Visual Basic List Box

[FaiL___]

So I am taking computer science and we need to create a 2 list boxes that will transfer an item from one to the other and then be able to delete from the second list box. I have done that, but want to make sure that someone cannot add an item twice, which they can at the minute. Any way?

[Mr_KoKa]

Just loop through items on the list and check if they're equal, if you find same item on the list then interrupt execution of adding function, if item hasn't been found add it.

 

For Each item As String In ListBox1.Items
  If item = TextBox1.Text Then
    MessageBox.Show("Item " + TextBox1.Text + " is already on the list.")
    Return
  End If
Next

ListBox1.Items.Add(TextBox1.Text)

You can implement it when you add new item on first listbox, and also when you copy items from one to the another, or you can check in both listboxes in first place then you don't need to check it again when copying.

[FaiL___]

1 hour ago, Mr_KoKa said:

Just loop through items on the list and check if they're equal, if you find same item on the list then interrupt execution of adding function, if item hasn't been found add it.

 

For Each item As String In ListBox1.Items
  If item = TextBox1.Text Then
    MessageBox.Show("Item " + TextBox1.Text + " is already on the list.")
    Return
  End If
Next

ListBox1.Items.Add(TextBox1.Text)

You can implement it when you add new item on first listbox, and also when you copy items from one to the another, or you can check in both listboxes in first place then you don't need to check it again when copying.

Cheers, I think I understand now, but I wouldn't be able to do the last bit that you suggested as it the first list is populated before runtime and the user selects items from the list and adds them to the second list box, but keeping them present in the first list box. The trouble is you can copy the same item twice into the second list box

[Mr_KoKa]

Ok, I thought you populate first listbox on runtime and then you move all to the second one.

When you move one item from first listbox you probably use code that looks like this:

 

If ListBox1.SelectedIndex != -1 Then
	ListBox2.Items.Add(ListBox1.Items(ListBox1.SelectedIndex))
End If

You can just assign item you want to move to variable and compare existing items against it.

If ListBox1.SelectedIndex != -1 Then
        Dim newItem As String = ListBox1.Items(ListBox1.SelectedIndex)

        For Each item As String In ListBox2.Items
            If item = newItem Then
                MessageBox.Show("Item " + newItem + " is already on the list.")
                Return
            End If
        Next

        ListBox2.Items.Add(newItem)
End If