Whats the best way to avoid adding duplicates to a listbox?

[qpabani]

in vb.net?

[nswan]

if you are getting the values from a database using a SQL statement you could do select distinct row and i think that will only bring out individual values.

[qpabani]

its not like that...

[TheExtreme]

Add a Key Value by inherting the ListViewItem in your own class like below. Then iterate through the keys every time you add a listitem to see if it exsists. Don't worry This is very fast due to the IDictionaryEnumerator Interface.

Public Class MyListViewItem
Inherits System.Windows.Forms.ListViewItem
Implements IDictionaryEnumerator

Private ListItemEntry As DictionaryEntry
Private enumerator As IEnumerator

Public Sub New()
enumerator = MyBase.SubItems.GetEnumerator
End Sub

Public Property NodeKey() As String
Get
Return ListItemEntry.Key.ToString()
End Get

Set(ByVal Value As String)
ListItemEntry.Key = Value
End Set
End Property

Public Property NodeValue() As Object
Get
Return ListItemEntry.Value
End Get

Set(ByVal Value As Object)
ListItemEntry.Value = Value
End Set
End Property

Public Overridable Overloads ReadOnly Property Entry() As DictionaryEntry _
Implements IDictionaryEnumerator.Entry

Get
Return ListItemEntry
End Get
End Property

Public Overridable Overloads Function MoveNext() As Boolean _
Implements IDictionaryEnumerator.MoveNext

Dim Success As Boolean

Success = enumerator.MoveNext()
Return Success
End Function

Public Overridable Overloads ReadOnly Property Current() As Object _
Implements IEnumerator.Current

Get
Return enumerator.Current
End Get
End Property

Public Overridable Overloads ReadOnly Property Key() As Object _
Implements IDictionaryEnumerator.Key

Get
Return ListItemEntry.Key
End Get
End Property

Public Overridable Overloads ReadOnly Property Value() As Object _
Implements IDictionaryEnumerator.Value

Get
Return ListItemEntry.Value
End Get
End Property

Public Overridable Overloads Sub Reset() _
Implements IEnumerator.Reset

enumerator.Reset()
End Sub
End Class

[Pirate]

Very easy way ...

If listbox.Items.Count = 0 Then
listbox.Items.AddRange(fields)
Else
Exit Sub
End If

[qpabani]

is there another way? is it possible to add all the items first, and then check for duplicates and remove them after?

[Pirate]

Originally posted by qpabani
is there another way? is it possible to add all the items first, and then check for duplicates and remove them after?

Hmmm , have you tried that code I posted , I did the trick for me ?

[qpabani]

what is fields?

[Pirate]

Originally posted by qpabani
what is fields?

Uh..that's array of returned rows . How are you populating the listbox ?

[qpabani]

List1.Items.Add("Hello")
        List1.Items.Add("Hello")
        List1.Items.Add("Hello")
 
        If ListBox1.Items.Count = 0 Then
            ListBox1.Items.AddRange(List1.Items)
        Else
            Exit Sub
        End If

doesnt work, it adds hello 3 times tothe second box..

in my program, im just adding items from data retrieved on a webpage, no arrays invovled..

[Pirate]

I know it won't work the way you have done it , rather you can do it this way :

Dim Arry() as String ={"item1","item2","item"}
 
        If ListBox1.Items.Count = 0 Then
            ListBox1.Items.AddRange(Arry)
        Else
        Exit Sub
        End If

[Edneeis]

Try explaining more about where the data is coming from or how it is collected. The best way is not to put duplicate info into the listbox, but if its already there then you have to write a routine to find and delete dupes. I'd make use of the Contains method of the items collection before putting an item in.

[qpabani]

well.. the app retrieves data from numerous pages, parses the html and adds items to the listbox.. after its done this routine, i need to be able to remove the duplicates...

anyone know how?

[Edneeis]

Instead of just adding them all in, before one is added check if it is already there, this is by far the easiest most efficent way.

'assuming these are strings and one is assigned to the item variable
If Not Listbox1.items.Contains(item) then
    Listbox1.items.Add(item)
End If

[theonetrueace]

edit....nm im just gonna setup a loop threw to look for dups

AcE

[shutty]

I agree with Edneeis, check the list before adding items rather than add them then delete duplicates.

[theonetrueace]

well heres a lil loop code i cam up with.....its very lame and there is something wrong...i cant put my fingure on it...tell me wut u think....this is ofcourse ran after the id is added....

Private Sub RunDupCheck()
        If LV_IDList.Items.Count <> 0 Then
            Dim i As Integer = LV_IDList.Items.Count - 1
            Dim ii As Integer = LV_IDList.Items.Count - 1
            Do Until i = -1
                Do Until ii = -1
                    If i <> ii Then
                        If LV_IDList.Items(ii).Text = LV_IDList.Items(i).Text Then
                            LV_IDList.Items(ii).Remove()
                        End If
                        ii = ii - 1
                    Else
                        ii = ii - 1
                    End If
                Loop
                i = i - 1
            Loop
        End If
    End Sub

AcE

[Evad]

Just like Edneeis stated, but this checks the text value.

  Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
    If ListBox.Items.IndexOf("Hello World") = -1 Then
      ListBox.Items.Add("Hello World")
    Else
      MsgBox("Item - Hello World already exists")
    End If
  End Sub

[shutty]

There are a couple of obvious problems, firstly when you would need to reset the 'ii' count before attempting to do the second loop again and when you remove an item from the list all the indexes are shifted by one, so 'i' can point to an item that no longer exists.

This seems to work, tho I've not compiled and run it!

        Dim i as integer
        Dim ii as integer

        i = 0
        Do While i < LV_IDList.Items.Count
            ii = i + 1
            Do While ii < LV_IDList.Items.Count
                If LV_IDList.Items(i).Text = LV_IDList.Items(ii).Text Then
                    LV_IDList.Items(ii).Remove()
                Else
                    ii += 1
                End If
            Loop
            i += 1
        Loop