Question

I am able to only move single items from one listbox to another with this code. I tried with both MultiSimple & MultiExtended SelectionMode.

How do I select multiple items and then move them?

Private Sub cmdAdd_Click(ByVal sender As System.Object, 
                         ByVal e As System.EventArgs
                        ) Handles cmdAdd.Click

        Dim i As Integer = Listbox1.SelectedIndex

        If i = -1 Then
            Exit Sub 'skip if no item is selected
        End If

        Listbox2.Items.Add(Listbox1.Items(i)) 
        Listbox1.Items.RemoveAt(i)

    End Sub

Answer 1

You need to use SelectedIndices or SelectedItems.

Private Sub cmdAdd_Click(ByVal sender As System.Object, 
                         ByVal e As System.EventArgs
                        ) Handles cmdAdd.Click

    Dim selectedItems = (From i In ListBox1.SelectedItems).ToArray()

    For Each selectedItem In selectedItems

        Listbox2.Items.Add(selectedItem)
        Listbox1.Items.Remove(selectedItem)

    Next

End Sub

Note the use of a Linq query to get list of selected items as an array. Using an array is required to prevent “Collection changed” exceptions. You may need to add a reference to System.Linq.