Arraylist sort and binarysearch

[T120]

Guys - I have a windows app and I'm trying to cache images in memory. I have:-

Public TileCache As New ArrayList

    Structure TileCacheDescriptor

        Public TileURL As String
        Public TileLayer As String
        Public TileImage As Image

    End Structure

   Dim TileDetails As New TileCacheDescriptor
   TileDetails.TileImage = ThisMap.TileGrid(C - Col + w, T - CentreTile + w).TileImage
   TileDetails.TileURL = src
   TileDetails.TileLayer = Layer
   TileCache.Add(TileDetails)
   TileCache.Sort()
                   

I think I have to sort the array to be able to use binarysearch.
So I need to sort the arraylist on TileDetails.TileURL(if possible) and then binarysearch on it.

Any hints much appreciated