Hi Maya,

Thanks for the reply.

The columns are cleared only in response to the user clicking on a non-grid control (usually a menu item).  I believe this always generates a full postback (not AJAX).

The grid is actually in a User Control so the page life-cycle looks something like this:

First Load:

1. Control_Init
   Does nothing to the grid (declarative Checkbox Column already exists)
2. Page_Load
   Sets ShowCheckbox variable to indicate the Checkbox column is needed
   Adds several columns via code
   Sets DataSource to a DataView object (AutoGenerateColumns is set to false)
3. Sets DataLoaded variable indicating grid is loaded 
4. Control_Load
   Does nothing to the grid but adds CSS and Script references to the page
5. Page OnPreRender
   Does nothing since DataLoaded is already true
6. Control OnPreRender
   Sets grid selection behavior to Cell mode

Page renders correctly
User elects to change grid content

Page Postback (non-ajax):

1. Control_Init
   Does nothing to the grid
   (Confirmed Checkbox Column still exists)
2. Page_Load
   Does nothing to the grid 
3. Control_Load
   Does nothing to the grid but adds CSS and Script references to the page
4. Control_Click event that changes the Datasource
   Calls ClearDataSource
   Calls Columns.Clear
   Manually re-creates TemplatesDataField column with WebDataGridCheckbox control since it is now cleared
   Calls SortedColumns.Clear
   Calls Filtering.ClearBehaviorColumnInfo 
   Adds several columns via code
   Sets DataSource to a DataView object (AutoGenerateColumns is set to false)
5. Page OnPreRender
   Does nothing since DataLoaded is already true
6. Control OnPreRender
   Sets grid selection behavior to Cell mode

Page renders correctly
User elects to page the grid

Ajax Page Postback:

1. Control_Init
   Does nothing to the grid
   (Confirmed Checkbox Column still exists)
2. Page_Load
   Does nothing to the grid 
3. Control_Load
   Does nothing to the grid but adds CSS and Script references to the page
4. Page OnPreRender
   Since DataLoaded is false
   Adds several columns via code
   Sets DataSource to a DataView object (AutoGenerateColumns is set to false)
5. Control OnPreRender
   Sets grid selection behavior to Cell mode

Page renders without the Checkbox column, but no Checkboxes visible.

Having traced through the code now to confirm the above, I think the problem lies with the need to manually recreate the Declaritive column after calling Columns.Clear().

I think the code that generates this column is not working.  It looks like this:

Dim chkSel = Grid.Columns.FromKey("chkSel")
If chkSel Is Nothing Then
   Dim chk As New WebDataGridCheckbox("chkSel")
   Dim tdf As New TemplateDataField(False)
   tdf.ItemTemplate = chk
   tdf.Key = chk.Key
   tdf.Width = New Unit(30)
   tdf.Hidden = Not ShowCheckbox
   Grid.Columns.Add(tdf)
End If

And the WebDataGridCheckbox class, looks like this:

Public Class WebDataGridCheckbox
   Implements ITemplate
   Private _Key As String
   Public ReadOnly Property Key As String
      Get
         Return _Key
      End Get
   End Property
   Private _DataFieldName As String
   Public ReadOnly Property DataFieldName As String
      Get
         Return _DataFieldName
      End Get
   End Property
   Public Sub New(Key As String)
      _Key = Key
      _DataFieldName = Key
   End Sub
   Public Sub InstantiateIn(container As System.Web.UI.Control) Implements ITemplate.InstantiateIn
      Dim chk = New CheckBox()
      chk.ID = Key
      container.Controls.Add(chk)
   End Sub
End Class

I think I got this code from one of the posts on this forum.

I would really appreciate any help converting this Declarative column definition to Code:

<ig:TemplateDataField Header-Text="" Key="chkSel" Width="30">
  <ItemTemplate>
     <input type="checkbox" id="chkSel" runat="server" />
  </ItemTemplate>
</ig:TemplateDataField>

Regards,
pp James Kydd