title: How to show/hide a UIView with animation in iOS?
body: <p>The main UIView contains two subviews - <code>UIView_1</code> and <code>UIView_2</code>.<br>
  In the <code>UIView_2</code>, there is a button to show or hide the <code>UIView_1</code>.<br>
  For example, when a user touches the button to show the <code>UIView_1</code>, then <strong><code>UIView_1</code> will slide down and <code>UIView_2</code> will push downwards with transition</strong>.<br>
  I have very little knowledge in animation. Can someone show me some sample code for reference?<br>
  Should I use CGAffineTransformMakeTranslation?<br>
  Thanks.<img src="https://i.stack.imgur.com/Ynm8F.png" alt="enter image description here"></p>