Not sure what you are trying to do, but this might get you started:
Private Sub UserForm_Initialize()
Dim arrItems() As String
Dim bRB As MSForms.ReturnBoolean
  arrItems = Split("Apples|Oranges|Peaches|Pears", "|")
  ListBox1.List = arrItems
  ListBox1.Selected(2) = True
  ListBox1_DblClick bRB
End Sub

Private Sub ListBox1_DblClick(ByVal Cancel As MSForms.ReturnBoolean)
Dim lngIndex As Long
  For lngIndex = 0 To ListBox1.ListCount - 1
    If ListBox1.Selected(lngIndex) Then
      TextBox1.Text = ListBox1.List(lngIndex)
      Exit For
    End If
  Next lngIndex
End Sub
Note the CANCEL will not function in this case.