1. Files, Printing, and Structures
Chapter 9
Files, Printing, and Structures

2. Chapter 9 Introduction

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

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 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

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. 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.txt”)
phoneFile = System.IO.File.AppendText(“phonelist.txt”)

10. 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”
custFile = System.IO.file.AppendText(fileName)

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. 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

14. Writing Data to a File Example
Dim studentFile As System.IO.StreamWriter
studentFile = System.IO.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
Tutorial 9-1 is an example of an application that writes data to a file

15. 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

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, you’d use
friendFile = System.IO.File.AppendText("MyFriends.txt")

17. 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

18. Write Method Example Dim name As String = "Jeffrey Smith"
Dim idNum As Integer = 47895
Dim phone As String = " "
outputFile.Write(name)
outputFile.Write(" ")
outputFile.Write(idNum)
outputFile.WriteLine(phone)
The
Resulting
File
Jeffrey Smith

19. 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")

20. 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

21. 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

22. 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
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.Close()

23. 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 <> -1
input &= Chr(textFile.Read)
Loop
textFile.Close()

24. 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()

25. Write Then Read an Entire Array
Imports System.IO
Dim intValues(9)
Dim outputFile as StreamWriter
outputFile = File.CreateText("values.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")
intValues(count) = Val(inputFile.ReadLine)
inputFile.Close()

26. Section 9.2 The 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

27. 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

28. 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

29. 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 (*.*)|*.*"

30. 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

31. 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

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
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

34. 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

35. Section 9.3 The PrintDocument Control
The PrintDocument Control Allows You to Print Data to the Printer

36. 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

37. 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.Printing.PrintPageEventArgs) _
Handles pdPrint.PrintPage
‘Your print code here
End Sub

38. 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)

39. 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

40. 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 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 <> -1
e.Graphics.DrawString(inputFile.ReadLine, _
New Font("Courier", 10, FontStyle.Regular), _
Brushes.Black, x, y)
y += ‘Increment Vert Pos
Loop
inputFile.Close()
End Sub
Tutorial 9-5 adds a print feature to Tutorial 9-4

41. 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

42. String.Format Example Results in the following output: 50 Arg 1 6
String.Format("{0, 10}{1, 10}{2, 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:
Arg
10 spaces
10 spaces
10 spaces

43. Section 9.4 Structures
Visual Basic Allows You to Create Your Own Data Types, in Which You May Group Multiple Data Fields

44. Structures vs. Arrays Arrays: Structures 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

45. 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

46. 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

47. 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.lastName = "Smith"
deptHead.hours = 40
deptHead.payRate = 25
deptHead.grossPay = deptHead.hours * deptHead.payRate

48. 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

49. 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.testScores(0) = 89
student.testScores(1) = 92
student.testScores(2) = 84
student.testScores(3) = 96
student.testScores(4) = 91

50. 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

51. Section 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