Tutorial 9: Sequential Access Files and Printing 1

After completing this lesson, you will be able to:
 Declare StreamReader and StreamWriter object variables
 Open a sequential access file
 Determine whether a sequential file exists
 Write information to a sequential access file
 Align the text written to a sequential access file
 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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 Files to which information is written are called output files , because the files store the output produced by an application
 Files that are read by the computer are called input files , because an application uses the information in these files as input
 Here is a list of different file types:
 Sequential access files
 Random access files
 Binary access files
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 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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1. Declare either a StreamWriter or StreamReader object variable
2. Create a StreamWriter or StreamReader object by opening a file; assign the object’s address to the object variable declared in Step 1
3. Use the StreamWriter object to write one or more lines of text to the file, or use the StreamReader object to read one or more lines of text from the file
4. Use the StreamWriter or StreamReader object to close the file
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Dim strLine As String, objStreamReader As System.IO.StreamReader
'determine whether the file.txt file exists
If System.IO.File.Exists("file.txt") = True Then
'create a StreamReader object by opening the file for input objStreamReader = System.IO.File.OpenText("file.txt")
'process the loop instructions until there are no more characters to read
Do Until objStreamReader.Peek = -1
'read a line of text from the file strLine = objStreamReader.ReadLine()
'display the line in a message box
MessageBox.Show(strLine, "File Example", _
MessageBoxButtons.OK, MessageBoxIcon.Information)
Loop
'close the file objStreamReader.Close()
Else
'display an appropriate message
MessageBox.Show("The file.txt file does not exist.", "File Example", _
MessageBoxButtons.OK, MessageBoxIcon.Information)
End If
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'declare a StreamWriter object variable
Dim objStreamWriter As System.IO.StreamWriter
'create a StreamWriter object by opening the file for append objStreamWriter = System.IO.File.AppendText("file.txt")
'write a line of text to the file objStreamWriter.WriteLine(Me.NameTextBox.Text)
'close the file objStreamWriter.Close()
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In Visual Basic .NET
 Use a StreamWriter object to write a sequence of characters —referred to as a stream of characters or, more simply, a stream —to a sequential access file
 Use a StreamReader object to read a stream (sequence of characters) from a sequential access file
 Before you create the appropriate object, you first must declare an object variable to store the address of the object in the computer’s internal memory
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 Refer to Figure 9-7 in the textbook, which illustrates all of the methods used to open a sequential access file
 CreateText method – Creates a file for writing a text stream objStreamWriter = System.IO.File.CreateText(“memo.txt”)
 AppendText method – Opens a file appending text to the end of the file objStreamWriter = System.IO.File.AppendText(“sales.txt”)
 OpenText method – Opens a file to read a stream of text objStreamReader = System.IO.File.OpenText(“a:\reports\pay.txt”)
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 Avoid errors by using the Exists method
If System.IO.File.Exists(“pay.txt”) Then
 Returns True or False
 The Exists method returns the Boolean value True if
filename exists; otherwise, it returns the Boolean value
False
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Write method Leaves the file pointer after last character objStreamWriter.Write(“Good”) objStreamWriter.Write(“ Morning”) ‘ Writes on the same line
Good Morning
WriteLine method Appends the line terminator to the end of line and leaves the file pointer ready for next line objStreamWriter.WriteLine(“Good”) objStreamWriter.WriteLine(“ Morning”) ’ Each is on a separate line
Good
Morning
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 The Space function inserts spaces objStreamWriter.Write(Space(10) & “A” & Space(5) & “B”
 PadLeft – Pads a string on the left with specified character
Dim sngNetPay As Single = 767.89, strNet As String strNet = FormatCurrency (sngNetPay) strNet = strNet.PadLeft(15, “*”)
Results in “********$767.89”
 PadRight – Pads a string on the right with specified character
Dim strName As String = “Sue” strName = strName.PadRight(10)
Results in “Sue ” (the string “Sue” and seven spaces)
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For intRegion = 1 To 3 strSales = InputBox(“Sales amount”, “Sales”) strSales = Format(strSales, “standard”) objStreamWriter.WriteLine(strSales.PadLeft(8))
Next intRegion
Result (assuming the following sales amounts: 645.75, 1200, 40.80
645.75
1,200.00
40.80
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 ReadLine Method – Read a line of text from the file strLine = objStreamReader.ReadLine()
 Peek method – Looks to see if there is another character to read
Do Until objStreamReader.Peek = -1
 ReadToEnd
Reads the stream from the current position to the end of the stream.
strContent = objStreamReader.ReadToEnd()
 Close method – Close the file when you are finished objStreamReader.Close() objStreamWriter.Close()
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 Download and Open the “Seqfile” Zip folder
 Read Tutorial 9 Lesson A
 Run laFile solution
 Read page 571 exercise 14
 Run laModified File solution
 Read page 572 exercise 15
 Run laImports File solution
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After completing this lesson, you will be able to:
 Add a DateTimePicker control to a form
 Control the appearance of a DateTimePicker control
 Format the text that appears in a DateTimePicker control
 Set and retrieve the information stored in a
DateTimePicker control
 Retrieve the system date and time
 Display a form immediately
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 The
DateTimePicker control allows the user to select either a date or time, and then displays the selected information in a specified format
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 The DateTimePicker control’s ShowUpDown property determines whether a list arrow button or up and down arrow button appear on the control
 If the property is set to its default value, False, the control contains a list arrow button
 If, on the other hand, the ShowUpDown property is set to True, up and down arrow buttons appear on the control
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
You can use the Format property to control the format (style) of the date or time displayed in the DateTimePicker control
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 When you add a DateTimePicker control to a form, Visual Basic .NET retrieves the current date and time from your computer system’s clock, and assigns both values to the DateTimePicker control’s Value property
 You can verify that fact by viewing the Value property in the Properties list
 The DateTime object is simply an object that represents a date and an optional time
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Example Results
Me.PayDateTimePicker.Value 11/12/2004 9:07:00 AM
Me.PayDateTimePicker.Value.ToLongDateString Friday, November 12, 2004
Me.PayDateTimePicker.Value.ToShortDateString 11/12/2004
Me.PayDateTimePicker.Value.ToLongTimeString 9:08:00 AM
Me.PayDateTimePicker.Value.ToShortTimeString 9:08 AM
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objectname.Value = New DateTime(year, month, day[, hour, minute, second])
Me.PayDateTimePicker.Value = New DateTime(2004, 2, 3)
Me.PayDateTimePicker.Value = New DateTime(2004, 9, 7, 5, 30, 18)
Me.PayDateTimePicker.Value = New DateTime(2004, 1, 6, 17, 30, 18)
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Example using “11/12/2004 9:07 AM”
Me.PayDateTimePicker.Value.Month
Me.PayDateTimePicker.Value.Day
Me.PayDateTimePicker.Value.Year
Me.PayDateTimePicker.Value.DayOfWeek
Me.PayDateTimePicker.Value.DayOfWeek.ToString
Me.PayDateTimePicker.Value.Hour
Me.PayDateTimePicker.Value.Minute
Me.PayDateTimePicker.Value.Second
Results
11
12
2004
9
7
0
5
Friday
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 The text that appears in a DateTimePicker control is stored in the control’s Text property
 Visual Basic .NET automatically assigns to the Text property the contents of the Value property formatted using the setting specified in the Format property; this is illustrated in
Figure 9-31 of the textbook
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 The system date is the current date according to your computer system’s clock
 The system time is the current time according to your computer system
 You can retrieve the system time using the syntax
TimeOfDay[.methodname], where methodname
(which is optional) is ToLongTimeString,
ToShortTimeString, or ToString(formatting characters)
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 The pseudocode for the CarriageForm Load event procedure is shown in Figure 9-34
 The syntax of the form’s Show method is simply Me.Show()
Tutorial 9: Sequential Access Files and Printing 28

Tutorial 9: Sequential Access Files and Printing 29

 The pseudocode for the AddButton Click event is shown in Figure 9-40 of the textbook
Tutorial 9: Sequential Access Files and Printing 30

Tutorial 9: Sequential Access Files and Printing 31

After completing this lesson, you will be able to:

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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 Before you can print a document within a
Windows application, you need to add a
PrintDocument control to the form
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 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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 In this case, the PrintPage event procedure should print the contents of the events.txt file in a report format
 The report should contain a report header , which describes the contents of the report, and three columns of information
 The first column should list the event names, the second column the event dates, and the third column the event prices
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 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
 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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