Question

I am trying to sort a DataGridView control by a column that contains DBNull values. This DataGridView control is bound to an SQL Server 2012 Database.

When I click the headercell (to sort in ascending order), the DBNull values are sorted ahead of the rest of the integer values, so that the top rows in the column are all blank, and then after that the integer values 1,2,3 etc are in ascending order.

How do I get around this? I would rather the DataGridView control sort the rows with values at the top, followed by the DBNulls.

I have tried to insert a higher value into the blank cells, which then sorts them correctly, but when I return those values back to System.DBNull.value, the sort order reverts back to the way above.

My code is as follows:

If dgv.Columns(e.ColumnIndex).Name.EndsWith("Position") Then
    intSortingRunningPosition = 1000
    dgv.Sort(baseColumn, System.ComponentModel.ListSortDirection.Ascending)
    newColumn.HeaderCell.SortGlyphDirection = Windows.Forms.SortOrder.Ascending
    For Each dr As DataGridViewRow In dgv.Rows
        If dr.Cells(e.ColumnIndex).Value Is System.DBNull.Value Then 
            dr.Cells(e.ColumnIndex).Value = intSortingRunningPosition
            intSortingRunningPosition += 1
        End If
    Next
    dgv.Sort(newColumn, System.ComponentModel.ListSortDirection.Ascending)
    For Each dr As DataGridViewRow In dgv.Rows
        If dr.Cells(e.ColumnIndex).Value >= 1000 Then
            dr.Cells(e.ColumnIndex).Value = System.DBNull.Value
        End If
    Next
End If

Sorry if this is confusing. Thanks!

Update:

I have modified my code to work with the IComparer method, and have come up with the following:

 Public Function Compare(ByVal x As Object, ByVal y As Object) As Integer _
     Implements System.Collections.IComparer.Compare

     Dim DataGridViewRow1 As DataGridViewRow = CType(x, DataGridViewRow)
     Dim DataGridViewRow2 As DataGridViewRow = CType(y, DataGridViewRow)
     Dim CompareResult As Integer
     Dim intDGV1Cell0Value As Integer = Nothing
     Dim intDGV1Cell1Value As Integer = Nothing
     Dim intDGV2Cell0Value As Integer = Nothing
     Dim intDGV2Cell1Value As Integer = Nothing

     Try
         intDGV1Cell0Value = CInt(DataGridViewRow1.Cells(0).Value)
     Catch ex As Exception
         intDGV1Cell0Value = Int32.MaxValue
     End Try
     Try
         intDGV1Cell1Value = CInt(DataGridViewRow1.Cells(1).Value)
     Catch ex As Exception
         intDGV1Cell1Value = Int32.MaxValue
     End Try
     Try
         intDGV2Cell0Value = CInt(DataGridViewRow2.Cells(0).Value)
     Catch ex As Exception
         intDGV2Cell0Value = Int32.MaxValue
     End Try
     Try
         intDGV2Cell1Value = CInt(DataGridViewRow2.Cells(1).Value)
     Catch ex As Exception
         intDGV2Cell1Value = Int32.MaxValue
     End Try

     ' Try to sort based on the Last Name column.
     CompareResult = System.String.Compare(intDGV1Cell1Value, intDGV2Cell1Value)

     ' If the Last Names are equal, sort based on the First Name. 
         If CompareResult = 0 Then
             CompareResult = System.String.Compare(intDGV1Cell0Value, intDGV2Cell0Value)
         End If

     Return CompareResult * sortOrderModifier
 End Function

The null value is now not sorting at all. Any ideas on what I am doing wrong here? I am sure I am a bit out of the ballpark as it is…

Answer 1

I was fairly unsucessful using the Sort(ICompare) method to sort this database because it was bound to an external dataset. I ended up modifying my connection string and refilling the datatable.

My code is as follows:

If DataType = "Integer" Then
    If Column = "Vehicle Number" Then
        strConnectionStringCase = "Select * From Timing ORDER BY CAST([Class] AS NVARCHAR(MAX)) " & Direction & ", CONVERT(int, RTRIM(CAST([" & Column & "] AS NVARCHAR(MAX)))) " & Direction
    End If        
ElseIf DataType = "DateTime" Then
    strConnectionStringCase = "Select * From Timing ORDER BY CASE WHEN [" & Column & "] is NULL THEN 1 ELSE 0 END, [" & Column & "] " & Direction
ElseIf DataType = "String" Then
    If Column = "Vehicle Number" Then
        strConnectionStringCase = "Select * From Timing ORDER BY LEN(CAST([" & Column & "] AS NVARCHAR(MAX))) " & Direction & ", CAST([Class] AS NVARCHAR(MAX)) " & Direction & ", CAST([" & Column & "] AS NVARCHAR(MAX)) " & Direction
    End If
End If

I call this subroutine on the header cell click event. I send the Column name, sort direction, and datatype to this subroutine.

This code also allows me to sort the column depending on the type of data. If there are alphanumeric strings, I can sort them in a similar order as if they were only integers. The DBNull values are always placed at the end of the sort.

Thanks for the help!