title: Custom image in a button in Flutter
body: <p>I'm trying to create a button which will do some action when pressed, suppose it calls a function _pressedButton() also if the user taps on it (or taps and hold), the image changes. </p>
  
  <p>Consider this like a button with a custom picture on pressed. </p>
  
  <p>In the follow-up, can I also change the image based on some external factor?
  eg. if some function A returns true, show image 1, else show image 2</p>