Chapter 9 Files, Printing, and Structure Topics Using Files The OpenFileDialog, SaveFileDialog, FontDialog, and ColorDialog Controls The PrintDocument Control Structures

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

Three Steps in Using a File 1. The file must be opened If it does not yet exist, it will be created 2. Data is read from or written to the file 3. The program closes the file

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

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 cassette tape and a CD

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 Dim phoneFile As StreamWriter –Call CreateText method passing the filename phoneFile = File.CreateText("phonelist.txt") –This 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

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 Dim phoneFile As StreamWriter –Call AppendText method passing the filename phoneFile = File.AppendText("phonelist.txt") –This Method AppendText 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

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

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()

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() Jim 95 Karen 98 Bob 82 The Resulting File, StudentData.txt

The StreamWriter Write Method 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 ObjectVar.Write(Data)

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

Appending to a File If opening an existing file with CreateText –Existing contents are deleted –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")

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 Elm Street Karen Warren Love Lane friendFile “Before” Jim Weaver 30 P.O. Box 124 Mary Duncan Elm Street Karen Warren Love Lane Bill Johnson Oak Street

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")

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

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

Detecting End of 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()

Detecting End of File (Cont’d) The EndofStream method also tests if you’ve reached end of file (no more characters to read) –Format is objectvar.EndOfStream –If no more characters, the value True is returned Dim scoresFile As StreamReader Dim strInput As String scoresFile = File.OpenText("Scores.txt") Do Until scoresFile.EndOfStream() strInput = scoresFile.ReadLine() lstResults.Items.Add(input) Loop scoresFile.Close()

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()

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

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

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

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 (*.*)|*.*"

Open Dialog Box Example InitialDirectory property Title property Filter property

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

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

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

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

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

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

PrintPage Event Handler 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 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:

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)

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

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 += 12'Increment Vert Pos Loop inputFile.Close() End Sub Tutorial 9-5 adds a print feature to Tutorial 9-4

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

String.Format Example String.Format("{0, 7}{1, -10}{2, 7}", 50, "Arg1", 6) Specifies the argument number Specifies field width for arg negative - left justified positive - right justified Argument 0 Argument 1 Argument 2 Results in the following output: 50Arg spaces10 spaces Left Justified 7 spaces

Other OpenFileDialog Properties InitialDirectory property specifies folder to use –Default if not specified is the 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

Open Dialog Box Example ' 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 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

Structures A Visual Basic programmer may also create new data types, called user-defined data types (UDT). Two kinds of UDTs: structure and class. This chapter discusses the use of structure and Chapter 12 the use of class.

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

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

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

Creating and Initializing a Structure Dim deptHead As EmpPayData deptHead.intEmpNumber = 1101 deptHead.strFirstName = "Joanne" deptHead.strLastName = "Smith" deptHead.sngHours = 40 deptHead.decPayRate = 25 deptHead.decGrossPay = CDec(deptHead.sngHours) * _ deptHead.decPayRate 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

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

Structures Containing Arrays 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 Structures can contain dynamic arrays Must ReDim after declaring structure variable

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 Arrays Containing Structures Dim employees(9) As EmpPayData ' Refer to the empNumber of the first employee employees(0).empNumber = 1101