title: How to implement the data source for multiple combo boxes in the same view controller
body: <p>I have 2 combo boxes that use the same dictionary as the data source. in the first combo box the keys will be displayed and in the second one the values will be displayed. </p>
  
  <p>First I need a bit of help with implementing the data source delegate methods; please see code listing below. the relevant boxes are floorsBox and roomsBox. Ignore the other 2 as they will be populated from a local variable or from the interface. 
  Also, lets say that for the first floor [key = 0] i have 3 rooms [value = 3], how do I take the value of 3 and make it into 3 items inside the roomsBox; So that every time the floor changes the box for the rooms has the corresponding number of items (if that makes sense). I really do appreciate your help and I thank you.</p>
  
  <pre><code>class RoomAndAlarmTypesVC: NSViewController, NSComboBoxDelegate, NSComboBoxDataSource {
  
  //MARK: - Properties
  
  private var floorsAndRooms = [String: String]()
  
  @IBOutlet private weak var floorsBox: NSComboBox!
  
  @IBOutlet private weak var roomsBox: NSComboBox!
  
  @IBOutlet private weak var roomType: NSComboBox!
  
  @IBOutlet private weak var alarmType: NSComboBox!
  
  //MARK: - Actions
  
  override func viewDidLoad() {
      super.viewDidLoad()
      floorsAndRooms = representedObject as! [String : String]
      floorsBox.usesDataSource = true
      roomsBox.usesDataSource = true
      roomType.usesDataSource = true
      alarmType.usesDataSource = true
  
      floorsBox.delegate = self
      roomsBox.delegate = self
      roomType.delegate = self
      alarmType.delegate = self
  
      floorsBox.dataSource = self
      roomsBox.dataSource = self
      roomType.dataSource = self
      alarmType.dataSource = self
  }
  @IBAction private func setTheSystem(_ sender: NSButton) {
  
  }
  
  func numberOfItems(in comboBox: NSComboBox) -&gt; Int {
      what do i do here?
  }
  
  func comboBox(_ comboBox: NSComboBox, objectValueForItemAt index: Int) -&gt; Any? {
      same here?
  }
  </code></pre>
  
  <p>}</p>