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Tip of the Day
Language: VB7
Expertise: Intermediate
Sep 8, 2003

Skipping columns when tabbing on a DataGrid

It happens quite often that you have a DataGrid with hidden columns (with width = 0), because you need their values but don't want to show them to the user. However, when you tab through the DataGrid's columns, these "hidden" columns are still taken into account in the tab order. This means that when the user presses the Tab key the focus might seem to disappear from the DataGrid and the form, when in reality it is on the hidden cell. This behavior is not very user friendly, and may leave the user wondering what happened, and if he has to click somewhere or press Tab again. It would be much better if the Tab could skip some columns, so that everything work as if those hidden columns were not there at all. This skipping mechanism could also be useful in other situations, when you have visible columns but don't want the user to be able to give them the focus, either by pressing Tab or by clicking directly on them. You can solve this problem by handling the DataGrid's CurrentCellChanged event, and simulate a Tab keypress when the user selects an "inaccessible" column. Here's the code to enable/disable the column-skipping mechanism:

' Enable the column-skipping mechanism for the input grid,
'  and for the columns with the specified index
' Example: skip the 2nd (index 1) and 4th (index 3) columns
'   EnableDataGridColumnSkip(DataGrid1, 1, 3)

Sub EnableDataGridColumnSkip(ByVal grid As DataGrid, _
    ByVal ParamArray columnsToSkip() As Integer)
    ' save the array of column indexes in the grid's Tag property
    grid.Tag = columnsToSkip
    ' attach the grid's CurrentCellChanged event to the 
    ' GenDataGrid_CurrentCellChanged event handler
    AddHandler grid.CurrentCellChanged, AddressOf GenDataGrid_CurrentCellChanged
End Sub

' Disable the column-skipping mechanism for the input grid
' Example: DisableDataGridColumnSkip(DataGrid1)

Sub DisableDataGridColumnSkip(ByVal grid As DataGrid)
    ' detach the grid's CurrentCellChanged event from the 
    ' GenDataGrid_CurrentCellChanged event handler
    RemoveHandler grid.CurrentCellChanged, _
        AddressOf GenDataGrid_CurrentCellChanged
End Sub

' Handle the grid's CurrentCellChanged, to skip the columns whose index is 
' found in the array stored in grid's Tag property

Sub GenDataGrid_CurrentCellChanged(ByVal sender As Object, _
    ByVal e As System.EventArgs)
    ' cast the generic sender Object to a DataGrid
    Dim grid As DataGrid = DirectCast(sender, DataGrid)
    ' cast the grid's Tag to an array of Integers, that contains the indexes of 
    ' the columns to skip
    Dim columnsToSkip() As Integer = DirectCast(grid.Tag, Integer())
    ' get the index of the current column
    Dim currColIndex As Integer = grid.CurrentCell.ColumnNumber
    ' if the current column's index is found in the columnsToSkip array,
    '  simulate a TAB key press,
    ' so that the focus is moved to the next column in the same row,
    '  or to the next row if this is the last column
    If Array.IndexOf(columnsToSkip, currColIndex) > -1 Then
        SendKeys.Send("{TAB}")
    End If
End Sub
Marco Bellinaso
 
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