title: How to set button click effect in Android?
body: <p>In Android, when I set a background image to a button, I can not see any effect on it when it's clicked.</p>
  <p>I need to set some effect on the button, so the user can recognise that the button is clicked.</p>
  <p>The button should be dark for a few seconds when it is clicked. How to do this?</p>