title: How can i know which button is clicked? Objective C
body: <p>I am doing Presence1 in Assignment which require me builds a multiple screens application.
  I have two ViewController, vc1 and vc2. In vc1, i have two buttons. I use a same method for them and the title of them are same.</p>
  
  <p>My question is How can i know which button is clicked in vc1 when i change to vc2? </p>
  
  <p>There are a topic show me that I should get positions (x,y) of mouse when i click on button, but i think it is not quite good.</p>