visual basic List.box question - vb.net

Question

i have 1 text box and 1 listbox in my VB form.
i want to check duplicate item,compare with textbox.text1 and listbox.list item.
and if textbox.text1 value is '3333' and listbox.list multiple value is '1111' '2222' '3333' '4444'
so how to implement such like duplicate check routine?
so if duplicate detect compare with current text1 value and compare with one of listbox's
value is if detect,want to popup messagebox
thanks in advance

Answer 1

Assuming you are inserting strings into your ListBox you can do this:
Private Sub button1_Click(ByVal sender As Object, ByVal e As EventArgs) Handles Button1.Click
Dim x As String
For Each x In ListBox1.Items
If (x = TextBox1.Text) Then
MessageBox.Show("Error")
Return
End If
Next
ListBox1.Items.Add(TextBox1.Text)
End Sub
If it's another type of object that has a property called Value then you need a small change:
Private Sub button1_Click(ByVal sender As Object, ByVal e As EventArgs) Handles Button1.Click
Dim x As Foo
For Each x In ListBox1.Items
If (x.Value = TextBox1.Text) Then
MessageBox.Show("Error")
Return
End If
Next
ListBox1.Items.Add(TextBox1.Text)
End Sub

Answer 2

Assuming that the ListBox contains strings, you can use the Contains method of the Items collection to check for matches. Example (make a form with a ListBox called '_theListBox', a TextBox called '_theTextBox' and a Label called '_theLabel'):
Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
_theListBox.Items.AddRange(New String() {"aaaa", "bbbb", "cccc", "dddd"})
End Sub
Private Sub _theTextBox_TextChanged(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles _theTextBox.TextChanged
If ListBoxContainsItem(_theListBox, _theTextBox.Text) Then
_theLabel.Text = "It's a match"
Else
_theLabel.Text = ""
End If
End Sub
Private Function ListBoxContainsItem(ByVal lb As ListBox, ByVal text As String) As Boolean
' check if the string is present in the list '
Return lb.Items.Contains(text)
End Function