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VB File Processing

VB File Processing. The Process of Using a File . The file must be opened. Data is either written to the file or read from the file. When the application is finished using the file, the file is closed. Types of Text File. Sequential text file HTML file, Email file, etc.

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VB File Processing

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  1. VB File Processing

  2. The Process of Using a File • The file must be opened. • Data is either written to the file or read from the file. • When the application is finished using the file, the file is closed.

  3. Types of Text File • Sequential text file • HTML file, Email file, etc. • Comma-Delimited file • "s5","peter",3.5 • "s1","paul",3 • "s7","mary",2 • Random access file

  4. x-sender: me@dchaolaptop x-receiver: you@dchaolaptop Received: from mail pickup service by dchaolaptop with Microsoft SMTPSVC; Mon, 19 May 2003 11:27:02 -0700 From: <me> To: <you@dchaolaptop> Subject: testReply6 Date: Mon, 19 May 2003 11:27:01 -0700 Message-ID: <008e01c31e34$3d982660$0100007f@dchaolaptop> MIME-Version: 1.0 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: 7bit X-Mailer: Microsoft CDO for Windows 2000 Thread-Index: AcMeND2WJSRAs2TDR6WvOdKh/HDlHA== Content-Class: urn:content-classes:message X-MimeOLE: Produced By Microsoft MimeOLE V6.00.2600.0000 X-OriginalArrivalTime: 19 May 2003 18:27:02.0053 (UTC) FILETIME=[3DCDB550:01C31E34] testreplyreply6

  5. System.IO Namespace • Directory • File • StreamReader • StreamWriter • StringReader • StringWriter

  6. Stream • A stream is an abstraction of a sequence of bytes, such as a file, an input/output device, an inter-process communication pipe, or a TCP/IP socket. The Stream class and its derived classes provide a generic view of these different types of input and output, isolating the programmer from the specific details of the operating system and the underlying devices.

  7. Creating a Sequential Text File • Declare a System.IO.StreamWriter writer object: • Dim myFile As System.IO.StreamWriter • Create a file using System.IO.File.CreateText or AppendText method. • myFile=system.IO.File.CreateText(“c:\myTextFile.txt”) • CreateText method returns a StreamWriter. • If myTextFile.txt already exist, its contents will be erased • myFile=system.IO.File. AppendText(“c:\myTextFile.txt”) • If myTextFile.txt already exist, data will be appended to the end. • Note: CreateText and AppendText return a StreamWriter object. • Use writer object’s WriteLine method to write data. • myFile.WriteLine(“test”) ***create a new line • myFile.Write(“test”) ***does not create a new line • Use writer object’s Close method to close the file. • myFile.Close()

  8. Creating a Text File Imports System.IO Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click Dim myFile As System.IO.StreamWriter myFile = System.IO.File.CreateText("c:\myTextFile.txt") myFile.Write(TextBox1.Text) myFile.Close() End Sub

  9. Reading Files with StreamReader • Declare a System.IO.StreamReader reader object: • Dim myFile As System.IO.StreamReader • Open the file using System.IO.File.OpenText method. • myFile=system.IO.File.OpenText(“c:\myTextFile.txt”) • Use system.IO.File.Exists(FileName) to test if file exists. • Read Data • myFile.ReadLine() *** Read one line • myFile.Read() *** Read one character code. Use Chr function to convert the code to character: chr(myFile.Read()) • ReadLine and Read methods automatically move the pointer. • To detect the end of a file: MyFile.Peek=-1 • myFile.ReadToEnd() *** read entire contents of a file. • Use writer object’s Close method to close the file. • myFile.Close()

  10. Reading a Text File Private Sub Button2_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button2.Click Dim myFile As System.IO.StreamReader myFile = System.IO.File.OpenText("c:\myTextFile.txt") TextBox1.Text = myFile.ReadToEnd() myFile.Close() End Sub

  11. OpenFileDialog • Properties • Filter: description|filter • The description and the filter are separated with the pipe | symbol. • Text file (*.txt) | *.txt • All files (*.*) | *.* • Initial directory • FileName • Method: • ShowDialog

  12. OpenFileDialog Example If OpenFileDialog1.ShowDialog() = DialogResult.OK Then MessageBox.Show(OpenFileDialog1.FileName) myFile = System.IO.File.OpenText(OpenFileDialog1.FileName) TextBox1.Text = myFile.ReadToEnd Else MsgBox("no file selected") End If

  13. SaveFileDialog Example Dim outFile As System.IO.StreamWriter If documentName = "" Then If saveFileDialog1.ShowDialog = DialogResult.OK Then documentName = saveFileDialog1.FileName End If End If outFile = System.IO.File.CreateText(documentName) outFile.Write(TextBox1.Text) outFile.Close()

  14. DrawString: Print One Line of Text • System.Drawing.Graphics • DrawString method arguments: • String to print • Font • Brush • X position • Y position • The X, Y coordinates must be declared as Single data type. X coordinate is the horizontal distance across a line from the left edge, Y coordinate is the distance from the top.

  15. PrintDocument Control • PrinterSetting property: • PrinterName • PrintToFile • MaximumPage • MinimumPage • PaperSize • Method: • Print *** The Print method will trigger the PrintPage event

  16. PrintDialog Control • Use the PrintDialog to get the values for the PrinterSetting property of the PrintDocument control. • PrintDialog1.Document = PrintDocument1 • PrintDialog1.ShowDialog() • With PrintDocument1.PrinterSettings • .PrintToFile = PrintDialog1.PrinterSettings.PrintToFile • .MaximumPage = PrintDialog1.PrinterSettings.MaximumPage • .PrinterName = PrintDialog1.PrinterSettings.PrinterName • End With • Note: The PrintDialog’s Document property gets or sets a value indicating the PrintDocument used to obtain PrinterSetting.

  17. PrintDocument Example PrintDocument1.Print() Private Sub PrintDocument1_PrintPage(ByVal sender As System.Object, ByVal e As System.Drawing.Printing.PrintPageEventArgs) Handles PrintDocument1.PrintPage e.Graphics.DrawString(textbox1.text, New Font("courier", 18, FontStyle.Bold), Brushes.Black, 150, 80) End Sub

  18. Print and PrintPage Event • The Print method of the PrintDocument control will trigger the PrintPage event. This event is fired once for each page to be printed. After finishing printing one page, we can use the PrintPageEventArgs’ HasMorePage property to inform the PrintDocument whether there is more page to print.

  19. PrintPreviewDialog Control • PrintPreviewDialog1.Document = PrintDocument1 • PrintPreviewDialog1.ShowDialog()

  20. Print Multiple Lines • Textbox’s MultiLine property is true. • Textbox’s Lines property returns a string array with each line as an element. • The Y position must be increased by the height of the font.

  21. PrintPageEventArgs • DrawString: Send a line of text to the graphics page. • Properties: • MarginBounds.Left, top, bottom, etc. • HasMorePage

  22. Private Sub PrintDocument1_PrintPage(ByVal sender As System.Object, ByVal e As System.Drawing.Printing.PrintPageEventArgs) Handles PrintDocument1.PrintPage Dim fntPrintFont As New Font("Courier", 18) Dim sngLineHeight As Single = fntPrintFont.GetHeight + 2 Dim sngXPos As Single = e.MarginBounds.Left Dim sngYPos As Single = e.MarginBounds.Top Dim tempArray() As String tempArray = TextBox1.Lines Dim line As Integer For line = 0 To tempArray.GetUpperBound(0) e.Graphics.DrawString(tempArray(line), fntPrintFont, Brushes.Black, sngXPos, sngYPos) sngYPos += sngLineHeight Next End Sub

  23. Printing Multiple Pages Private Sub PrintDocument1_PrintPage(ByVal sender As System.Object, ByVal e As System.Drawing.Printing.PrintPageEventArgs) Handles PrintDocument1.PrintPage Static pageCount As Integer = 1 Static lineCount As Integer = 0 Dim fntPrintFont As New Font("Courier", 18) Dim sngLineHeight As Single = fntPrintFont.GetHeight + 2 Dim sngXPos As Single = e.MarginBounds.Left Dim sngYPos As Single = e.MarginBounds.Top Dim counter As Integer Dim tempArray() As String tempArray = TextBox1.Lines e.Graphics.DrawString("Page " & pageCount.ToString, fntPrintFont, Brushes.Black, sngXPos, sngYPos) sngYPos += sngLineHeight For counter = lineCount To tempArray.GetUpperBound(0) e.Graphics.DrawString(tempArray(counter), fntPrintFont, Brushes.Black, sngXPos, sngYPos) sngYPos += sngLineHeight If sngYPos >= e.MarginBounds.Bottom Then pageCount = pageCount + 1 lineCount = counter + 1 e.HasMorePages = True Exit For End If Next End Sub

  24. A Few Notes • The X, Y coordinates must be declared as Single data type. X coordinate is the horizontal distance across a line from the left edge, Y coordinate is the distance from the top. • Font object type and its properties and methods. • Textbox’s Lines property returns a string array with each line as an element. • Why the pageCount and lineCount are declared as Static?

  25. Comma-Delimited File • It stores each data item with a comma separating each item and places double quotes around string fields. • “S5”, ”Peter”, 3.0 • “S1”, “Paul”, 2.5

  26. Creating a Comma-Delimted File • Imports System.IO • Open the file for output: • fileNumber = FreeFile() • FileOpen(fileNumber, "c:\stdata.txt", OpenMode.Output) • Note: FreeFile function returns a file number. • Use WriteLine function to write a record to the file: • WriteLine(fileNumber, TextBox1.Text, TextBox2.Text, CDbl(TextBox3.Text)) • Note: Assuming write a student record with CID, CNAme, and GPA fields. • Use the FileCose function to close the file: • FileClose(fileNumber) • Note: OpenMode.Append

  27. Reading a Comma-Delimted File • Imports System.IO • Open the file for input: • fileNumber = FreeFile() • FileOpen(fileNumber, "c:\stdata.txt", OpenMode.Input) • Use Input function to read a field from the file: • If Not EOF(fileNumber) Then • Input(fileNumber, TextBox1.Text) • Input(fileNumber, TextBox2.Text) • Input(fileNumber, TextBox3.Text) • Else • MsgBox("Reach EOF") • End If • Note: The Input function can read only one filed from the file at a time. • Note: The EOF function detects the End of File condition. • Use the FileCose function to close the file: • FileClose(fileNumber)

  28. Sequentialy Accessing the Student File to Compute Average GPA Dim fileNumber, stCounter As Integer Dim temp1, temp2 As String Dim gpa, sumGpa As Double fileNumber = FreeFile() FileOpen(fileNumber, "c:\stdata.txt", OpenMode.Input) Do While Not EOF(fileNumber) Input(fileNumber, temp1) Input(fileNumber, temp2) Input(fileNumber, gpa) sumGpa += gpa stCounter += 1 Loop MessageBox.Show(sumGpa / stCounter.ToString)

  29. Create a File Processing Application • Use a form to display a customer record in textboxes. This form has a MoveNext button to show the next record. • A form to enter new customer data.

  30. Structures • A user-defined data type to hold related fields. • Structure emp • Dim eid As String • Dim ename As String • Dim salary As Double • End Structure • Dim myEmp as emp • myEmp.eid=“e1” • myEmp.ename=“peter” • myEmp.salary=5000.00

  31. A structure may contain arrays as fields, but cannot be declared with an initial size. Must use a ReDim statement to declare the size. Structure emp • Dim eid As String • Dim ename As String • Dim salary As Double • Dim dependent() As String • End Structure • Dim myEmp as emp • ReDim myEmp.dependent(3)

  32. A structure may also contain methods. • Structure emp • Dim eid As String • Dim ename As String • Dim salary As Double • Dim dependent() As String • Function tax(ByVal salary) As Double • tax = salary * 0.15 • End Function • End Structure • Dim myEmp As emp • myEmp.salary = 1000 • myEmp.tax(myEmp.salary)

  33. Random-Access File • Records in a random-access file do not have to processed in sequence. A record can be retrieved selectively. • A random-access file can be opened for both reading and writing. • Each record in a random-a ccess file is identified by a unique integer, the first record is record 1. • The records in a random-access file must be the same size.

  34. Using a Structure to Create Record • Structure emp • <VBFixedString(3)> Dim eid As String • <VBFixedString(10)> Dim ename As String • Dim salary As Double • Function tax(ByVal salary) As Double • tax = salary * 0.15 • End Function • End Structure • Note: Use <VBFixedString(3)> to control string size.

  35. Opening a Random-Access File • FileOpen(fileNumber, fileName,OpenMode,OpenAccess, OpenShare, RecordLength) • OpenMode: Random • OpenAccess:ReadWrite • OpenShare • RecordLength • Example: • Dim MyEmp as Emp • fileNumber = FreeFile() • FileOpen(fileNumber, "c:\empRnd.txt", OpenMode.Random, OpenAccess.ReadWrite, OpenShare.Default, Len(myEmp))

  36. Writing a Record • FilePut(FileNumber, Record, RecordNumber) • myEmp.eid = TextBox1.Text • myEmp.ename = TextBox2.Text • myEmp.salary = CDbl(TextBox3.Text) • FilePut(fileNumber, myEmp, CInt(myEmp.eid.Substring(1))) Note: Assuming EID is of this format: XNN.

  37. Reading a Record • FileGet(FileNumber, Record, RecordNumber) • Dim recNumber As Integer • recNumber = CInt(InputBox("Please enter empID: ").Substring(1)) • FileGet(fileNumber, myEmp, recNumber) • TextBox1.Text = myEmp.eid • TextBox2.Text = myEmp.ename • TextBox3.Text = myEmp.salary.ToString

  38. Random File Example Dim fileNumber As Integer Structure emp <VBFixedString(3)> Dim eid As String <VBFixedString(10)> Dim ename As String Dim salary As Double Function tax(ByVal salary) As Double tax = salary * 0.15 End Function End Structure Dim myEmp As emp Private Sub Form2_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load fileNumber = FreeFile() FileOpen(fileNumber, "c:\empRnd.txt", OpenMode.Random, OpenAccess.ReadWrite, OpenShare.Default, Len(myEmp))

  39. Writing and Reading Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click myEmp.eid = TextBox1.Text myEmp.ename = TextBox2.Text myEmp.salary = CDbl(TextBox3.Text) FilePut(fileNumber, myEmp, CInt(myEmp.eid.Substring(1))) End Sub Private Sub Button2_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button2.Click Dim recNumber As Integer recNumber = CInt(InputBox("Please enter empID: ").Substring(1)) FileGet(fileNumber, myEmp, recNumber) If myEmp.eid.Substring(0, 1) <> "e" Then MsgBox("record not exist") Else TextBox1.Text = myEmp.eid TextBox2.Text = myEmp.ename TextBox3.Text = myEmp.salary.ToString End If End Sub

  40. Sequential Access to a Random-Access File Dim outString As String Dim recNumber As Integer = 1 Do While Not EOF(fileNumber) FileGet(fileNumber, myEmp, recNumber) outString = outString & recNumber.ToString & myEmp.eid & myEmp.ename & myEmp.salary.ToString & vbCrLf recNumber += 1 Loop MessageBox.Show(outString) Note: Do While recNumber <= NumberOfRecords

  41. Hashing • RecordAddress = H(Key) • H(Key)=Key Mod M 0 <= Key Mod M <= M – 1 1 <= 1 + Key Mod M <= M

  42. Hashing Example • Key Mod 8 • H(1821) = 5 • H(7115) = 3 • H(2428) = 4 • H(4750) = 6 • H(1620) = 4 **** Collision • H(4692) = 4 • H(4758) = 6 • Collision resolution: • Linear probing

  43. Inserting a Record • H(Key) • If space H(Key) available, insert into space K(Key) • Else check subsequent space until a free space is found. • *** How to detect the file is full?

  44. Searching a Record • Read record at H(Key) • If no record at H(Key), then record not exist • If record at H(Key) is the searched record, then Found • Else Search the next space until reach an empty space.

  45. Deleting a Record • Search the record to be deleted. • Change a field to a special deletion flag. • Write it back to its original space with the deletion flag.

  46. Serialization • The act of saving (serializing) an object onto a storage medium and later deserializing it from the storage medium to recreate an object. • BinaryFormatter: • Serialize • Deserialize

  47. Imports System.IO Imports System.Runtime.Serialization.Formatters.Binary Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load Dim fs As New FileStream("c:\testSerializing.dat", FileMode.Create) Dim myArrayList As New ArrayList myArrayList.Add("A") myArrayList.Add("B") myArrayList.Add(5) myArrayList.Add(10) Dim bf As New BinaryFormatter bf.Serialize(fs, myArrayList) fs.Close() End Sub Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click Dim fs As New FileStream("c:\testSerializing.dat", FileMode.Open) Dim myArrayList As New ArrayList Dim bf As New BinaryFormatter myArrayList = CType(bf.Deserialize(fs), ArrayList) Dim obj As New Object For Each obj In myArrayList ListBox1.Items.Add(obj) Next End Sub

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