1. Tony Gaddis Kip Irvine STARTING OUT WITH Visual Basic 2008
FOURTH EDITION
Tony Gaddis
Haywood Community College
Kip Irvine
Florida International University

2. Files, Printing, and Structures
Chapter
Files, Printing, and Structures 9
Copyright © 2007 Pearson Education, Inc. Publishing as Pearson Addison-Wesley

3. Introduction 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. Using Files
9.1
A File Is a Collection of Data Stored on a Computer Disk
Information Can Be Saved to Files and Later Reused
Copyright © 2007 Pearson Education, Inc. Publishing as Pearson Addison-Wesley

5. 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

6. 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

7. Reading and Writing to a File
Data must be 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

8. 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

9. Creating Files with StreamWriter Objects
Add Imports System.IO before class declared
Makes StreamWriter classes available in code
A StreamWriter object is used to create a sequential text file in the following way:
Declare an object variable of type StreamWriter
Call CreateText method passing the filename
Method returns a StreamWriter object
Object is assigned to a StreamWriter variable
Variable phoneFile now defines a stream of data that can be written to phonelist.txt
Dim phoneFile As StreamWriter
phoneFile = File.CreateText(“phonelist.txt”)

10. Appending Text with StreamWriter
A StreamWriter object is used to append data to a sequential text file in the following way:
Declare an object variable of type StreamWriter
Call AppendText method passing the filename
Method returns a StreamWriter object
Object is assigned to a StreamWriter variable
Variable phoneFile now defines a stream of data that can be added to the end of phonelist.txt
Dim phoneFile As StreamWriter
phoneFile = File.AppendText(“phonelist.txt”)

11. 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

12. 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 method’s 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()

13. Writing Data to a File Example
Dim studentFile As StreamWriter
studentFile = File.CreateText("StudentData.txt")
studentFile.WriteLine("Jim")
studentFile.WriteLine(95)
studentFile.WriteLine("Karen")
studentFile.WriteLine(98)
studentFile.WriteLine("Bob")
studentFile.WriteLine(82)
studentFile.Close()
The
Resulting
File,
StudentData.txt
Jim 95
Karen 98
Bob 82

14. The StreamWriter Write Method
ObjectVar.Write(Data)
The Write method writes an item of data without writing a newline character
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

15. Closing a StreamWriter Object
Should close files when finished with them
Avoids losing data
Data is initially written to a buffer
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
Tutorial 9-1 provides an example of an application that writes data to a file

16. 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, use:
friendFile = File.AppendText("MyFriends.txt")

17. Appending a File Example
‘Declare an object variable
Dim friendFile as StreamWriter
‘Open the file
friendFile = File.AppendText(“MyFriends.txt”)
‘Write the data
friendFile.WriteLine(“Bill Johnson”)
friendFile.WriteLine(30)
friendFile.WriteLine(“36 Oak Street”)
‘Close the file
friendFile.Close()
friendFile
“After”
Jim Weaver 30
P.O. Box 124
Mary Duncan 24
47 Elm Street
Karen Warren 28
24 Love Lane
Bill Johnson
36 Oak Street
Jim Weaver 30
P.O. Box 124
Mary Duncan 24
47 Elm Street
Karen Warren 28
24 Love Lane
friendFile
“Before”

18. 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
Must have Imports System.IO before class declaration as was done with StreamWriter
Dim ObjectVar As StreamReader
ObjectVar = File.OpenText(Filename)
Dim phoneFile As StreamReader
phoneFile = File.OpenText(“phonelist.txt")

19. 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 StreamReader
custFile = File.OpenText("customer.txt")
custName = custFile.ReadLine()
custName holds the data read from the file
StreamReader also has a Close method

20. 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(filename)
Else
MessageBox.Show(filename & " does not exist.")
End If

21. Detecting the End of a File
The Peek method tests if you’ve 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
Dim scoresFile As StreamReader
Dim strInput As String
scoresFile = File.OpenText("Scores.txt")
Do Until scoresFile.Peek = -1
strInput = scoresFile.ReadLine()
lstResults.Items.Add(input)
Loop
scoresFile.Close()

22. 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
Dim textFile As StreamReader
Dim strInput As String = String.Empty
textFile = File.OpenText("names.txt")
Do While textFile.Peek <> -1
strInput &= Chr(textFile.Read)
Loop
textFile.Close()

23. 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 strInput
Dim textFile As StreamReader
Dim strInput As String
textFile = File.OpenText("names.txt")
strInput = textFile.ReadToEnd
textFile.Close()

24. Write Then Read an Entire Array
Dim intValues(9)
Dim outputFile as StreamWriter
outputFile = File.CreateText("values.txt")
For intCount = 0 To (intValues.Length – 1)
outputFile.WriteLine(intValues(intCount))
Next intCount
outputFile.Close()
Dim inputFile as StreamReader
inputFile = File.OpenText("values.txt")
intValues(intCount) = CInt(inputFile.ReadLine)
inputFile.Close()

25. The OpenFileDialog, SaveFileDialog, FontDialog, and ColorDialog Controls
9.2
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
Copyright © 2007 Pearson Education, Inc. Publishing as Pearson Addison-Wesley

26. OpenFileDialog and SaveFileDialog
Windows has a standard method of allowing a user to choose a file to open or save
These methods let users 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

27. 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

28. 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 (*.*)|*.*"

29. 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

30. 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

31. Open Dialog Box Example
InitialDirectory property
Title property
Filter property

32. 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

33. ColorDialog Control Displays a typical Windows color dialog box
Provides users the ability to choose a color

34. ColorDialog Control 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

35. FontDialog Control Displays a Windows font selection dialog box
Allows users to choose font, font size, etc.

36. FontDialog Control 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

37. The PrintDocument Control
9.3
The PrintDocument Control
The PrintDocument Control Allows You to Print Data to the Printer
Copyright © 2007 Pearson Education, Inc. Publishing as Pearson Addison-Wesley

38. 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

39. 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 the event handler
Basic format of event handler shown below:
Private Sub pdPrint_PrintPage(ByVal sender As System.Object, _
ByVal e As System.Drawing.Printing.PrintPageEventArgs) _
Handles pdPrint.PrintPage
‘Your print code inserted here
End Sub

40. 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
Brushes.Black specifies output in black
DrawString method is formatted as follows:
e.Graphics.DrawString(String, _
New Font(FontName, Size, Style), _
Brushes.Black, HPos, VPos)

41. Specifying Fonts, Sizes, Styles
Fonts are specified with the string which names the font to be used
"Times New Roman"
“Arial" , etc.
Sizes are specified with a number
10, 12, etc.
Print effects are specified with provided constants
FontStyle.Regular
FontStyle.Bold
FontStyle.Underline

42. Sample PrintPage Event Procedure
Private Sub pdPrint_PrintPage(ByVal sender As System.Object, _
ByVal e As System.Drawing.Printing.PrintPageEventArgs) _
Handles pdPrint.PrintPage
Dim inputFile As StreamReader
Dim intX As Integer = 10 ‘Horizontal Position
Dim intY As Integer = 10 ‘Vertical Position
inputFile = File.OpenText(strFilename)
Do While inputFile.Peek <> -1
e.Graphics.DrawString(inputFile.ReadLine, _
New Font("Courier", 10, FontStyle.Regular), _
Brushes.Black, intX, intY)
intY += ‘Increment Vert Pos
Loop
inputFile.Close()
End Sub
Tutorial 9-5 adds a print feature to Tutorial 9-4

43. 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

44. String.Format Example Results in the following output: 50Arg 1 6
String.Format("{0, 7}{1, -10}{2, 7}", 50, "Arg1", 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:
50Arg
7 spaces
10 spaces
Left Justified
7 spaces

45. 9.4
Structures
Visual Basic Allows You to Create Your Own Data Types, in Which You May Group Multiple Data Fields
Copyright © 2007 Pearson Education, Inc. Publishing as Pearson Addison-Wesley

46. 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

47. Syntax for Declaring a Structure
[AccessSpecifier] Structure StructureName
FieldDeclarations
End Structure
StructureName is a name that identifies the structure itself
FieldDeclarations are the declarations of the individual fields within the structure

48. Structure Declaration Example
Following declares a structure with six fields intended to record employee payroll data
Structure name is EmpPayData
Structure EmpPayData
Dim intEmpNumber As Integer
Dim strFirstName As String
Dim strLastName As String
Dim sngHours As Single
Dim decPayRate As Decimal
Dim decGrossPay As Decimal
End Structure

49. 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.strEmpNumber = 1101
deptHead.strFirstName = "Joanne"
deptHead.strLastName = "Smith"
deptHead.sngHours = 40
deptHead.decPayRate = 25
deptHead.decGrossPay = CDec(deptHead.sngHours) * _ deptHead.decPayRate

50. 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 employee’s gross pay
‘ is calculated and stored in the grossPay
‘ field.
With employee
.decGrossPay = .sngHours * .decPayRate
End With
End Sub

51. Structures Containing Arrays
Structures can contain arrays
Must ReDim after declaring structure variable
Structure StudentRecord
Dim strName As String
Dim sngTestScores() As Single
End Structure
Dim student As StudentRecord
ReDim student.sngTestScores(4)
student.strName = "Mary McBride"
student.sngTestScores(0) = 89
Student.sngTestScores(1) = 92
Student.sngTestScores(2) = 84
Student.sngTestScores(3) = 96
Student.sngTestScores(4) = 91

52. 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).empNumber = 1101

53. Modifying the Demetris Leadership Center Application
9.5
Modifying 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
Copyright © 2007 Pearson Education, Inc. Publishing as Pearson Addison-Wesley

54. Changes to Demetris Application
Replace parallel arrays with an array of structure variables
Add option to print sales report
Add options to save & retrieve units sold
Structure ProductData
Dim strName As String ' Item name
Dim strDesc As String ' Descr
Dim intProdNum As Integer ' Item nbr
Dim decPrice As Decimal ' Unit price
Dim intUnitsSold As Integer ' Units sold
End Structure
Const intMAX_SUB As Integer = 8
' Array of ProductData
Dim products(intMAX_SUB) As ProductData