Visual Basic Concepts

Article
01/04/2007

Creating the MyOSPObject Class

In the previous topic, we added an ActiveX DLL project to the AXData sample. In this step, we'll create a class that implements the OLE DB Simple Provider (OSP) interfaces to access data stored in a text file.

Note This topic is part of a series that walks you through creating sample data source components. It begins with the topic Creating Data Sources.

To create the MyOSPObject class

In the Project Explorer, select Class1 from the MyDataComponent project. In the Properties window, set the properties for Class1 as follows:

Property	Setting
(Name)	MyOSPObject

You may have noticed that the DataSourceBehavior is set to none. If this component is to act as a data source, shouldn't the DataSourceBehavior be set to another value? Don't worry — we'll add another class in a later step that provides the data source capability for the component.

Double-click MyOSPObject in the Project Explorer to open its code window.
In the Object box, select (General). In the Procedure box, select (Declarations) to position yourself at the top of the code module. Add the following code:
```
Option Explicit
Implements OLEDBSimpleProvider
Dim MyOSPArray()
Dim RowCount As Integer
Dim ColCount As Integer
Dim colListeners As New Collection
Dim ospl As OLEDBSimpleProviderListener
Public FilePath As String
```
Note the use of the Implements keyword for OLEDBSimpleProvider. Remember, Implements is like a contract — it means that you'll need to implement all of the interfaces of the OLEDBSimpleProvider class.

Add the following procedures to read and write data from a file:

Public Sub LoadData()
   ' This procedure loads data from a semi-colon
   ' delimited file into an array.
   Dim GetLine As Variant
   Dim Spot As Integer, Position As Integer
   Dim Row As Integer, Col As Integer

   On Error GoTo ErrorTrap
   Open FilePath For Input Lock Read Write As #1
   Position = 1
   Row = 0
   Line Input #1, GetLine
   Spot = InStr(1, GetLine, ";")
   RowCount = val(Left$(GetLine, Spot))
   ColCount = val(Right$(GetLine, Len(GetLine) - Spot))
   ReDim MyOSPArray(RowCount + 1, ColCount + 1)
   While Not EOF(1)
      Line Input #1, GetLine
      Col = 1
      Spot = InStr(1, GetLine, ";")
      While Spot <> 0
         MyOSPArray(Row, Col) = Left$(GetLine, Spot - 1)
         Col = Col + 1
         GetLine = Right$(GetLine, Len(GetLine) - Spot)
         Spot = InStr(1, GetLine, ";")
      Wend
      If Len(GetLine) <> 0 Then
         MyOSPArray(Row, Col) = GetLine
      End If
      Row = Row + 1
   Wend
   Close #1
   Exit Sub

ErrorTrap:
   Err.Raise (E_FAIL)
End Sub

Public Sub SaveData()
   ' This procedure writes data from an array to a semi-colon
   ' delimited file
   Dim PutLine As Variant
   Dim iRow As Integer, iCol As Integer

   On Error GoTo ErrorTrap
   Open FilePath For Output Lock Read Write As #1
   Print #1, RowCount & ";" & ColCount

   For iRow = 0 To RowCount
      For iCol = 1 To ColCount
         PutLine = PutLine & MyOSPArray(iRow, iCol) & ";"
      Next iCol
      Print #1, PutLine
      PutLine = ""
   Next iRow
   Close #1
   Exit Sub

ErrorTrap:
   Err.Raise (E_FAIL)
End Sub

In the Object box, select Class. In the Procedure box, select the Terminate event. Add the following code to the Class_Terminate event procedure to save the data when the class is terminated:
```
Private Sub Class_Terminate()
   On Error Resume Next
   ' Call the SaveData method
   SaveData
End Sub
```

To implement OLEDBSimpleProvider

Since the MyOSPObject class implements the OLEDBSimpleProvider class, we have to implement all of its interfaces, even if we aren't going to use them:

In the Object box, select OLEDBSimpleProvider. In the Procedure box, select the addOLEDBSimpleProviderListener function. Add the following code to the function procedure to add listeners that will notify the class when data changes:

Private Sub OLEDBSimpleProvider_addOLEDBSimpleProviderListener _
   (ByVal pospIListener As OLEDBSimpleProviderListener)
   ' Add a listener to the Listeners collection.
   If Not (pospIListener Is Nothing) Then
      Set ospl = pospIListener
      colListeners.Add ospl
   End If
End Sub

In the Object box, select OLEDBSimpleProvider. In the Procedure box, select the deleteRows function. Add the following code to the procedure to delete a row of data from a file:

Private Function OLEDBSimpleProvider_deleteRows _
   (ByVal iRow As Long, ByVal cRows As Long) As Long
   Dim TempArray()
   Dim listener As OLEDBSimpleProviderListener
   Dim v As Variant

   ' Make sure iRow is in the correct range:
   If iRow < 1 Or iRow > RowCount Then
      Err.Raise (E_FAIL)
   End If

   ' Set cRows to the actual number which can be deleted
   If iRow + cRows > RowCount + 1 Then
      cRows = RowCount - iRow + 1
   End If

   ' Establish a Temporary Array
   cNewRows = RowCount - cRows
   ReDim TempArray(cNewRows + 1, ColCount + 1)

   ' Notify each listener:
   For Each v In colListeners
      Set listener = v
      listener.aboutToDeleteRows iRow, cRows
   Next

   ' Copy over the first rows which are not being deleted
   For Row = 0 To iRow - 1
      For Col = 0 To ColCount
         TempArray(Row, Col) = MyOSPArray(Row, Col)
      Next Col
   Next Row

   ' Copy the last rows which are not being deleted
   For Row = iRow + cRows To RowCount
      For Col = 0 To ColCount
         TempArray(Row - cRows, Col) = MyOSPArray(Row, Col)
      Next Col
   Next Row

   ' Re-allocate the array to copy into it
   ReDim MyOSPArray(cNewRows + 1, ColCount + 1)

   ' Set the real row count back in
   RowCount = cNewRows

   ' Copy over the rows
   For Row = 0 To cNewRows
      For Col = 0 To ColCount
         MyOSPArray(Row, Col) = TempArray(Row, Col)
      Next Col
   Next Row

   ' Clear the temporary array
   ReDim TempArray(0)

   ' Notify each listener
   For Each v In colListeners
      Set listener = v
      listener.deletedRows iRow, cRows
   Next

   ' Return number of deleted rows
   OLEDBSimpleProvider_deleteRows = cRows
End Function

In the Object box, select OLEDBSimpleProvider. In the Procedure box, select the find function. Add the following code to the procedure to find data within a file:

Private Function OLEDBSimpleProvider_find(ByVal iRowStart As Long, _
   ByVal iColumn As Long, ByVal val As Variant, _
   ByVal findFlags As OSPFIND, ByVal compType As OSPCOMP) As Long

   Dim RowStart As Integer, RowStop As Integer
   If (findFlags And (OSPFIND_UP Or OSPFIND_UPCASESENSITIVE)) _
      <> 0 Then
      RowStart = RowCount + 1
      RowStop = 0
      StepValue = -1
   Else
      RowStart = 0
      RowStop = RowCount + 1
      StepValue = 1
   End If

   If (findFlags And (OSPFIND_CASESENSITIVE Or _
      OSPFIND_UPCASESENSITIVE)) <> 0 Then
      CaseSens = 1   'Use a Text Compare not Case Sensitive
   Else
      CaseSens = 0   'Not Case Sensitive use Binary Compare
   End If

   If VarType(val) = vbString Then
      StringComp = True
   Else
      StringComp = False
   End If

   iAnswerRow = -1
   For iRow = RowStart To RowStop Step StepValue
      If StringComp Then
         CompResult = StrComp(MyOSPArray(iRow, iColumn), _
            val, CaseSens)
         Select Case (compType)
            Case OSPCOMP_DEFAULT, OSPCOMP_EQ:
               If CompResult = 0 Then
                  iAnswerRow = iRow
                  Exit For
               End If
            Case OSPCOMP_GE
               If CompResult >= 0 Then
                  iAnswerRow = iRow
                  Exit For
               End If
            Case OSPCOMP_GT
               If CompResult > 0 Then
                  iAnswerRow = iRow
                  Exit For
               End If
            Case OSPCOMP_LE
               If CompResult <= 0 Then
                  iAnswerRow = iRow
                  Exit For
               End If
            Case OSPCOMP_LT
               If CompResult < 0 Then
                  iAnswerRow = iRow
                  Exit For
               End If
            Case OSPCOMP_NE
               If CompResult <> 0 Then
                  iAnswerRow = iRow
                  Exit For
               End If
         End Select
      Else
         Select Case (compType)
            Case OSPCOMP_DEFAULT, OSPCOMP_EQ:
               If MyOSPArray(iRow, iColumn) = val Then
                  iAnswerRow = iRow
                  Exit For
               End If
            Case OSPCOMP_GE
               If MyOSPArray(iRow, iColumn) >= val Then
                  iAnswerRow = iRow
                  Exit For
               End If
            Case OSPCOMP_GT
               If MyOSPArray(iRow, iColumn) > val Then
                  iAnswerRow = iRow
                  Exit For
               End If
            Case OSPCOMP_LE
               If MyOSPArray(iRow, iColumn) <= val Then
                  iAnswerRow = iRow
                  Exit For
               End If
            Case OSPCOMP_LT
               If MyOSPArray(iRow, iColumn) < val Then
                  iAnswerRow = iRow
                  Exit For
               End If
            Case OSPCOMP_NE
               If MyOSPArray(iRow, iColumn) <> val Then
                  iAnswerRow = iRow
                  Exit For
               End If
         End Select
      End If
   Next iRow
   OLEDBSimpleProvider_find = iAnswerRow
End Function

In the Object box, select OLEDBSimpleProvider. In the Procedure box, select the getColumnCount function. Add the following code to the procedure to return the number of fields within a file:
```
Private Function OLEDBSimpleProvider_getColumnCount() As Long
   OLEDBSimpleProvider_getColumnCount = ColCount
End Function
```
In the Object box, select OLEDBSimpleProvider. In the Procedure box, select the getEstimatedRows function. Add the following code to the procedure to return the estimated number of rows of data within a file:
```
Private Function OLEDBSimpleProvider_getEstimatedRows() As Long
   OLEDBSimpleProvider_getEstimatedRows = RowCount
End Function
```
In the Object box, select OLEDBSimpleProvider. In the Procedure box, select the getLocale function. Add the following code to the procedure:
```
Private Function OLEDBSimpleProvider_getLocale() As String
   OLEDBSimpleProvider_getLocale = ""
End Function
```
Note that in this case the function simply returns a null value. Even though it doesn't do anything, the function has to be added — since this class implements OLEDBSimpleProvider, all of its interfaces have to be included.
In the Object box, select OLEDBSimpleProvider. In the Procedure box, select the getRowCount function. Add the following code to the procedure to return the number of rows of data within a file:
```
Private Function OLEDBSimpleProvider_getRowCount() As Long
   OLEDBSimpleProvider_getRowCount = RowCount
End Function
```

In the Object box, select OLEDBSimpleProvider. In the Procedure box, select the getRWStatus function. Add the following code to the procedure to set the Read/Write status by column — in this case, the first column will be read-only while the remaining columns will be read-write:

Private Function OLEDBSimpleProvider_getRWStatus _
   (ByVal iRow As Long, ByVal iColumn As Long) As OSPRW
   If iColumn = 1 Then
      ' Make the first column read-only
      OLEDBSimpleProvider_getRWStatus = OSPRW_READONLY
   Else
      ' Make the column read-write
      OLEDBSimpleProvider_getRWStatus = OSPRW_READWRITE
   End If
End Function

In the Object box, select OLEDBSimpleProvider. In the Procedure box, select the getVariant function. Add the following code to the procedure to return data stored in a specific row and column:
```
Private Function OLEDBSimpleProvider_getVariant _
   (ByVal iRow As Long, ByVal iColumn As Long, _
   ByVal format As OSPFORMAT) As Variant
   OLEDBSimpleProvider_getVariant = MyOSPArray(iRow, iColumn)
End Function
```
The getVariant function also accepts a format argument which can be used to determine the formatting of the data returned.

In the Object box, select OLEDBSimpleProvider. In the Procedure box, select the insertRows function. Add the following code to the procedure to insert a new row of data into a file:

Private Function OLEDBSimpleProvider_insertRows _
   (ByVal iRow As Long, ByVal cRows As Long) As Long
   Dim TempArray()
   Dim listener As OLEDBSimpleProviderListener
   Dim v As Variant

   ' Establish a temporary array
   cNewRows = RowCount + cRows
   ReDim TempArray(cNewRows + 1, ColCount + 1)

   ' If inserting past the end of the array, insert at
   ' the end of the array
   If iRow > RowCount Then
      iRow = RowCount + 1
   End If

   ' Notify listener
   For Each v In colListeners
      Set listener = v
      listener.aboutToInsertRows iRow, cRows
   Next

   ' Copy over the existing rows
   For Row = 0 To iRow
      For Col = 0 To ColCount
         TempArray(Row, Col) = MyOSPArray(Row, Col)
      Next Col
   Next Row

   ' Copy the last rows which follow the inserted rows
   For Row = iRow + 1 + cRows To cNewRows
      For Col = 0 To ColCount
         TempArray(Row, Col) = MyOSPArray(Row - cRows, Col)
      Next Col
   Next Row

   ' Re-allocate the array to copy into it
   ReDim MyOSPArray(cNewRows + 1, ColCount + 1)

   ' Copy over the rows
   For Row = 0 To cNewRows
      For Col = 0 To ColCount
         MyOSPArray(Row, Col) = TempArray(Row, Col)
      Next Col
   Next Row

   ' Clear the temporary array
   ReDim TempArray(0)

   ' Set the real row count back in
   RowCount = cNewRows

   ' Notify listeners
   For Each v In colListeners
      Set listener = v
      listener.insertedRows iRow, cRows
   Next

   ' Return number of inserted rows
   OLEDBSimpleProvider_insertRows = cRows
End Function

In the Object box, select OLEDBSimpleProvider. In the Procedure box, select the isAsynch function. Add the following code to the procedure to determine if the OSP can return data asynchronously:
```
Private Function OLEDBSimpleProvider_isAsync() As Long
   OLEDBSimpleProvider_isAsync = False
End Function
```

In the Object box, select OLEDBSimpleProvider. In the Procedure box, select the removeOLEDBSimpleProviderListener function. Add the following code to the procedure to remove a listener:

Private Sub OLEDBSimpleProvider_removeOLEDBSimpleProviderListener _
   (ByVal pospIListener As OLEDBSimpleProviderListener)
   ' Remove the listener
   For i = 1 To colListeners.Count
      If colListeners(i) Is pospIListener Then
         colListeners.Remove i
      End If
   Next
End Sub

In the Object box, select OLEDBSimpleProvider. In the Procedure box, select the setVariant function. Add the following code to the procedure to retrieve data from a particular row and column and to designate a listener to provide notification that data has changed:

Private Sub OLEDBSimpleProvider_setVariant(ByVal iRow As Long, _
   ByVal iColumn As Long, ByVal format As OSPFORMAT, _
   ByVal Var As Variant)
   Dim listener As OLEDBSimpleProviderListener
   Dim v As Variant

   For Each v In colListeners
      Set listener = v
      listener.aboutToChangeCell iRow, iColumn   ' Pre-notification
   Next

   MyOSPArray(iRow, iColumn) = Var

   For Each v In colListeners
      Set listener = v
      listener.cellChanged iRow, iColumn         ' Post-notification
   Next
End Sub

In the Object box, select OLEDBSimpleProvider. In the Procedure box, select the stopTransfer function. Add the following code to the procedure:
```
Private Sub OLEDBSimpleProvider_stopTransfer()
   ' Do nothing because we are already populated
End Sub
```
Note that there is no code in this procedure, but the procedure must be included because this class implements OLEDBSimpleProvider. You could add code here that would allow you to cancel loading during a long transfer.
Choose Save Project Group from the File menu to save your changes. When prompted for a file name for the Class module, choose the default (MyOSPObject.cls). When prompted for a file name for the Project, choose the default (MyDataComponent.vbp).

Whew! If that seemed like a lot of code, there's a good reason for it — the MyOSPObject class provides much of the functionality that you might find in a database. With OSP, you can use almost any file as you might have used a database in the past.

In the next step, we'll create another class that acts as the data source to the MyOSPObject class.

Step by Step

This topic is part of a series that walks you through creating sample ActiveX data sources.

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Go to the next step	Creating the MyDataSource Class
Start from the beginning	Creating Data Sources

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