title: viewdidappear is not called from tab bar controller
body: <p>I have a <code>TabBarController</code> with <code>NavigationController</code>... the main <code>TabController</code> has some buttons which i want to add borders to... am doing this in <code>ViewDidAppear</code> but its not called! when i go to child controller and click back button its called now .. but when firstly click the tab is not called!</p>
  
  <p>and what am doing is this in the main tab vc:</p>
  
  <pre><code>  override func viewDidAppear(_ animated: Bool) {
      super.viewDidAppear(animated)
  
      if MOLHLanguage.isArabic(){
          aboutusbtn.addRightBorderHome( borderWidth: 3)
          rulesbtn.addRightBorderAboutus(borderWidth: 3)
          committeebtn.addRightBorderHistory(borderWidth: 3)
          generalbtn.addRightBorderShare(borderWidth: 3)
          publickbtn.addRightBorderHome(borderWidth: 3)
          contactusbtn.addRightBorderAboutus(borderWidth: 3)
      }else{
          aboutusbtn.addLeftBorderHome(width: 3)
          committeebtn.addLeftBorderAboutus(width: 3)
          rulesbtn.addLeftBorderHistory(width: 3)
          generalbtn.addLeftBorderShare(width: 3)
          publickbtn.addLeftBorderHome(width: 3)
          contactusbtn.addLeftBorderAboutus(width: 3)
      }
  }
  </code></pre>
  
  <p>but this is not called until i click back from child ... but when first click on the tab it will not be called!</p>
  
  <p>why? and how to solve this?</p>
  
  <p><img src="https://i.stack.imgur.com/KUtc3.png" width="450" height="700"/></p>