the file
• Chr function converts integer code to character
• This loop appends one character at a time to
  input until no more characters are in the file

Imports System.IO Dim textFile As
StreamReader Dim input As String textFile
File.OpenText("names.txt") Do While textFile.Peek
ltgt -1 input Chr(textFile.Read) Loop textFile.C
lose()
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ReadToEnd Method

• ReadToEnd method returns the rest of the file
  from the current read position to end of file
• Functions differently from ReadLine method
• ReadToEnd method ignores line delimiters
• The statement input textFile.ReadToEnd reads
  the file contents and stores it in input

Imports System.IO Dim textFile As
StreamReader Dim input As String textFile
File.OpenText("names.txt") input
textFile.ReadToEnd textFile.Close()
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Write Then Read an Entire Array
Imports System.IO Dim intValues(9) ---------------
--------------------------------- Dim outputFile
as StreamWriter outputFile File.CreateText("valu
es.txt") For count 0 To (intValues.Length
1) outputFile.WriteLine(intValues(count)) Next
count outputFile.Close() -------------------------
----------------------- Dim inputFile as
StreamReader inputFile File.OpenText("values.txt
") For count 0 To (intValues.Length
1) intValues(count) Val(inputFile.ReadLine) Nex
t count inputFile.Close()
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Section 9.2The OpenFileDialog,SaveFileDialog,
FontDialog,and ColorDialog Controls

• Visual Basic Provides Dialog Controls That Equip
  Your Applications With Standard Windows Dialog
  Boxes for Operations Such As Opening Files,
  Saving Files, and Selecting Fonts and Colors

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OpenFileDialog and SaveFileDialog

• Windows has a standard method of allowing a user
  to choose a file to open or save
• Provides users the ability to browse for a file
• The OpenFileDialog and SaveFileDialog controls
  provide this capability in VB
• To use the OpenFileDialog control
• Double click on this tool in the Toolbox
• Appears in component tray
• Use ofd as standard prefix when naming
• SaveFileDialog is used in a similar way

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Displaying an Open Dialog Box

• Display control with the ShowDialog method
• ControlName.ShowDialog()
• Method returns a value indicating which dialog
  box button the user selects, either
• DialogResult.OK, or
• DialogResult.Cancel
• For example

If ofdOpenfile.Showdialog() DialogResult.OK
Then MessageBox.Show(ofdOpenFile.FileName) Else
MessageBox.Show(You selected no file) End If
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Dialog Box Filter Property

• FileDialog controls have a Filter property
• Limits files shown to specific file extensions
• Specify filter description shown to user first
• Then specify the filter itself
• Pipe symbol () used as a delimiter
• Following Filter property lets user choose
• Text files (.txt), displays all .txt files
• All files (.), displays all file extensions

ofdOpenFile.Filter "Text files (.txt).txt"
_ "All files (.)."
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Other OpenFileDialog Properties

• InitialDirectory property specifies folder to use
• Default if not specified is current folder
• To set dialog box initial directory to C\Data
• ofdOpenFile.InitialDirectory C\Data
• Title property specifies the text on the title
  bar
• Default title is Open if not specified
• ofdOpenFile.Title Select a File to Open
• Filename property returns file selected from
  dialog box by user, in this case to selectedFile
• selectedFile ofdOpenFile.Filename

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Open Dialog Box Example

• User may choose to display .txt files or all
  files
• Files from Data folder of hard drive are shown
• Dialog box title shows Select a File to Open
• Variable inputFile holds file selected by user

' Configure the Open dialog box and display
it. With ofdOpenFile .Filter "Text files
(.txt).txt" _ "All files
(.)." .InitialDirectory "C\Data" .Title
"Select a File to Open" If .ShowDialog()
DialogResult.OK Then inputFile
System.IO.File.OpenText(.Filename) End If End
With
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SaveFileDialog Control

• SaveFileDialog uses the same methods
• ShowDialog()
• The same properties
• Filter
• InitialDirectory
• Title
• Filename
• And the same result constants
• DialogResult.OK
• DialogResult.Cancel
• Tutorial 9-4 uses these controls in a text editor

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ColorDialog Control

• Displays a typical Windows color dialog box
• Provides users the ability to choose a color
• To use the ColorDialog control
• Double click the tool in the Toolbox
• Appears in component tray
• Use cd as standard prefix when naming
• The following code sets the text in control
  lblMessage to the color selected by the user

cdColor.ShowDialog() If cdColor.ShowDialog()
DialogResult.OK Then lblMessage.ForeColor
cdColor.Color End If
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FontDialog Control

• Displays a Windows font selection dialog box
• Allows users to choose font, font size, etc.
• To use the FontDialog control
• Double click the tool in the Toolbox
• Appears in component tray
• Use fd as standard prefix when naming
• The following code sets the text in control
  lblMessage to the font selected by the user

fdFont.ShowDialog() If fdFont.ShowDialog()
DialogResult.OK Then lblMessage.Font
fdFont.Font End If
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Section 9.3The PrintDocument Control

• The PrintDocument Control Allows You to Print
  Data to the Printer

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PrintDocument Control

• Allows you to send output to the printer
• To use the PrintDocument control
• Double click the tool in the Toolbox
• Appears in component tray
• Use pd as standard prefix when naming
• PrintDocument control has a Print method
• This method starts the printing process
• Format is
• PrintDocumentControl.Print()
• This triggers a PrintPage event

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PrintPage Event Handler

• The code in the PrintPage event handler performs
  the actual printing
• Double click PrintDocument control in tray
• This creates the PrintPage event handler
• Insert your print code inside event handler
• Basic format of event handler is as follows

Private Sub pdPrint_PrintPage(ByVal sender As
System.Object, _ ByVal e As System.Drawing.Printi
ng.PrintPageEventArgs) _ Handles
pdPrint.PrintPage Your print code here End Sub
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DrawString Method

• The DrawString method is used inside the
  PrintPage event to
• Specify data to send to the printer in string
• Set font, font size, and font style
• Determine horizontal position (HPos) of text
• Determine vertical position (VPos) of text
• DrawString method is formatted as follows

e.Graphics.DrawString(String, _ New
Font(FontName, Size, Style), _ Brushes.Black,
HPos, VPos)
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Specifying Fonts, Sizes, Styles

• Fonts are specified with the string which names
  the font to be used
• "Times New Roman"
• Sizes are specified with a number
• 12
• Styles are specified with provided constants
• FontStyle.Regular
• FontStyle.Bold
• FontStyle.Underline

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Sample PrintPage Event Procedure
Private Sub pdPrint_PrintPage(ByVal sender As
System.Object, _ ByVal e As System.Drawing.Printi
ng.PrintPageEventArgs) _ Handles
pdPrint.PrintPage Dim inputFile As
System.IO.StreamReader Dim x As Integer
10 Horizontal Position Dim y As Integer
10 Vertical Position inputFile
System.IO.File.OpenText(filename) Do While
inputFile.Peek ltgt -1 e.Graphics.DrawString(inputF
ile.ReadLine, _ New Font("Courier", 10,
FontStyle.Regular), _ Brushes.Black, x, y) y
12 Increment Vert Pos Loop inputFile.Close(
) End Sub

• Tutorial 9-5 adds a print feature to Tutorial 9-4

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Printing Column Based Reports

• Business reports typically contain a
• Report header printed at the top of the page
• Report body with the data, usually in columns
• Optional footer, often totalling certain columns
• Report header usually has column headings
• Monospaced font used for column reports
• Each character takes same amount of space
• This allows columns to be aligned
• String.Format used to align data along column
  boundaries

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String.Format Example
String.Format("0, 101, 102, 10", 50, "Arg
1", 6)
Argument 0
Specifies the argument number
Argument 1
Argument 2
Specifies field width for arg negative - left
justified positive - right justified
Results in the following output
50 Arg 1 6
10 spaces
10 spaces
10 spaces
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Section 9.4Structures

• Visual Basic Allows You to Create Your Own Data
  Types, in Which You May Group Multiple Data Fields

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Structures vs. Arrays

• Arrays
• Multiple fields in one array
• All of the same data type
• Distinguished by a numerical index
• Structures
• Multiple fields in one structure
• Can be of differing data types
• Distinguished by a field name

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Syntax for Declaring a Structure
AccessSpecifier Structure StructureName FieldDe
clarations End Structure

• StructureName is a name that identifies the
  structure itself
• FieldDeclarations are the declarations of the
  individual fields within the structure

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Structure Declaration Example

• Following declares a structure with six fields
  intended to record employee payroll data
• Structure name is EmpPayData

Structure EmpPayData Dim empNumber As
Integer Dim firstName As String Dim lastName As
String Dim hours As Single Dim payRate As
Decimal Dim grossPay As Decimal End Structure
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Creating and Initializing a Structure

• Using the EmpPayData structure just defined
• Define variable deptHead of type EmpPayData
• deptHead contains the six fields in the structure
• Access each field using varName.fieldName

Dim deptHead As EmpPayData deptHead.empNumber
1101 deptHead.firstName "Joanne" deptHead.lastNa
me "Smith" deptHead.hours 40 deptHead.payRate
25 deptHead.grossPay deptHead.hours
deptHead.payRate
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Passing Structure Variables to Procedures and
Functions

• Structures can be passed to procedures and
  functions like any other variable
• The data type to use in the specification is the
  name of the structure

Sub CalcPay(ByRef employee as EmpPaydata) This
procedure accepts an EmpPayData variable as
its argument. The employees gross pay is
calculated and stored in the grossPay
field. With employee .decGrossPay .sngHours
.decPayRate End With End Sub
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Structures Containing Arrays

• Structures can contain arrays
• Must ReDim after declaring structure variable

Structure StudentRecord name As
String testScores() As Single End Structure Dim
student As StudentRecord ReDim student.TestScores(
4) student.name "Mary McBride" student.testScore
s(0) 89 student.testScores(1)
92 student.testScores(2) 84 student.testScores(3
) 96 student.testScores(4) 91
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Arrays Containing Structures

• Can declare an array of structures
• Example below declares employees as an array of
  type EmpPayData with 10 elements
• Can refer to each field using the format
• arrayName(index).fieldName
• Tutorial 9-6 examines an application with a
  structure

Dim employees(9) As EmpPayData ' Refer to the
empNumber of the first employee employees(0).empNu
mber 1101
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Section 9.5Modifying the Demetris Leadership
Center Application

• Modify this application to include the ability to
  save and retrieve data,
• use an array of structure variables instead of
  parallel arrays,
• print the sales report