Situation:
I have a grid with columns "NAME" and "DATE". When sorting (ascending) on date, all rows without a date should be placed at the end of the rowcollection (like when sorting descending).
This is what i'm currently doing:
Private Sub gridcandidates_AfterSortChange(ByVal sender As System.Object, ByVal e As Infragistics.Win.UltraWinGrid.BandEventArgs) Handles gridcandidates.AfterSortChange
Dim col As UltraGridColumn = e.Band.Columns("DATE") If col.SortIndicator = SortIndicator.Ascending Then For i As Integer = gridcandidates.Rows.Count - 1 To 0 Step -1 If Not IsDBNull(gridcandidates.Rows(i).Cells("DATE").Value) Then gridcandidates.Rows.Move(gridcandidates.Rows(i), 0) 'Move row to beginning Else gridcandidates.Rows.Move(gridcandidates.Rows(i), gridcandidates.Rows.Count - 1) 'Move row to end End If Next End If
End Sub
Question/problems:
- It messes up the sort... the columns aren't sorted by date.
- Is there anyway to improve the code? I'm sure i'm overlooking something!
Hi Martin,
Yeah, it was a good tip. I wasn't contradicting you, just wanted to explain in more detail why that line of code was there so everyone understands the ramifications of changing it.
I, too, find it surprising that the GroupBy functionality uses the SortComparer on the column to determine equality when grouping.
I understand what it is for, I just wanted to point out that it breaks the group by. I wasn't expecting that, so I thought it was worth pointing out.
The code you are referring to is there so that the sorting is never arbitrary. Without that peice of code, what happens is that when you have a group of rows with the same value, they will be sorted in essentially random order. This means if you sort the same column twice, the rows with values that are the same will come out in a different order each time.
A better solution to the GroupBy problem might be to use a customer GroupByEvaluator, rather than relying on the SortComparer to determine equality of columns. But quite frankly, I'm surprised the grid looks at the SortComparer for grouping, anyway.
Just a note on the following section of code:
// If the two values are the same, compare the row index. // This isn't really neccessary, but it makes the sorting more reliable. // We won't get random switching of like values when sorting multiple // times. if (xObject.Equals(yObject)) return xCell.Row.Index.CompareTo(yCell.Row.Index);
If you use this then the Group By function does not work correctly. It will think each item is different and won't group together the same items. If this is a problem for you then replace that section of code with:
if (xObject.Equals(yObject)) return 0;
This indicates that the objects are the same and the Group By function will work again.
Works great, thanks! I just had to switch around the return values in the line "return ascending ? 1 : -1;" to make it work for me. I had guessed it had something to do with the switching/sorting. Thanks again!