title: Launch an activity only once after Install
body: <p>I have QR scanner app. There are 3 activities in the app. </p>
  
  <p>1) Main activity - Button to open camera and start scanning</p>
  
  <p>2) QR activity - Scan a QR code</p>
  
  <p>3) Web Activity - On successful scanning, open a web page in the app</p>
  
  <p>Here, the Main activity and QR activity should only launch once, only after the initial install. I read somewhere about using shared preferences. But I am a little confused as to where do I check the variable, as in which activity. Should I check my shared variable in the Main Activity? </p>
  
  <p>This is my first app. Sorry if this is a silly doubt.</p>