ODBC Example for Visual Basic

Take the following steps to create and use a simple ODBC database, containing only images. (For a more sophisticated approach, refer to Using ODBC to Access Image Data.)

Note:

The LEADTOOLS COM requires ODBC drivers that can properly handle long binary fields. Examples have been tested and will work with version 3.0 of the Microsoft ODBC Desktop Driver Pack. (This driver pack ships with Access 95 and works on 32-bit systems.) You can download drivers from the LEAD BBS, the CompuServe forum, or the Worldwide Web home page. The CompuServe forum is at GO LEADTECH. The web page is ftp://ftp.leadtools.com/pub/utils/ODBC32.zip. The file to download is ODBC32.ZIP.

1.	Make a copy of the project that you created in Loading and Displaying an Image; then load the copied project.
2.	In the Add-Ins menu, select the Data Manager...
3.	In the Data Manager Window's File menu, select New, and create an Access database named c:\lead\lead.mdb.
4.	Click the New button, and create a table with one field as follows:
	Name:	ltvbpic
	Field Name:	photo
	Data Type:	long binary
5.	Add the following LEAD Raster objects to your project,
	a. LEADRasterODBC Object Library.
		For VB4: On the Tools pull-down menu, use the References option, and select the LEAD Raster ODBC Object Library (14.5).
		For VB5: On the Project pull-down menu, use the References option, and select the LEAD Raster ODBC Object Library (14.5).
	b. LEADRasterProcess Object Library.
		For VB4: On the Tools pull-down menu, use the References option, and select the LEAD RasterProcess Object Library (14.5).
		For VB5: On the Project pull-down menu, use the References option, and select the LEAD RasterProcess Object Library (14.5).
6.	Add the following statment to your public section:

Public RasterODBC As New LEADRasterODBC

7.	Exit the Data Manager.
8.	Open the ODBC administrator and click the Add button.
9.	Select Microsoft Access driver and click the OK button.
10.	Enter the name LEADACCESS.
11.	Click the Select directory button and select the LEAD directory.
12.	Click the OK button; click the next OK button; then click the Close button.
13.	In Visual Basic, replace the code in the main form's init procedure as follows:

  'Position and size the main form so that it takes up most of the screen.
  Width = Screen.Width * 0.9
  Height = Screen.Height * 0.8
  Left = (Screen.Width - Width) / 2
  Top = (Screen.Height - Height) / 2
  ' Set the position and size of the LEAD control.
  ' Allow for a border of 1/8 of the form size.
  ' The units of measure do not matter, since we are calculating proportions.
  HeightAllowed = ScaleHeight * 3 / 4
  WidthAllowed = ScaleWidth * 3 / 4
  LEADRasterView1.Left = (ScaleWidth - WidthAllowed) / 2
  LEADRasterView1.Top = (ScaleHeight - HeightAllowed) / 2
  LEADRasterView1.Width = WidthAllowed
  LEADRasterView1.Height = HeightAllowed
  'Turn off automatic repainting and turn on scroll bars.
  LEADRasterView1.AutoRepaint = False
  LEADRasterView1.AutoScroll = True
  'Set the image display size to match the LEADRasterView control
  LEADRasterView1.SetDstRect 0, 0, LEADRasterView1.ScaleWidth, LEADRasterView1.ScaleHeight
  LEADRasterView1.SetDstClipRect 0, 0, LEADRasterView1.ScaleWidth, LEADRasterView1.ScaleHeight
  ' Open the database.
  RasterODBC.Raster = LEADRasterView1.Raster
  DString = "ODBC;DSN=LEADACCESS"
  RasterODBC.dbOpen DString, "ltvbpic", "photo", DB_OPENOPTIONS_NONE
  RasterODBC.dbLoadBits = 24
  RasterODBC.dbLockingMode = DB_LOCKINGMODE_OPTIMISTIC
  LEADRasterView1.ForceRepaint
  If RasterODBC.dbIsBOF = True And RasterODBC.dbIsEOF = True Then
    msg = "The database is empty."
    answer = MsgBox(msg, 0, "Notice")
    NextRec.Enabled = False
    PrevRec.Enabled = False
  End If

14.	Add a common dialog control to your main form and name it Commdlg.
15.	At the top of your main form, add seven command buttons and name them as follows: Add, Update, Delete, FirstRec, NextRec, PrevRec, and LastRec.
16.	For the Add button, add the following code to the click procedure:

Dim RasterIO As New LEADRasterIO
If RasterODBC.dbCanAppend = False Then
    msg = "You cannot add to this database."
    answer = MsgBox(msg, 0, "Error")
Else
    RasterODBC.dbAddNew
    CommDlg.Filter = "All Files|*.*"
    CommDlg.Flags = cdlOFNFileMustExist
    CommDlg.DialogTitle = "Open File"
    CommDlg.CancelError = True
    CommDlg.ShowOpen
    filename = CommDlg.filename
    RasterIO.Load LEADRasterView1.Raster, filename, 0, 0, 1
    RasterODBC.Raster = LEADRasterView1.Raster
    nret = RasterODBC.dbUpdate(FILE_CMP, 0, QFACTOR_QMS)
        If nret <> 0 Then
            msg = "You cannot update this database."
            answer = MsgBox(msg, 0, "Error")
        Else
            RasterODBC.dbMoveLast
            LEADRasterView1.ForceRepaint
            msg = "Image added to the database."
            answer = MsgBox(msg, 0, "LEAD")
            NextRec.Enabled = True
            PrevRec.Enabled = True
            If RasterODBC.dbIsBOF = True Then
              PrevRec.Enabled = False
            Else
              PrevRec.Enabled = True
            End If
            If RasterODBC.dbIsEOF = True Then
              NextRec.Enabled = False
            Else
              NextRec.Enabled = True
            End If
    End If
End If

17.	For the Update button, add the following code to the click procedure:

Dim RasterProc As New LEADRasterProcess
If RasterODBC.dbCanUpdate = False Then
    msg = "You cannot update this database."
    answer = MsgBox(msg, 0, "Error")
ElseIf RasterODBC.dbIsBOF = True Or RasterODBC.dbIsEOF = True Then
    msg = "There is no current record."
    answer = MsgBox(msg, 0, "Error")
Else
    If RasterODBC.dbEditMode = DB_EDITMODE_NONE Then
        RasterODBC.dbEdit
        RasterProc.Flip LEADRasterView1.Raster
        LEADRasterView1.ForceRepaint
    End If
    RasterODBC.dbUpdate FILE_CMP, 0, QFACTOR_QMS
End If

18.	For the Delete button, add the following code to the click procedure:

If RasterODBC.dbCanUpdate = False Then
    msg = "You cannot update this database."
    answer = MsgBox(msg, 0, "Error")
ElseIf RasterODBC.dbIsBOF = True Or RasterODBC.dbIsEOF = True Then
    msg = "There is no current record."
    answer = MsgBox(msg, 0, "Error")
Else
    RasterODBC.dbDelete
    RasterODBC.dbRequery
    RasterODBC.dbMoveFirst
    If RasterODBC.dbIsBOF = True And RasterODBC.dbIsEOF = True Then
      NextRec.Enabled = False
      PrevRec.Enabled = False
    End If
    LEADRasterView1.ForceRepaint
End If

19.	For the First button, add the following code to the click procedure:

If RasterODBC.dbIsBOF = True And RasterODBC.dbIsEOF = True Then
    msg = "The database is empty."
    answer = MsgBox(msg, 0, "Notice")
    NextRec.Enabled = False
    PrevRec.Enabled = False
Else
    RasterODBC.dbMoveFirst
    PrevRec.Enabled = False
    NextRec.Enabled = True
    LEADRasterView1.ForceRepaint
End If

20.	For the Next button, add the following code to the click procedure:

If RasterODBC.dbIsBOF = True And RasterODBC.dbIsEOF = True Then
    PrevRec.Enabled = False
    NextRec.Enabled = False
    msg = "The database is empty."
    answer = MsgBox(msg, 0, "Notice")
Else
      RasterODBC.dbMoveNext
      If RasterODBC.dbIsEOF = True Then
        NextRec.Enabled = False
        RasterODBC.dbMovePrev
        msg = "Already at last record."
        answer = MsgBox(msg, 0, "Notice")
      Else
        PrevRec.Enabled = True
      End If
      LEADRasterView1.ForceRepaint
End If

21.	For the Prev button, add the following code to the click procedure:

If RasterODBC.dbIsBOF = True And RasterODBC.dbIsEOF = True Then
    PrevRec.Enabled = False
    NextRec.Enabled = False
    msg = "The database is empty."
    answer = MsgBox(msg, 0, "Notice")
Else
      RasterODBC.dbMovePrev
      If RasterODBC.dbIsBOF = True Then
         PrevRec.Enabled = False
         RasterODBC.dbMoveNext
         msg = "Already at first record."
         answer = MsgBox(msg, 0, "Notice")
      Else
         NextRec.Enabled = True
      End If
      LEADRasterView1.ForceRepaint
End If

22.	For the Last button, add the following code to the click procedure:

If RasterODBC.dbIsBOF = True And RasterODBC.dbIsEOF = True Then
    msg = "The database is empty."
    answer = MsgBox(msg, 0, "Notice")
    NextRec.Enabled = False
    PrevRec.Enabled = False
Else
    RasterODBC.dbMoveLast
    NextRec.Enabled = False
    PrevRec.Enabled = True
    LEADRasterView1.ForceRepaint
End If

23.	Update the main form's unload procedure as follows:

Private Sub Form_Unload(Cancel As Integer)
RasterODBC.dbClose
End Sub

24.	Run your program to test it.