title: How to pass a variable from Activity to Fragment, and pass it back?
body: <p>I am currently making an android app, and I want to pass a date between activity and fragment.
  My activity has a button, which opens the fragment: DatePickerFragment.</p>
  
  <p>In my activity I show a date, which I want to modify with the fragment. So I want to pass the date to the datepicker, and send it back to the activity.</p>
  
  <p>I've tried a lot of solutions, but none are working. The easy way would pass an argument, but this can't be done with fragments.</p>