How to sort items in a collection?

Posted on 2003-03-18
Medium Priority
Last Modified: 2012-06-27
There are two classes: DocCatalog and DocCatalogList.
How can I sort the DocCatalog items in a DocCatalogList by

    Public Class DocCatalog
        Public Function Rating() As Integer
        End Function
    End Class
   Public Class DocCatalogList
        Inherits CollectionBase

        Sub New()

        End Sub

        'Add a DocCataLog in this list
        Sub Add(ByVal catalog As DocCatalog)
            ' list is inherts from CollectionBase
        End Sub

    End Class
Question by:tyknight
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LVL 28

Accepted Solution

iboutchkine earned 150 total points
ID: 8166284
You can convert collection to array

' Converts a StringCollection to an array of strings.
Public Function StringCollectionToArray(ByRef col As System.Collections.Specialized.StringCollection) As String()

    ' Instantiate an array and sets the array to be equal to the StringCollection's size.
    Dim aOut(col.Count()) As String

    ' Copy the contents of the collection to the array, beginning at the first element of the array.
    col.CopyTo(aOut, 0)

    ' Return the array to the caller.
    Return aOut

End Function

Sort array and then convert it back to collection

' Converts an array of strings to a StringCollection.
Public Function ArrayToStringCollection(ByRef aIn() As String) _
     As System.Collections.Specialized.StringCollection

    ' Instantiate new StringCollection object.
    Dim sc As System.Collections.Specialized.StringCollection =  _
         New System.Collections.Specialized.StringCollection()

    ' Populate the StringCollection with the specified array.

    ' Return the new StringCollection to the caller.
    Return sc

End Function

Let me know if you need the code how to sort array

Author Comment

ID: 8171564

I found the following function and modified the code to sort my collection.

Public Function SortItemCollection(col As Collection, strPropertyName, Optional blnCompareNumeric As Boolean = False) As Collection
    Dim colNew As Collection
    Dim objCurrent As Object
    Dim objCompare As Object
    Dim lngCompareIndex As Long
    Dim strCurrent As String
    Dim strCompare As String
    Dim blnGreaterValueFound As Boolean

    'make a copy of the collection, ripping through it one item
    'at a time, adding to new collection in right order...
    Set colNew = New Collection
    For Each objCurrent In col
        'get value of current item...
        strCurrent = CallByName(objCurrent, strPropertyName, VbGet)
        'setup for compare loop
        blnGreaterValueFound = False
        lngCompareIndex = 0
        For Each objCompare In colNew
            lngCompareIndex = lngCompareIndex + 1
            strCompare = CallByName(objCompare, strPropertyName, VbGet)
            'optimization - instead of doing this for every iteration, have 2 different loops...
            If blnCompareNumeric = True Then
                'this means we are looking for a numeric sort order...
                If Val(strCurrent) < Val(strCompare) Then
                    'found an item in compare collection that is greater...
                    'add it to the new collection...
                    blnGreaterValueFound = True
                    colNew.Add objCurrent, , lngCompareIndex
                    Exit For
                End If
                'this means we are looking for a string sort...
                If strCurrent < strCompare Then
                    'found an item in compare collection that is greater...
                    'add it to the new collection...
                    blnGreaterValueFound = True
                    colNew.Add objCurrent, , lngCompareIndex
                    Exit For
                End If
            End If
        'if we didn't find something bigger, just add it to the end of the new collection...
        If blnGreaterValueFound = False Then
            colNew.Add objCurrent
        End If

    'return the new collection...
    Set SortItemCollection = colNew
    Set colNew = Nothing

End Function

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