title: preventing from re-navigating after pop, in onObserve?
body: <p>I'm using MVVM + Retrofit + navigation in my new project and calling retrofit from the repository. Now when I receive a response in fragment-A with liveData, I navigate to next fragment-B, everything looks good so far. The problem starts from where in fragment-B I want to pop to the previous fragment and edit something.</p>
  
  <p>In previous fragment(fragment-A) as soon as init, onObserve is called and navigates to fragment-B again!</p>
  
  <p>some solutions came to my mind that worked, like:<br></p>
  
  <ol>
  <li>setValue(null) after navigate to fragment-B<br></li>
  <li>Remove observe in onCreateView and observe it when call retrofit from repository(This solution creates other problems)<br>
  and Etc.</li>
  </ol>
  
  <pre><code>  override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
          super.onViewCreated(view, savedInstanceState)
  
          // fetch data from server
          viewModel.articles.observe(viewLifecycleOwner) {
  
              //if it was success
              findNavController().navigate(R.id.fragment_a_to_fragment_b)
  
  
              }
      }
  </code></pre>