Sort on two columns in ListView?

  • Thread starter Thread starter vb newbie
  • Start date Start date
V

vb newbie

Does anybody have suggestions on how to programatically sort a ListView
on TWO subitem columns?
Here's the code I'm using to sort on one subitem:

Public Function Compare(ByVal x As Object, ByVal y As _
Object) As Integer Implements _
System.Collections.IComparer.Compare
Dim item_x As ListViewItem = DirectCast(x, _
ListViewItem)
Dim item_y As ListViewItem = DirectCast(y, _
ListViewItem)

' Get the sub-item values.
Dim string_x As String
If item_x.SubItems.Count <= m_ColumnNumber Then
string_x = ""
Else
string_x = item_x.SubItems(m_ColumnNumber).Text
End If

Dim string_y As String
If item_y.SubItems.Count <= m_ColumnNumber Then
string_y = ""
Else
string_y = item_y.SubItems(m_ColumnNumber).Text
End If

' Compare them based on column types
Select Case (Form1.sortTypes(m_ColumnNumber))
Case "c"
If m_SortOrder = SortOrder.Ascending Then
Return String.Compare(string_x, string_y)
Else
Return String.Compare(string_y, string_x)
End If
Case "d"
If m_SortOrder = SortOrder.Ascending Then
Return Date.Compare(string_x, string_y)
Else
Return Date.Compare(string_y, string_x)
End If
Case "n"
If m_SortOrder = SortOrder.Ascending Then
Return Decimal.Compare(string_x, string_y)
Else
Return Decimal.Compare(string_y, string_x)
End If

End Select
End Function
 
Yep.

I didn't test in VB itself, but I'm pretty sure this transformation of
your code does what you want.

Assume m_ColumnNumber is now an array (to hold multiple column
numbers). And there's another variable, NumOfSortColumns, to tell the
Compare routine how many columns it's working with.

Public Function Compare(ByVal x As Object, ByVal y As _
Object) As Integer Implements _
System.Collections.IComparer.Compare
Dim item_x As ListViewItem = DirectCast(x, _
ListViewItem)
Dim item_y As ListViewItem = DirectCast(y, _
ListViewItem)
Dim string_x, string_y As String
Dim SortColumn As Integer
Dim ColumnNumber As Integer
Dim Result As Integer

For SortColumn = 0 to NumOfSortColumns-1
ColumnNumber = m_ColumnNumber(SortColumn)

' Get the sub-item values.
If item_x.SubItems.Count <= ColumnNumber Then
string_x = ""
Else
string_x = item_x.SubItems(ColumnNumber).Text
End If
If item_y.SubItems.Count <= ColumnNumber Then
string_y = ""
Else
string_y = item_y.SubItems(ColumnNumber).Text
End If

' Compare them based on column types.
Select Case (Form1.sortTypes(ColumnNumber))
Case "c": Result = String.Compare(string_x, string_y)
Case "d": Result = Date.Compare(string_x, string_y)
Case "n": Result = Decimal.Compare(string_x, string_y)
End Select

' Reverse the sign on the sort result if sorting descending.
If m_SortOrder = SortOrder.Descending Then Result *= -1

' Set the return value to the result.
' If result is non-zero (not equal), exit immediately.
' But if result is zero (equal), compare the next sort column
(if available).
Compare = Result
If Result <> 0 Then Exit Function

Next

End Function
 
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