VB：向后循环通过列表

Question

I have set up a For Each statement that loops through a list. The list is made up of 'pixels' which is a custom picturebox class. I need to setup a loop that goes through the list in reverse order. This is what my normal loop looks like:

        For Each Tile As Pixel In PixelList
            If Tile.PixelNumber = 1 Then
                Tile.NewColour()
            End If
        Next

PixelNumber is just a integer variable that keeps count of which pixel is which.

Pixel is the custom Picturebox class

PixelList is the name of the list

I need to be able to setup a similar loop but one that goes through the list in reverse order of when I Tile was added. So a first in first out situation.

Answer 1

вʀaᴎᴅᴏƞ вєнᴎєƞ's way is the most efficient, but a simple alternative would be to use the List(Of T).Reverse() function , though that changes the order of the list itself.

    PixelList.Reverse()
    For Each Tile As Pixel In PixelList
        If Tile.PixelNumber = 1 Then
            Tile.NewColour()
        End If
    Next

Answer 2

Access the list by an index that starts at the count of elements in the collection and decrements by one.

For i as Integer = PixelList.Count - 1 To 0 Step -1
    If DirectCast(PixelList(i), Pixel).PixelNumber = 1 then DirectCast(PixelList(i), Pixel).NewColour()
Next