title: How to implement android Toolbar Back button
body: <p>I am using a custom toolbar. I need to add back button to it. Now I am using this code to add the back button.</p>
  
  <pre><code>Toolbar toolbar = (Toolbar) getActivity().findViewById(R.id.toolbar);
          toolbar.setBackgroundColor(getResources().getColor(R.color.white));
          toolbar.setNavigationIcon(getResources().getDrawable(R.drawable.back_arrow));
          toolbar.setNavigationOnClickListener(new View.OnClickListener() {
              @Override
              public void onClick(View v) {
                  onBackPressed();
              }
          });
  </code></pre>
  
  <p>This works fine. I can see the back button added. But consider the case where I am in Fragment1 which has no back button. Now I move to Fragment2 and I add in Back Button. From Fragment 2 I open Fragment 3 and I add the back button again. </p>
  
  <p>Now when I press back button from fragment3 to go back to fragment2  i have to check the Fragment Stack to see whether the back button is required in fragment 2 or not.</p>
  
  <p>Is there any other way to handle back button automatically as we push fragments to stack?</p>