title: How to choose default option in NSComboBox or NSPopUpButton?
body: <p>I'm developing a Mac OS App using Xcode 10 and Swift 4.2. </p>
  
  <p>For a particular scenario, I want to provide the users with are four options but for most users the first option is enough. So I want the first option to be default and when the user wants to change, he can choose from the other three. 
  I'm trying to achieve the same using NSComboBox or NSPopUpButton but I'm struck.</p>
  
  <p>In the below image, the first is a combo box and the next is a popup button. </p>
  
  <p><a href="https://i.stack.imgur.com/Ndxo0.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/Ndxo0.png" alt="Combo Box and Pop Up Button"></a></p>
  
  <p>If the user clicks on "Default", I need to call a method. If the user Clicks on the arrow mark, I need to display the list of options, the user will select one option and then I have to call the same method. </p>
  
  <p>Below is the image showing list of options, if arrow is clicked. </p>
  
  <p><a href="https://i.stack.imgur.com/p9eJd.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/p9eJd.png" alt="Combo box showing options"></a></p>
  
  <p>The problem is that ComboBox inherits from NSControl but when I set action to it, the method call is not working and PopUpButton lists the options, irrespective of whether I click on "Default" label or on the arrow. </p>
  
  <p>The main objective is that, it should be only one mouse click by the user to choose the default option and two clicks to change the option. 
  How to achieve it using ComboBox, PopUpButton or any other object?</p>