Handling back button in Android Navigation Component

Question

I d like to know how properly handle system back button action using Navigation Controller  In my app I have two fragments  for ex  fragment1 and fragment2  and I have an action in fragment1 with destination to fragment2  Everything works well except one thing - when user presses system back button in fragment2 I want to show a dialog  using DialogFragment for example  to confirm exit  What is the best way to implement this behavior  If I use app defaultNavHost  true  in my host fragment then it automatically goes back ignoring my rules  And  additionally  what is this component for     Should I use  pop to  may be

User · Answer

Use this if you re using fragment or add it in your button click listener  This works for me  requireActivity   onBackPressed    Called when the activity has detected the user s press of the back key  The getOnBackPressedDispatcher   OnBackPressedDispatcher  will be given chance to handle the back button before the default behavior of android app Activity onBackPressed    is invoked

User · Answer

I need to support both real back button and toolbar back button with ability to override  quot Back quot  click in both cases  to show dialog or something else   I made an additional method in activity and corresponding boolean checks   onBackPressed  in my case  in fragments     Process hardware Back button override fun onBackPressed         if  canCloseActivity              super onBackPressed               Process toobar Back and Menu button override fun onSupportNavigateUp    Boolean       if  canCloseActivity              return navController navigateUp appBarConfiguration     super onSupportNavigateUp             return false       Do real check if has unfinished tasks  return false to override activity closing private fun canCloseActivity    Boolean       val currentFragment   navHostFragment childFragmentManager primaryNavigationFragment      return when           currentFragment is MyFragment  amp  amp  currentFragment onBackPressed   - gt  false          drawerLayout isOpen - gt                drawerLayout close               false                   fullScreenPreviewLayout visibility    View VISIBLE - gt                closeFullscreenPreview               false                   else - gt  true

User · Answer

If you use Navigation Component follow the codes below in your onCreateView   method  in this example I want just to close my app by this fragment    OnBackPressedCallback backPressedCallback   new OnBackPressedCallback true             Override         public void handleOnBackPressed                 new AlertDialog Builder Objects requireNonNull getActivity                          setIcon R drawable icon 01                       setTitle getResources   getString R string close app title                        setMessage getResources   getString R string close app message                        setPositiveButton R string yes  new DialogInterface OnClickListener                              Override                         public void onClick DialogInterface dialog  int which                                getActivity   finish                                                                          setNegativeButton R string no  null                       show                         requireActivity   getOnBackPressedDispatcher   addCallback this  backPressedCallback

User · Answer

A little late to the party  but with the latest release of Navigation Component 1 0 0-alpha09  now we have an AppBarConfiguration OnNavigateUpListener   Refer to these links for more information   https   developer android com reference androidx navigation ui AppBarConfiguration OnNavigateUpListener https   developer android com jetpack docs release-notes

User · Answer

My Opinion  requireActivity   onBackPressed    requireActivity   onBackPressed

User · Answer

Newest Update - April 25th  2019 New release androidx activity ver  1 0 0-alpha07 brings some changes More explanations in android official guide  Provide custom back navigation Example  public class MyFragment extends Fragment         Override     public void onCreate  Nullable Bundle savedInstanceState            super onCreate savedInstanceState               This callback will only be called when MyFragment is at least Started          OnBackPressedCallback callback   new OnBackPressedCallback true    enabled by default                    Override             public void handleOnBackPressed                        Handle the back button event                                  requireActivity   getOnBackPressedDispatcher   addCallback this  callback               The callback can be enabled or disabled here or in handleOnBackPressed                    Old Updates UPD  April 3rd  2019 Now its simplified  More info here Example  requireActivity   getOnBackPressedDispatcher   addCallback getViewLifecycleOwner    this     Override public boolean handleOnBackPressed           Do your job here       use next line if you just need navigate up       NavHostFragment findNavController this  navigateUp           Log e getClass   getSimpleName     quot handleOnBackPressed quot        return true         Deprecated  since Version 1 0 0-alpha06 April 3rd  2019    Since this  it can be implemented  just using JetPack  implementation OnBackPressedCallback in your fragment and add it to activity  getActivity   addOnBackPressedCallback getViewLifecycleOwner   this   Your fragment should looks like this  public MyFragment extends Fragment implements OnBackPressedCallback         Override     public void onActivityCreated  Nullable Bundle savedInstanceState            super onActivityCreated savedInstanceState                    getActivity   addOnBackPressedCallback getViewLifecycleOwner   this               Override     public boolean handleOnBackPressed               Do your job here           use next line if you just need navigate up           NavHostFragment findNavController this  navigateUp               Log e getClass   getSimpleName     quot handleOnBackPressed quot            return true              Override     public void onDestroyView             super onDestroyView            getActivity   removeOnBackPressedCallback this            UPD  Your activity should extends AppCompatActivityor FragmentActivity and in Gradle file   implementation  androidx appcompat appcompat  lastVersion

User · Answer

Depending on your logic  if you want to close only the current fragment you have to pass viewLifecycleOwner  code is shown below      requireActivity   onBackPressedDispatcher addCallback viewLifecycleOwner  object   OnBackPressedCallback true            override fun handleOnBackPressed                 requireActivity   finish                      However  if you want to close application on backPressed no matter from what fragment probably you wouldn t want that    don t pass the viewLifecycleOwner  Also if you want to disable the back button  do not do anything inside the handleOnBackPressed    see below    requireActivity   onBackPressedDispatcher addCallback viewLifecycleOwner  object   OnBackPressedCallback true            override fun handleOnBackPressed                    do nothing it will disable the back button

User · Answer

And if you want the same behavior also for the toolbar back button just add this in your activity    Override public boolean onOptionsItemSelected MenuItem item        if  item getItemId      android R id home            getOnBackPressedDispatcher   onBackPressed            return true            return super onOptionsItemSelected item

User · Answer

The recommended approach is to add an OnBackPressedCallback to the activity s OnBackPressedDispatcher   requireActivity   onBackPressedDispatcher addCallback viewLifecycleOwner            handle back event

User · Answer

I written in main activity like this   override fun onSupportNavigateUp    Boolean           return findNavController R id my nav host fragment  navigateUp appBarConfiguration

User · Answer

Here is solution that should do what you want  but i think it is a bad solution  because it is going against Android Navigation component idea letting the android handle the navigation    Override  onBackPressed  inside your activity  override fun onBackPressed         when NavHostFragment findNavController nav host fragment  currentDestination id            R id fragment2- gt                val dialog AlertDialog Builder this  setMessage  Hello   setPositiveButton  Ok   DialogInterface OnClickListener   dialogInterface  i - gt                  finish                  show                     else - gt                super onBackPressed

User · Answer

The recommended method worked for me but after updating my library implementation  androidx appcompat appcompat 1 1 0    Implement as below   val onBackPressedCallback   object   OnBackPressedCallback true            override fun handleOnBackPressed                    Handle the back button event                     requireActivity   onBackPressedDispatcher addCallback this  onBackPressedCallback    using Kotlin

User · Answer

In 2 1 0-alpha06  If you want to handle backpress only in current fragment  requireActivity   onBackPressedDispatcher addCallback this LoginFragment           handle back event     For whole Activity  requireActivity   onBackPressedDispatcher addCallback            handle back event

User · Answer

Here is my solution  Use androidx appcompat app AppCompatActivity for the activity that contains the NavHostFragment fragment   Define the following interface and implement it in all navigation destination fragments  interface InterceptionInterface        fun onNavigationUp    Boolean     fun onBackPressed    Boolean     In your activity override onSupportNavigateUp and onBackPressed   override fun onSupportNavigateUp    Boolean           return getCurrentNavDest   onNavigationUp      navigation host fragment findNavController   navigateUp      override fun onBackPressed             if   getCurrentNavDest   onBackPressed                 super onBackPressed                private fun getCurrentNavDest    InterceptionInterface           val currentFragment   navigation host fragment childFragmentManager primaryNavigationFragment as InterceptionInterface         return currentFragment     This solution has the advantage  that the navigation destination fragments don t need to worry about the unregistering of their listeners as soon as they are detached

User · Answer

you can provide your custom back navigation by using OnBackPressedDispatcher  class MyFragment   Fragment      override fun onCreate savedInstanceState  Bundle         super onCreate savedInstanceState          This callback will only be called when MyFragment is at least Started      val callback   requireActivity   onBackPressedDispatcher addCallback this               Handle the back button event    and if you want to need navigate up   NavHostFragment findNavController this  navigateUp                 The callback can be enabled or disabled here or in the lambda       More explanations in android official guide  https   developer android com guide navigation navigation-custom-back

User · Answer

I have searched through many threads and none of them work  Finally I found one  MainActivity java  Override protected void onCreate Bundle savedInstanceState        super onCreate savedInstanceState       setContentView R layout activity main        Toolbar mToolbar   findViewById R id topAppBar       setSupportActionBar mToolbar       Override public boolean onSupportNavigateUp         navController navigateUp        return super onSupportNavigateUp       MyFragment java  Override public void onViewCreated  NonNull final View view   Nullable Bundle savedInstanceState        Toolbar mToolbar    MainActivity  getActivity   findViewById R id topAppBar       mToolbar setNavigationOnClickListener new View OnClickListener              Override         public void onClick View v                   Do something when uses presses back button  showing modals  messages                     Note that this will override behaviour of back button                       Override public void onStop            Reset back button to default behaviour when we leave this fragment     Toolbar mToolbar    MainActivity  getActivity   findViewById R id topAppBar       mToolbar setNavigationOnClickListener new View OnClickListener              Override         public void onClick View v                mainActivity onBackPressed                           super onStop

User · Answer

This is 2 lines of code can listen for back press  from fragments   TESTED and WORKING     requireActivity   getOnBackPressedDispatcher   addCallback getViewLifecycleOwner    new OnBackPressedCallback true             Override         public void handleOnBackPressed                    setEnabled false      call this to disable listener               remove       call to remove listener               Toast makeText getContext     Listing for back press from this fragment   Toast LENGTH SHORT  show

User · Answer

For anyone looking for a Kotlin implementation see below   Note that the OnBackPressedCallback only seems to work for providing custom back behavior to the built-in software hardware back button and not the back arrow button home as up button within the actionbar toolbar   To also override the behavior for the actionbar toolbar back button I m providing the solution that s working for me   If this is a bug or you are aware of a better solution for that case please comment   build gradle      implementation  androidx appcompat appcompat 1 1 0-rc01  implementation  androidx navigation navigation-fragment-ktx 2 0 0  implementation  androidx navigation navigation-ui-ktx 2 0 0        MainActivity kt      import androidx appcompat app AppCompatActivity      class MainActivity   AppCompatActivity         override fun onCreate savedInstanceState  Bundle             setContentView R layout activity main                        val navController   findNavController R id nav host fragment          val appBarConfiguration   AppBarConfiguration navController graph              This line is only necessary if using the default action bar          setupActionBarWithNavController navController  appBarConfiguration              This remaining block is only necessary if using a Toolbar from your layout          val toolbar   findViewById lt Toolbar gt  R id toolbar          toolbar setupWithNavController navController  appBarConfiguration             This will handle back actions initiated by the the back arrow             at the start of the toolbar          toolbar setNavigationOnClickListener                  Handle the back button event and return to override                 the default behavior the same way as the OnBackPressedCallback                 TODO reason  handle custom back behavior here if desired                   If no custom behavior was handled perform the default action              navController navigateUp appBarConfiguration     super onSupportNavigateUp                                   If using the default action bar this must be overridden         This will handle back actions initiated by the the back arrow         at the start of the action bar              override fun onSupportNavigateUp    Boolean              Handle the back button event and return true to override             the default behavior the same way as the OnBackPressedCallback             TODO reason  handle custom back behavior here if desired               If no custom behavior was handled perform the default action          val navController   findNavController R id nav host fragment          return navController navigateUp appBarConfiguration     super onSupportNavigateUp             MyFragment kt      import androidx activity OnBackPressedCallback import androidx fragment app Fragment      class MyFragment   Fragment         override fun onCreate savedInstanceState  Bundle             super onCreate savedInstanceState          val onBackPressedCallback   object   OnBackPressedCallback true                override fun handleOnBackPressed                        Handle the back button event                                 requireActivity   getOnBackPressedDispatcher   addCallback this  onBackPressedCallback            The official documentation can be viewed at https   developer android com guide navigation navigation-custom-back

User · Answer

Just add these lines      override fun onBackPressed                 if navController popBackStack   not                    Last fragment  Do your operation here              finish          navController popBackStack    will just pop your fragment if this is not your last fragment

User · Answer

So  I created an interface  public interface OnBackPressedListener       void onBackPressed        And implemented it by all fragments that need to handle back button  In main activity I overrided onBackPressed   method     Override public void onBackPressed         final Fragment currentFragment   mNavHostFragment getChildFragmentManager   getFragments   get 0       final NavController controller   Navigation findNavController this  R id nav host fragment       if  currentFragment instanceof OnBackPressedListener            OnBackPressedListener  currentFragment  onBackPressed        else if   controller popBackStack            finish         So  If the top fragment of my Navigation host implements OnBackPressedListener interface  I call its onBackPressed   method  elsewhere I simply pop back stack and close application if the back stack is empty

User · Answer

just create an extension function to the fragment fun Fragment onBackPressedAction action     - gt  Boolean        requireActivity   onBackPressedDispatcher addCallback viewLifecycleOwner  object           OnBackPressedCallback true            override fun handleOnBackPressed                 this isEnabled   action               if   this isEnabled                    requireActivity   onBackPressed                                     and after in the fragment put the code into onCreateView  the action must return false to call the activity onBackPressed  onBackPressedAction     do something

User · Answer

If you are using BaseFragment for your app then you can add onBackPressedDispatcher to your base fragment     Make a BaseFragment for all your fragments abstract class BaseFragment   Fragment      private lateinit var callback  OnBackPressedCallback         SetBackButtonDispatcher in OnCreate      override fun onCreate savedInstanceState  Bundle         super onCreate savedInstanceState      setBackButtonDispatcher             Adding BackButtonDispatcher callback to activity     private fun setBackButtonDispatcher         callback   object   OnBackPressedCallback true            override fun handleOnBackPressed                 onBackPressed                       requireActivity   onBackPressedDispatcher addCallback this  callback            Override this method into your fragment to handleBackButton       open fun onBackPressed              Override onBackPressed   in your fragment by extending basefragment    How to use this into your fragment class MyFragment     BaseFragment     private lateinit var mView  View  override fun onCreateView inflater  LayoutInflater  container  ViewGroup   savedInstanceState  Bundle    View        mView   inflater inflate R layout fragment my  container  false      return mView rootView    override fun onBackPressed           Write your code here on back pressed

User · Answer

I tried Jurij Pitulja solution but I just wasn t able to find getOnBackPressedDispatcher or   addOnBackPressedCallback also using Kiryl Tkach s solution wasn t able to find the current fragment  so here s mine   interface OnBackPressedListener       fun onBackPressed    Boolean    override fun onBackPressed         val navHostFragment   supportFragmentManager findFragmentById R id nav host fragment      val currentFragment   navHostFragment  childFragmentManager   fragments 0      if  currentFragment  is OnBackPressedListener      currentFragment as OnBackPressedListener  onBackPressed    super onBackPressed     this way you can decide in fragment whether the activity should take control of back pressed or not   Alternatively  you have BaseActivity for all your activities  you can implement like this  override fun onBackPressed         val navHostFragment   supportFragmentManager findFragmentById R id nav host fragment      if  navHostFragment    null           val currentFragment   navHostFragment childFragmentManager fragments 0          if  currentFragment  is AuthContract OnBackPressedListener                      currentFragment as AuthContract OnBackPressedListener  onBackPressed    super onBackPressed         else           super onBackPressed

User · Answer

Try this  I think this will help you   override fun onBackPressed         when  mNavController getCurrentDestination     getId               R id loginFragment - gt                onWarningAlertDialog this   Alert    Do you want to close this application                       R id registerFragment - gt                super onBackPressed                        private fun onWarningAlertDialog mainActivity  MainActivity  s  String  s1  String             val dialogBuilder   AlertDialog Builder this          dialogBuilder setMessage       s1                   setCancelable false                   setPositiveButton  Proceed   DialogInterface OnClickListener   dialog  id - gt                      finish                                       setNegativeButton  Cancel   DialogInterface OnClickListener   dialog  id - gt                      dialog cancel                                  create dialog box         val alert   dialogBuilder create              set title for alert dialog box         alert setTitle  AlertDialogExample              show alert dialog         alert show

[android] Handling back button in Android Navigation Component

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