Tutorial 9 Sequential Access Files and Printing

Sequential Access Files Lesson A Objectives 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 Tutorial 9: Sequential Access Files and Printing

File Types 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 Tutorial 9: Sequential Access Files and Printing

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) Tutorial 9: Sequential Access Files and Printing

Procedure for Using a Sequential Access File Declare either a StreamWriter or StreamReader object variable Create a StreamWriter or StreamReader object by opening a file; assign the object’s address to the object variable declared in Step 1 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 Use the StreamWriter or StreamReader object to close the file Tutorial 9: Sequential Access Files and Printing

Using StreamWriter and StreamReader Objects 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 Tutorial 9: Sequential Access Files and Printing

Opening a Sequential File 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”) Tutorial 9: Sequential Access Files and Printing

Does the file exist? 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 Tutorial 9: Sequential Access Files and Printing

Writing to a Sequential File 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 Tutorial 9: Sequential Access Files and Printing

Formatting String Data 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) Tutorial 9: Sequential Access Files and Printing

Aligning Data in a Sequential File 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 Tutorial 9: Sequential Access Files and Printing

Reading from a Sequential File 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 Close method – Close the file when you are finished objStreamReader.Close() objStreamWriter.Close() Tutorial 9: Sequential Access Files and Printing

Using a DateTimePicker Control Lesson B Objectives 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 Tutorial 9: Sequential Access Files and Printing

Adding a DateTimePicker Control to a Form The DateTimePicker control allows the user to select either a date or time, and then displays the selected information in a specified format Tutorial 9: Sequential Access Files and Printing

The ShowUpDown Property 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 Tutorial 9: Sequential Access Files and Printing

The Format Property You can use the Format property to control the format (style) of the date or time displayed in the DateTimePicker control Tutorial 9: Sequential Access Files and Printing

Tutorial 9: Sequential Access Files and Printing

The Value Property 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 Tutorial 9: Sequential Access Files and Printing

The Value Property Example Results Me.PayDateTimePicker.Value 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 Tutorial 9: Sequential Access Files and Printing

Using the DateTime Object 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) Tutorial 9: Sequential Access Files and Printing

Retrieving the Information Stored in the Value Property Example using “11/12/2004 9:07 AM” Results Me.PayDateTimePicker.Value.Month 11 Me.PayDateTimePicker.Value.Day 12 Me.PayDateTimePicker.Value.Year 2004 Me.PayDateTimePicker.Value.DayOfWeek 5 Me.PayDateTimePicker.Value.DayOfWeek.ToString Friday Me.PayDateTimePicker.Value.Hour 9 Me.PayDateTimePicker.Value.Minute 7 Me.PayDateTimePicker.Value.Second Tutorial 9: Sequential Access Files and Printing

Text Property 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 Tutorial 9: Sequential Access Files and Printing

Tutorial 9: Sequential Access Files and Printing

Retrieving the System Date and Time 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) Tutorial 9: Sequential Access Files and Printing

Coding the CarriageForm Load Event Procedure 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

Tutorial 9: Sequential Access Files and Printing

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

Tutorial 9: Sequential Access Files and Printing

Completing the Carriage House Application Lesson C Objective 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 Tutorial 9: Sequential Access Files and Printing

Adding a PrintDocument Control to the Form Before you can print a document within a Windows application, you need to add a PrintDocument control to the form Tutorial 9: Sequential Access Files and Printing

Coding the Print Report Button’s Click Event Procedure 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 Tutorial 9: Sequential Access Files and Printing

Tutorial 9: Sequential Access Files and Printing

Coding the PrintPage Event Procedure 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 Tutorial 9: Sequential Access Files and Printing

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 Fixed-spaced fonts use the same amount of space to print each character Proportionally spaced fonts use varying amounts of space to print characters Tutorial 9: Sequential Access Files and Printing