The information in this article applies to:
- Professional Edition of Microsoft Visual Basic for Windows, version 3.0
SYMPTOMS
If you try to bind a picture control to a Microsoft Access database field
that contains an OLE object such as a PaintBrush bitmap, you will
correctly receive the error "Invalid picture."
CAUSE
This error occurs because the picture control can only bind to a bitmap,
metafile, or icon stored in the database field -- not to an OLE object.
RESOLUTION
Using the method described below, you can simulate the binding of a picture
control to a PaintBrush OLE (or bitmap) object.
MORE INFORMATION
If you use Microsoft Access to store a PaintBrush picture in an OLE
field, there is no way to bind any control provided with Visual Basic
version 3.0 to the OLE field. Ideally you could bind the MSOLE2
control to the data control, but no features were added to the MSOLE2
control to allow you to bind to a database field.
From Visual Basic, you can use a bound picture control to store and
retrieve bitmaps, metafiles, and icons directly in a long binary or OLE
database field. However, Microsoft Access will not be able to display
the bitmap, metafile, or icon that you've stored.
Step-by-Step Example
The following example demonstrate how you can create an application that
retrieves and displays a bitmap from an OLE field containing a PaintBrush
object. To get it to work, you need to have the NWIND.MDB sample database
provided with Microsoft Access.
- Start Visual Basic or from the File menu, choose New Project (ALT, F, N)
if Visual Basic is already running. Form1 is created by default.
- From the File menu, choose New Module (ALT, F, M). Module1 is created.
- Add a picture control (Picture1) to Form1.
- Add a data control (Data1) to Form1.
- Set the Data1.Databasename property to NWIND.MDB and include the full
path to this file. This file is a sample database that ships with
Microsoft Access versions 1.0 and 1.1. Look for it in your Microsoft
Access directory -- for example, C:\ACCESS.
- Set the Data1.RecordSource property to Employees.
- Add the following code to the Data1_Reposition event procedure in Form1:
'**********************************************************************
'* Title
'* Data1_Reposition ()
'*
'* Description
'* Each time the data control is being repositioned to a new
'* record, the bitmap contained in the "Photo" is displayed
'* in Picture1. Therefore, it simulates binding the picture
'* control to an OLE field containing a Microsoft Paint Brush
'* picture object.
'*
'* The code requires a field named Photo, and it requires that
'* the embedded OLE object be a Microsoft Paint Brush picture.
'**********************************************************************
Sub Data1_Reposition ()
Screen.MousePointer = 11
'Make sure this is the current record:
If Not (Data1.Recordset.EOF And Data1.Recordset.BOF) Then
'Change Photo to the name of the OLE field
'for the record set you are using:
DisplayOleBitmap Picture1, Data1.Recordset("Photo")
End If
Screen.MousePointer = 0
End Sub
- Add the following code to Module1:
'**********************************************************************
'* OLEACCES.BAS
'*
'* general-declarations section
'**********************************************************************
Option Explicit
Global Const LENGTH_FOR_SIZE = 4
Global Const OBJECT_SIGNATURE = &H1C15
Global Const OBJECT_HEADER_SIZE = 20
Global Const CHECKSUM_SIGNATURE = &HFE05AD00
Global Const CHECKSUM_STRING_SIZE = 4
'PT : Window sizing information for object
' Used in OBJECTHEADER type
Type PT
Width As Integer
Height As Integer
End Type
'OBJECTHEADER : Contains relevant information about object
'
Type OBJECTHEADER
Signature As Integer 'Type signature (0x1c15)
HeaderSize As Integer 'Size of header (sizeof(struct
'OBJECTHEADER) + cchName +
'cchClass)
ObjectType As Long 'OLE Object type code (OT_STATIC,
'OT_LINKED, OT_EMBEDDED)
NameLen As Integer 'Count of characters in object
'name (CchSz(szName) + 1)
ClassLen As Integer 'Count of characters in class
'name (CchSz(szClass) + 1)
NameOffset As Integer 'Offset of object name in
'structure (sizeof(OBJECTHEADER))
ClassOffset As Integer 'Offset of class name in
'structure (ibName + cchName)
ObjectSize As PT 'Original size of object (see
'code below for value)
OleInfo As String * 256
End Type
Type OLEHEADER
OleVersion As Long
Format As Long
OleInfo As String * 512
End Type
'Enter the following Declare statement as one, single line:
Declare Function GetTempFileName Lib "Kernel" (ByVal cDriveLetter
As Integer, ByVal lpPrefixString As String, ByVal wUnique As
Integer, ByVal lpTempFileName As String) As Integer
'Enter the following Declare statement as one, single line:
Declare Sub hmemcpy Lib "Kernel" (dest As Any, source As Any,
ByVal bytes As Long)
'**********************************************************************
'* Title
'* DisplayOleBitmap
'*
'* Description
'* Causes the OLE bitmap in the given data field to be
'* copied to a temporary file. The bitmap is then
'* displayed in the given picture.
'*
'* Parameters
'* ctlPict Picture control in which to display the
'* bitmap image
'* OleField Database field containing the OLE
'* embedded Microsoft Paint Brush bitmap
'**********************************************************************
Sub DisplayOleBitmap (ctlPict As Control, OleField As Field)
Const DT_LONGBINARY = 11
Dim r As Integer
Dim Handle As Integer
Dim OleFileName As String
If OleField.Type = DT_LONGBINARY Then
OleFileName = CopyOleBitmapToFile(OleField)
If OleFileName <> "" Then
'Display the bitmap:
ctlPict.Picture = LoadPicture(OleFileName)
'Delete the temporary file:
Kill OleFileName
End If
End If
End Sub
'**********************************************************************
'* Title
'* CopyOleBitmapToFile
'*
'* Description
'* Copies the bitmap contained in a OLE field to a file.
'**********************************************************************
Function CopyOleBitmapToFile (OleField As Field) As String
Const BUFFER_SIZE = 8192
Dim tempFileName As String
Dim Handle As Integer
Dim Buffer As String
Dim BytesNeeded As Long
Dim Buffers As Long
Dim Remainder As Long
Dim ObjHeader As OBJECTHEADER
Dim sOleHeader As String
Dim ObjectOffset As Long
Dim BitmapOffset As Long
Dim BitmapHeaderOffset As Integer
Dim r As Integer
Dim i As Long
tempFileName = ""
If OleField.FieldSize() > OBJECT_HEADER_SIZE Then
'Get the Microsoft Access OLE header:
sOleHeader = OleField.GetChunk(0, OBJECT_HEADER_SIZE)
hmemcpy ObjHeader, ByVal sOleHeader, OBJECT_HEADER_SIZE
'Calculate the offset where the OLE object starts:
ObjectOffset = ObjHeader.HeaderSize + 1
'Get enough bytes after the OLE header so that we get the
'bitmap header
Buffer = OleField.GetChunk(ObjectOffset, 512)
'Make sure the class of the object is a Paint Brush object
If Mid(Buffer, 12, 6) = "PBrush" Then
BitmapHeaderOffset = InStr(Buffer, "BM")
If BitmapHeaderOffset > 0 Then
'Calculate the beginning of the bitmap:
BitmapOffset = ObjectOffset + BitmapHeaderOffset -1
'Calculate the size of the bitmap:
'Enter the following BytesNeeded statement as a single line:
BytesNeeded = OleField.FieldSize() - OBJECT_HEADER_SIZE -
BitmapHeaderOffset - CHECKSUM_STRING_SIZE + 1
'Calculate the number of buffers needed to copy
'the OLE object based on the bitmap size:
Buffers = BytesNeeded \ BUFFER_SIZE
Remainder = BytesNeeded Mod BUFFER_SIZE
'Get a unique, temp filename:
tempFileName = Space(255)
r = GetTempFileName(0, "", -1, tempFileName)
'Copy the bitmap to the temporary file chunk by chunk:
Handle = FreeFile
Open tempFileName For Binary As #Handle
For i = 0 To Buffers - 1
'Enter the following Buffer statement as a single line:
Buffer = OleField.GetChunk(BitmapOffset + i *
BUFFER_SIZE, BUFFER_SIZE)
Put #Handle, , Buffer
Next
'Copy the remaining chunk of the bitmap to the file:
'Enter the following Buffer statement as a single line:
Buffer = OleField.GetChunk(BitmapOffset + Buffers *
BUFFER_SIZE, Remainder)
Put #Handle, , Buffer
Close #Handle
End If
End If
End If
CopyOleBitmapToFile = Trim(tempFileName)
End Function
- From the Run menu, choose Start (ALT, R, S) or press the F5 key to run
the program.
You should see the photo of the first employee displayed in the picture
box. By clicking the directional arrows on the data control, you can view
the other employee photos.
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