What is Activity finish method doing exactly

Question

I m developing android applications for a while   and followed a lot of posts about activity life cycle  and application s life cycle   I know Activity finish   method calls somewhere in the way to Activity onDestroy    and also removing the activity from stack  and I guess it somehow points to operating system and garbage collector that he can  do his trick  and free the memory when it find it a good time doing so            I came to this post -  Is quitting an application frowned upon  and read Mark Murphy s answer   It made me a bit confused about what exactly the finish   method actually does   Is there a chance I ll call finish   and onDestroy   won t be called

User · Answer

In addition to  rommex answer above  I have also noticed that finish   does queue the destruction of the Activity and that it depends on Activity priority    If I call finish   after onPause    I see onStop    and onDestroy   immediately called    If I call finish   after onStop    I don t see onDestroy   until 5 minutes later    From my observation  it looks like finish is queued up and when I looked at the adb shell dumpsys activity activities it was set to finishing true  but since it is no longer in the foreground  it wasn t prioritized for destruction    In summary  onDestroy   is never guaranteed to be called  but even in the case it is called  it could be delayed

User · Answer

onDestroy   is meant for final cleanup - freeing up resources that you can on your own closing open connections readers writers etc  If you don t override it  the system does what it has to   on the other hand  finish   just lets the system know that the programmer wants the current Activity to be finished  And hence  it calls up onDestroy   after that   Something to note   it isn t necessary that only a call to finish   triggers a call to onDestroy    No  As we know  the android system is free to kill activities if it feels that there are resources needed by the current Activity that are needed to be freed

User · Answer

Finish   method will destroy the current activity  You can use this method in cases when you dont want this activity to load again and again when the user presses back button  Basically it clears the activity from the current stack

User · Answer

Various answers and notes are claiming that finish   can skip onPause   and onStop   and directly execute onDestroy     To be fair  the Android documentation on this  http   developer android com reference android app Activity html  notes  Activity is finishing or being destroyed by the system  which is pretty ambiguous but might suggest that finish   can jump to onDestroy       The JavaDoc on finish   is similarly disappointing  http   developer android com reference android app Activity html finish    and does not actually note what method s  are called in response to finish     So I wrote this mini-app below which logs each state upon entry   It includes a button which calls finish   -- so you can see the logs of which methods get fired   This experiment would suggested that finish   does indeed also call onPause   and onStop     Here is the output I get   2170-2170   D LIFECYCLE DEMO  INSIDE  onCreate 2170-2170   D LIFECYCLE DEMO  INSIDE  onStart 2170-2170   D LIFECYCLE DEMO  INSIDE  onResume 2170-2170   D LIFECYCLE DEMO  User just clicked button to initiate finish    2170-2170   D LIFECYCLE DEMO  INSIDE  onPause 2170-2170   D LIFECYCLE DEMO  INSIDE  onStop  2170-2170   D LIFECYCLE DEMO  INSIDE  onDestroy  package com mvvg apps lifecycle   import android app Activity  import android os Bundle  import android util Log  import android view View  import android view View OnClickListener  import android widget Button  import android widget LinearLayout  import android widget Toast   public class AndroidLifecycle extends Activity        private static final String TAG    LIFECYCLE DEMO         Override     protected void onCreate Bundle savedInstanceState            super onCreate savedInstanceState           Log d TAG   INSIDE  onCreate            setContentView R layout activity main           LinearLayout layout    LinearLayout  findViewById R id myId           Button button   new Button this           button setOnClickListener new OnClickListener                   Override             public void onClick View view                    Toast makeText AndroidLifecycle this   Initiating finish                             Toast LENGTH SHORT  show                    Log d TAG   User just clicked button to initiate finish                      finish                                        layout addView button               Override     protected void onStart             super onStart            Log d TAG   INSIDE  onStart                Override     protected void onStop             super onStop            Log d TAG   INSIDE  onStop                Override     protected void onDestroy             super onDestroy            Log d TAG   INSIDE  onDestroy                Override     protected void onPause             super onPause            Log d TAG   INSIDE  onPause                Override     protected void onResume             super onResume            Log d TAG   INSIDE  onResume

User · Answer

My study shows that finish   method actually places some destruction operations in the queue  but the Activity is not destroyed immediately  The destruction is scheduled though   For example  if you place finish   in onActivityResult   callback  while onResume   has yet to run  then first onResume   will be executed  and only after that onStop   and onDestroy   are called   NOTE  onDestroy   may not be called at all  as stated on the documentation

User · Answer

calling finish in onCreate   will not call onDestroy   directly as  prakash said  The finish   operation will not even begin until you return control to Android   Calling finish   in onCreate    onCreate   -  onStart   -  onResume    If user exit the app will call -  onPause   -  onStop   -  onDestroy    Calling finish   in onStart     onCreate   -  onStart   -  onStop   -  onDestroy    Calling finish   in onResume    onCreate   -  onStart   -  onResume   -  onPause   -  onStop   -  onDestroy     For further reference check look at this oncreate continuous after finish  amp  about finish

User · Answer

user3282164 According to the Activity life-cycle it should go through onPause   -  onStop   -  onDestroy   upon calling finish     The diagram does not show any straight path from  Activity Running  to  onDestroy    caused by the system   onStop   doc says  Note that this method may never be called  in low memory situations where the system does not have enough memory to keep your activity s process running after its onPause   method is called

User · Answer

Also notice if you call finish   after an intent you can t go back to the previous activity with the  back  button  startActivity intent   finish

User · Answer

finish    just sends back to the previous activity in android  or may be you can say that it is going one step back in application

User · Answer

It seems that the only correct answer here so far has been given by romnex   onDestroy   may not be called at all   Even though in practice  in almost all cases it will  there is no guarantee  The documentation on finish   only promises that the result of the activity is propagated back to the caller  but nothing more  Moreover  the lifecycle documentation clarifies that the activity is killable by the OS as soon as onStop   finishes  or even earlier on older devices   which  even though unlikely and therefore rare to observe in a simple test  might mean that the activity might be killed while or even before onDestroy   is executed   So if you want to make sure some work is done when you call finish    you cannot put it in onDestroy    but will need to do in the same place where you call finish    right before actually calling it

User · Answer

My 2 cents on  K Anas answer  I performed a simple test on finish   method  Listed important callback methods in activity life cycle   Calling finish   in onCreate    onCreate   -  onDestroy   Calling finish   in onStart     onCreate   -  onStart   -  onStop   -  onDestroy   Calling finish   in onResume    onCreate   -  onStart   -  onResume   -  onPause   -  onStop   -  onDestroy     What I mean to say is that counterparts of the methods along with any methods in between are called when finish   is executed    eg     onCreate   counter part is onDestroy    onStart   counter part is onStop    onPause   counter part is onResume

User · Answer

When calling finish   on an activity   the method onDestroy   is executed  This method can do things like    Dismiss any dialogs the activity was managing  Close any cursors the activity was managing  Close any open search dialog   Also  onDestroy   isn t a destructor  It doesn t actually destroy the object  It s just a method that s called based on a certain state  So your instance is still alive and very well  after the superclass s onDestroy   runs and returns Android keeps processes around in case the user wants to restart the app  this makes the startup phase faster  The process will not be doing anything and if memory needs to be reclaimed  the process will be killed

[android] What is Activity.finish() method doing exactly?

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