title: How to add "advertisements" in the UIScrollView like BBC News app?
body: <p>I have created the news app which use the "UIScrollView + UIWebView" to let users to swipe  through different news. However, I would like to ask whether it's possible for me to add the advertisements like the BBC News app or not, which users will see the advertisements while scrolling horizontally.</p>
  
  <p><img src="https://i.stack.imgur.com/rIlw7.png" alt="enter image description here"></p>
  
  <p><img src="https://i.stack.imgur.com/lVCCE.png" alt="enter image description here"></p>
  
  <p>I was trying to use addSubView while scrolling (scrollViewDidScroll) but it replaces the existing content. </p>
  
  <p>I realize BBC News app do the things like this,</p>
  
  <p>Users swipe through the news --> After swiping a few times --> show the ads (in position 5, for instance) --> users swipe from start to the end again --> the ads appear again, but this time could be in position 3). </p>
  
  <p>But I just don't know how to make it work for my app. Any clue? thanks in advance.</p>