title: What is the difference between src and background of ImageView
body: <p>I am a puzzled about using <code>src</code> or <code>background</code> for an <code>ImageView</code>.</p>
  
  <p>I know the former means the content of this <code>ImageView</code> and the latter means the background of the <code>ImageView</code>. </p>
  
  <p>But how to decide which one to use? I don't see the difference.</p>