Data files and databases

Need a control to browse to a file Standard controls for drive folder and list not much use The CommonDialogs control offers –drive folder file browse to select file –print –font select –colour select But you need to add it in..

Adding components

Using the Common Dialog Control Private Sub Command1_Click() CommonDialog1.ShowOpen MsgBox ("You selected " & CommonDialog1.FileName).. code to process FileName End Sub

File open exercise Program to browse and display graphics files Use a common dialog control to select graphics files Set the filter of the dialog to something like: Image files | *.bmp; *.jpg; *.jpeg | All files | *.* Display the selected image in a Picture control (see graphics)

VB data file ideas 2 modes – sequential (work through file start to end - character (external format)) random (can move back and forth through file, binary (internal format) )

Sequential – write # and input# Open "c:\walter\vb\filing\test1.dat" For Output As #1 Write #1, 1, 2, 3.1, "Test1", "Test2" Close #1 Open "c:\walter\vb\filing\test1.dat" For Input As #1 Input #1, x, y, z, a, b Close #1

Sequential – Print # and Line Input# Open "c:\walter\vb\filing\test1.dat" For Output As #1 Print #1, 1, 2, "Test1" Close #1 Open "c:\walter\vb\filing\test1.dat" For Input As #1 Line Input #1, x Close #1 MsgBox (x)

Exercise – sequential filing 1.Fill an array with 100 random integers 2.Save them into a file ( write# ) 3.Read file back ( input# ) into a second array 4.Check arrays have same content

Random Data in file as records Must define size of record (fixed length good) Can then seek to nth record And read or write it

User-defined type (record) Private Type myRecord payroll As Integer department As Integer name As String * 14 End Type fixed length string length of record = = 18 bytes

Writing to random access file Dim emp As myRecord emp.payroll = 23 emp.department = 3 emp.name = "Fred" Open "c:\walter\vb\filing\test.dat" For Random As #1 Len = 18 Put #1, 1, emp emp.payroll = 17 emp.department = 6 emp.name = "John" Put #1, 2, emp Put #1, 3, emp Close #1 result on next slide record position 1

Random file contents record 1 record 2 record 3 2 bytes = integer = 23 2 bytes = 1 integer = 3 string padded with spaces to length 14

Reading Random File Dim emp As myRecord Open "c:\walter\vb\filing\test.dat" For Random As #1 Len = 18 Get #1, 2, emp Close #1 MsgBox (emp.payroll & " " & emp.department & " " &_ emp.name) read second record

Binary = random with record size 1 Dim b As Byte Open "c:\walter\vb\filing\test.dat" For Binary As #1 For bytePosition = 1 To 10 Get #1, bytePosition, b Debug.Print b Next Close #1

Exercise – data file Using binary mode, write the characters A to Z into a file (ASCII 65 on) Then read them back in reverse ie byte position 26 first Debug.print them out

Working with a database – the hard way

Private Sub Command1_Click() Data1.Recordset.Delete Data1.Refresh End Sub

Working with a database – the wizard Addins..Addin Manager

Working with a database – the wizard

Exercise – database access Use Access to produce a simple database with just one table – personnel = ID name and department number (Access97 format) In a VB project have two forms –one with a data control, hand-coded (explore insert delete buttons) –one created by the Data Form Wizard