Expandable Grid

I use this function for expanding and contracting hidden rows in my grid, is there anyway I can use this function to setup an expand all button

Code:

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Private Sub Dg_ItemCommand(ByVal source As System.Object, ByVal e As System.Web.UI.WebControls.DataGridCommandEventArgs) Handles dg.ItemCommand
        Select Case e.CommandName
            Case "Expand"
                Dim ExpandedContent As PlaceHolder = e.Item.Cells(dg.Columns.Count - 1).FindControl("ExpandedContent")
                ExpandedContent.Visible = Not ExpandedContent.Visible


                Dim btnExpand As ImageButton = e.Item.Cells(0).FindControl("btnExpand")
                If btnExpand.ImageUrl = "~/Images/Plus.gif" Then
                    btnExpand.ImageUrl = "~/Images/Minus.gif"
                Else
                    btnExpand.ImageUrl = "~/Images/Plus.gif"
                End If
        End Select

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