VB.NET Filtering ListItems Problem

Question

I am trying to filter a ListBox based on the presence of a string. Basically, if there is a ListItem that doesn\'t contain the string then I want to remove all ListItems that do

Answer 1

When removing items from a list there are a couple of options. As you've discovered, modifying the collection in a foreach loop isn't going to work. A for loop that counts down is the answer as @balpha mentioned.

Another option is to store a list of items in a separate list, then iterate over that to remove items from the original list. Yet another option is to use LINQ.

Sample list:

Dim stringList As New List(Of String)
stringList.Add("W:foo")
stringList.Add("bar")
stringList.Add("barW:")
stringList.Add("foo")

Reverse For Loop

For i As Integer = stringList.Count - 1 To 0 Step -1
    If stringList(i).IndexOf("W:") > -1 Then stringList.RemoveAt(i)
Next

ForEach with 2 Lists

Dim removeList As New List(Of String)
' store items to remove here
For Each s As String In stringList
    If s.IndexOf("W:") > -1 Then removeList.Add(s)
Next
' remove stored items here
For Each s As String In removeList
    stringList.Remove(s)
Next

LINQ

In this snippet I filter on IndexOf = -1 instead of > -1 to keep what I want rather than filter what I don't want.

stringList = stringList.Where(Function(s) s.IndexOf("W:") = -1).ToList()