How to update a property of a Private List(Of T) in nested loops?

Question

Some background:
I have an HTML file with page dimensions contained in DIV tags and data contained in SPAN tags. The SPAN tags are children of DIV tags. SPAN tags are positioned by setting each one's "left" and "top" in the style attribute. There are several SPAN tags per row but only determined by their "top" and "left". The SPAN tags are ordered in an arbitrary way within a DIV tag.

I've managed to load all the tag properties into a List(Of Node) and sort them the way I need. How do I update the "Order" property of the _allData list?

Public Structure Node
    Public Underline As Boolean ' text-decoration: underline
    Public InnerText As String ' content/data
    Public Order As Integer ' initially all 0
    Public Top As Single ' relative position of tag to TopOffset
    Public Left As Single ' relative position of tag to TopOffset
    Public TopOffset As Single ' page's postion from 0,0
End Structure

Private _allData As List(Of Node)

Private Sub SetGlobalElementsOrder()
    Dim currentOrder As Integer = 0

    ' not really points of anything but 
    ' a useful built-in structure to store 2 values of type Single
    Dim pageColumns As IEnumerable(Of PointF) = {
        New PointF(0, 2.2), 
        New PointF(2.45, 4.1),
        New PointF(5.1, 7.35)}

    ' this has values like: 10.29, 20.55, 30.92, ...
    Dim topOffsets As IEnumerable(Of Single) =
        _allData.Select(Function(its) its.TopOffset).Distinct.ToList

    ' sort each page separately
    For Each topOffset As Single In topOffsets

        ' select each column's tags whose "left" is between X and Y of PointF
        For Each columnLimit As PointF In pageColumns

            Dim columnTags As List(Of Node) = CType((From node In _allData
                                                               Where node.TopOffset = topOffset AndAlso node.Left > columnLimit.X AndAlso node.Left < columnLimit.Y
                                                               Order By node.Top, node.Left), 
                                                            List(Of Node))

            For Each tag As Node In columnTags

                ' keep updating this value for all processed tags
                currentOrder += 1

                ' <@:o(
                ' _allData.Find(Function(its) its.Equals(tag)).Order = currentOrder
                ' _allData(_allData.IndexOf(tag)).Order = currentOrder
            Next
        Next
    Next
End Sub

Redeclare your `Structure` as `Class`. That way you avoid copying and therefore can assing `.Order` right on the instance you have in `columnTags`. — GSerg, Jul 08 '14 at 22:44
@NicoSchertler Not only that - you wouldn't be able to [assign to a struct's member stored in a list](http://stackoverflow.com/a/441323/11683) anyway. — GSerg, Jul 08 '14 at 22:52
Redeclaring the Node structure as Class solved the problem. Thanks! This works for me: _allData(_allData.IndexOf(tag)).Order = currentOrder — Ruutsa, Jul 08 '14 at 23:43

How to update a property of a Private List(Of T) in nested loops?

0 Answers0