PRB: Grid Custom Control: LeftCol/TopRow Valid Values (80911)

MORE INFORMATION

A program can determine the maximum values allowed for LeftCol and TopRow by setting these properties to each valid column and row number, respectively, and then determining if the assignment caused an error. The example code below shows how to use this method.

The minimum values allowed for LeftCol and TopRow are always given by the values of the Grid custom control properties FixedCols and FixedRows, respectively.

Step-by-Step Example

1. 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.
2. From the File menu, choose Add File, and select the GRID.VBX custom control file. The Grid tool will appear in the Toolbox.
3. Select the Grid tool from the Toolbox, and add a grid (Grid1) to Form1.
4. Size the Grid and choose values for the Cols and Rows properties of the Grid.
5. Place a command button (Command1) on Form1.
6. Enter the following code in the Command1_Click event procedure:

      ' Example of how to call Grid_Scroll_Range to determine the
      ' range of values for Grid properties LeftCol and TopRow.
      Sub Command1_Click ()
         Dim msg As String          ' message string
         Dim max_LeftCol As Single  ' maximum LeftCol
         Dim max_TopRow As Single   ' maximum TopRow
   
         Call grid_scroll_range(grid1, max_LeftCol, max_TopRow)
   
         msg = "Valid Grid.LeftCol: "
         msg = msg + Format$(grid1.FixedCols) + ".."
         msg = msg + Format$(max_LeftCol) + Chr$(13) + Chr$(10)
         msg = msg + "Valid Grid.TopRow: "
         msg = msg + Format$(grid1.FixedRows) + ".."
         msg = msg + Format$(max_TopRow)
   
         MsgBox msg
      End Sub
   						

7. Enter the following code in the general Declarations section:

      ' grid_scroll_range
      '   Determines the maximum values allowable for grid LeftCol
      '   and TopRow. Minimum values are FixedCols and FixedRows.
      '   Parameters:
      '       grid    -- a Grid control
      '       LftMax  -- return value, maximum LeftCol value
      '       TopMax  -- return value, maximum TopRow value
      '
      Sub grid_scroll_range (grid As Control, LftMax!, TopMax!)
         Dim save As Integer     ' for restoring grid properties
   
         ' Calculate LftMax
         ' Try each column number to see if it causes a run-time
         ' error. Go in reverse order to minimize the number of
         ' tries to the number of columns displayed in the grid.
         save = grid.LeftCol
         On Error Resume Next
         For LftMax = grid.Cols - 1 To grid.FixedCols + 1 Step -1
            Err = 0
            grid.LeftCol = LftMax
            If Err = 0 Then
               Exit For
            End If
         Next
         grid.LeftCol = save
   
         ' Calculate TopMax
         ' Try each row number to see if it causes a run-time
         ' error. Go in reverse order to minimize the number of
         ' tries to the number of rows displayed in the grid.
         save = grid.TopRow
         On Error Resume Next
         For TopMax = grid.Rows - 1 To grid.FixedRows + 1 Step -1
            Err = 0
            grid.TopRow = TopMax
            If Err = 0 Then
               Exit For
            End If
         Next
         grid.TopRow = save
      End Sub