[RESOLVED] [2005] problem with for each loop through listbox items

Hi

I am trying to execute this code as part of a backgroundworker thread:

Code:

---

        For Each stockedItem As String In lstStock.Items
            For Each toBuyItem As String In lstBuy.Items
 
                If stockedItem.ToLower = toBuyItem.ToLower Then
                'my code here
                End If
 
 
            Next
        Next

---

But it is throwing an exception (on the bold/underlined line) saying that "The list this enumerator has been bound to has been modified"..

can anyone help me solve this problem because i'm not sure what to do..

thanks :)

Since you want to remove something from one of your ListBoxes you need to loop backward through them in order to avoid that error.

vb.net Code:

For i As Integer = Me.ListBox1.Items.Count - 1 To 0 Step -1
    If somecondition Then
        Me.ListBox1.Items.RemoveAt(i)
    End If
Next i

You may also find the ListBox.Items.Contains property easier to work with if you are checking against another collection. :thumb:

You've left out the most important part!
Post the "my code here" part.

Quote:

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Originally Posted by nmadd

Since you want to remove something from one of your ListBoxes you need to loop backward through them in order to avoid that error.

---

huh? :s i'm not trying to remove anything from either listbox..
i am trying to loop through both listboxes, compare each item against each item from the other listbox, and then if it finds an item which is in BOTH listboxes, then it should execute my code..


penagate.. here is my full code :

Code:

---

        For Each stockedItem As String In lstStock.Items
            For Each toBuyItem As String In lstBuy.Items

                If stockedItem.ToLower = toBuyItem.ToLower Then
                    worker.ReportProgress(35, "Found an item match!")
                    Dim rRegEx2 As Regex
                    Dim mMatch2 As Match

                    rRegEx2 = New Regex(myregexhere)

                    mMatch2 = rRegEx2.Match(HTML)

                    If mMatch2.Success Then
                        worker.ReportProgress(40, "Gathering Information")

                        Timer.Enabled = False

                        Try
                            Dim number As Integer = lstStock.Items.IndexOf(stockedItem)
                            lstStock.SetSelected(number, True)
                            Dim number2 As Integer = lstBuy.Items.IndexOf(stockedItem)
                            lstBuy.SetSelected(number2, True)
                        Catch
'if it throws an exception, it just means the letter-case of stockedItem does not match the letter-case of the item in the listbox.. but this won't happen much and it doesn't really matter if it doesn't get selected!
                        End Try


                        Dim cost As String = mMatch2.Groups(3).ToString

                        Dim smartCost As Integer = myModule.SMARTCost(cost)

                        continueRefresh = False

                        ItemCost = smartCost
                        ItemName = stockedItem
                    Else
                        'a strange error occured if we end up here :s
                        MsgBox("Debug: Error with regex match")
                    End If
                Else
                    'no matches
                End If

            Next
        Next

---

and thanks for helping :)

I can only think of one thing.

Comment out the following line of the Try block:

VB.NET Code:

lstBuy.SetSelected(number2, True)

—and see if it runs.

ah :D that worked :)
thanks for helping!

oh actually i've got another small problem relating to the same thing so maybe you could help me fix that too? ;)


I wrote this function which is meant to remove duplicate items in a listbox.. so if there is an item there more than once it should delete the others so there's only one of them..

but it throws the same exception as my other problem :|

Code:

---

    Public Function removeDupes(ByVal listbox As Windows.Forms.ListBox)
        Dim removedcount As Integer = 0
        For Each item As String In listbox.Items
            For Each item_compare As String In listbox.Items
                If item = item_compare Then
                    listbox.Items.Remove(item_compare)
                    removedcount += 1
                End If
            Next
        Next
        Return removedcount
    End Function

---

any idea what i can do to fix this one? :p

Edit: also, is there a way to make it so that it ignores case? so it will remove duplicates including when the case is differerent, e.g. anITEM and anItem

Here's a slightly more efficient way:

Code:

---

Public Function removeDupes(ByVal listbox As Windows.Forms.ListBox)
  Dim newItems As New List(Of String)
 
  For Each o As Object In listbox.Items
    Dim s As String = DirectCast(o, String)
   
    If (Not newItems.Contains(s)) _
      newItems.Add(s)
  Next
 
  listbox.Items.Clear()
 
  For Each item As String In newItems: _
    listbox.Items.Add(item)
End Function

---

Case-insensitive is a bit less elegant.

Code:

---

Public Function removeDupes(ByVal listbox As Windows.Forms.ListBox)
  Dim newItems As New List(Of String)
 
  For Each o As Object In listbox.Items
    Dim s As String = DirectCast(o, String)
    Dim exists As Boolean = False
   
    For Each item As String In newItems
      If (String.Compare(s, item, True) = 0) Then
        exists = True
        Exit For
      End If
    Next
   
    If (Not Exists) _
      newItems.Add(s)
  Next
 
  listbox.Items.Clear()
 
  For Each item As String In newItems: _
    listbox.Items.Add(item)
End Function

---

Ok thanks but I'm having a problem with it :|

I think you left out a couple of Next's and an End If and I tried to put them in myself but maybe I did it wrong.. because when I tried it on a list where it should have removed one duplicates, it said it removed 0 and it removed all items from the listbox :S

Here's the code I tried:

Code:

---

    Public Function removeDupes(ByVal listbox As Windows.Forms.ListBox)
        Dim removed As Integer = 0

        Dim newItems As New List(Of String)

        For Each o As Object In listbox.Items

            Dim s As String = DirectCast(o, String)
            Dim exists As Boolean = False

            For Each item As String In newItems
                If (String.Compare(s, item, True) = 0) Then
                    exists = True
                    Exit For
                End If

                If (Not exists) Then
                    newItems.Add(s)
                Else
                    removed += 1
                End If

            Next
        Next

        listbox.Items.Clear()

        For Each item As String In newItems _
        : listbox.Items.Add(item)
        Next

        Return removed

    End Function

---

I do not think I left out any Next's or End If's, although it is possible that I made a mistake. Did you try the code exactly as posted?

To find out how many items were removed, just read the listbox.Items.Count property before and after calling the function.

Quote:

---

Originally Posted by penagate

I do not think I left out any Next's or End If's, although it is possible that I made a mistake. Did you try the code exactly as posted?

To find out how many items were removed, just read the listbox.Items.Count property before and after calling the function.

---

oh,
yes I tried it exactly as you posted it and it was giving me a couple of errors about missing Next and a missing End If so that's why I tried to add them in :|

OK, sorry.
I left out a "Then".

Code:

---

If (Not Exists) Then _

---

oh, thanks a lot :)
it's working very nicely now!