Hello,

i have 3 listboxes on my screen..
A listbox with emails from datasource A, a listbox with emails from datasource B and an empty listbox

i want in the empty listbox the emails that are in A but not in B

i've got this but it doesn't put any emails in the listbox...


For k As Integer = lsbSQL.Items.Count - 1 To 0 Step -1
If lsbAccess.Items.Contains(lsbSQL.Items(k)) Then
MessageBox.Show("Item Found")
lsbVerschil.Items.Add(lsbSQL.Items(k))
Else
MessageBox.Show("Item Not Found")
End If
Next

Actually your code does the opposite thing. It adds to third list box items from list box A that do exist in list box B. Otherwise, there's nothing wrong with your code.

Here's your code (list boxes renamed)

ListBox1.Items.Add("first@acme.com")
ListBox1.Items.Add("second@acme.com")
ListBox2.Items.Add("second@acme.com")
ListBox2.Items.Add("third@acme.com")

For k As Integer = ListBox1.Items.Count - 1 To 0 Step -1
  If Not ListBox2.Items.Contains(ListBox1.Items(k)) Then
    MessageBox.Show("Item Found")
    ListBox3.Items.Add(ListBox1.Items(k))
  Else
    MessageBox.Show("Item Not Found")
  End If
Next

Only change is the test If Not ListBox2.Items.Contains(ListBox1.Items(k)) Then The code works just fine...

thanks... but the problem is in the 3rd listbox there comes:system.data.datarowview and not the text

You mean you get the text "system.data.datarowview" to the third list box?

You could try an explicit conversion of a list box item to a string

ListBox1.Items.Add("first@acme.com")
ListBox1.Items.Add("second@acme.com")
ListBox2.Items.Add("second@acme.com")
ListBox2.Items.Add("third@acme.com")


For k As Integer = ListBox1.Items.Count - 1 To 0 Step -1
  If Not ListBox2.Items.Contains(ListBox1.Items(k)) Then
    MessageBox.Show("Item Found")
    Dim TempStr As String
    TempStr = CStr(ListBox1.Items.Item(k))
    ListBox3.Items.Add(TempStr)
  Else
    MessageBox.Show("Item Not Found")
  End If
Next

Does that help anything?

this is what is in my form load...
Dim blnConGelukt As Boolean
blnConGelukt = mycon.funConEmp()
myacc.fstudenten()
Me.lsbAccess.DataSource = myacc.p_mydv.ToString
Me.lsbAccess.DisplayMember = "Email"
Me.lsbAccess.ValueMember = "Id"
Me.lsbSQL.DataSource = mycon.p_datav.ToString
Me.lsbSQL.DisplayMember = "StudentPrivéEmail"
Me.lsbSQL.ValueMember = "StudentId"

now when i click on a button

For k As Integer = lsbSQL.Items.Count - 1 To 0 Step -1

If Not lsbAccess.Items.Contains(lsbSQL.Items(k)) Then

MessageBox.Show("Item Found")

Dim TempStr As String

TempStr = CStr(lsbSQL.Items.Item(k))

lsbVerschil.Items.Add(TempStr)

Else

MessageBox.Show("Item Not Found")

End If

Next

but i get the following error:

De conversie van type DataRowView naar type String is ongeldig.
The conversion from typ Datarowview to type String isn't good

Since the list boxes are databound, the comparison can't be done in a straightforward manner. You have to grab first the underlying dataview and compare items in that (and from the right column too).

Here's a rewritten version

Dim k As Integer
Dim x As Integer
Dim bFound As Boolean ' Flag if item exists
Dim TempStr As String

For x = 0 To lsbAccess.Items.Count - 1 ' Loop the first listbox
  bFound = False
  ' Loop the second listbox
  For k = 0 To lsbSQL.Items.Count - 1
    ' Compare from rows x and k the second column value (=email)
    If CType(lsbAccess.DataSource, DataView).Item(x).Item(1).ToString = CType(lsbSQL.DataSource, DataView).Item(k).Item(1).ToString Then
      ' Exists in the second listbox. Exit inner loop
      bFound = True
      Exit For
    End If
  Next k
  If Not bFound Then
    ' Item wasn't found, add item to the third box
    ' Item is taken from the row number x and second column
    TempStr = CType(lsbAccess.DataSource, DataView).Item(x).Item(1).ToString
    lsbVerschil.Items.Add(TempStr)
  End If
Next x

Notice that the comparison is case sensitive. There may be some "easier" way to do comparison but this worked. I also expected that the DataSource property is set to a dataview object. Check and change Me.lsbAccess.DataSource = myacc.p_mydv.ToString and Me.lsbSQL.DataSource = mycon.p_datav.ToString lines so that the DataSource property is a dataview object.

thanks, it works, and yes my datasource is linked to a dataview, i copied the wrong datasources

thanks a lot ! was looking for answer for week

the only thing i needed to change was lsbSQL.DataSource, DataView).Item(k).Item(1).ToString to lsbSQL.DataSource, DataView).Item(k).Item("columname").ToString

Hi! Nice to hear that you got answer to your problem. Could you please mark the thread as solved. Thank you!

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