Difference between onStart and onResume

Question

I can t get the meaning of onStart   transition state  The onResume   method is always called after onStart    Why can t it be the onResume   is invoked after onRestart   and onCreate   methods just excluding onStart    What is its purpose   Why can t we live without onStart    I still consider it as redundant  probably because don t understand its meaning completely

User · Answer

onResume   is called    after onStart   when the Activity comes to the foreground    From http   developer android com reference android app Activity html ActivityLifecycle

User · Answer

Hopefully a simple explanation   -  onStart   -  called when the activity becomes visible  but might not be in the foreground  e g  an AlertFragment is on top or any other possible use case    onResume   -  called when the activity is in the foreground  or the user can interact with the Activity

User · Answer

Reference to http   developer android com training basics activity-lifecycle starting html   onResume   Called just before the activity starts interacting with the user  At this point the activity is at the top of the activity stack  with user input going to it  Always followed by onPause     onPause   Called when the system is about to start resuming another activity  This method is typically used to commit unsaved changes to persistent data  stop animations and other things that may be consuming CPU  and so on  It should do whatever it does very quickly  because the next activity will not be resumed until it returns  Followed either by onResume   if the activity returns back to the front  or by onStop   if it becomes invisible to the user

User · Answer

Short answer   We can t live without onStart because that is the state when the activity becomes  visible  to the user  but the user cant  interact  with it yet may be cause it s overlapped with some other small dialog  This ability to interact with the user is the one that differentiates onStart and onResume  Think of it as a person behind a glass door  You can see the person but you can t interact  talk listen shake hands  with him  OnResume is like the door opener after which you can begin the interaction   Additionally onRestart   is the least understood one  We can ask the question as to why not directly go to onStart   or onResume   after onStop   instead of onRestart    It becomes easier to understand if we note that onRestart   is partially equivalent to onCreate   if the creation part is omitted  Basically both states lead to onStart    i e the Activity becomes visible   So both the states have to  prepare  the stuff to be displayed  OnCreate has the additional responsibility to  create   the stuff to be displayed  So their code structures might fit to something like   onCreate          createNecessaryObjects          prepareObjectsForDisplay        onRestart          prepareObjectsForDisplay         The entire confusion is caused since Google chose non-intuitive names instead of something as follows   onCreateAndPrepareToDisplay      instead of onCreate     onPrepareToDisplay               instead of onRestart     onVisible                        instead of onStart     onBeginInteraction               instead of onResume     onPauseInteraction               instead of onPause     onInvisible                      instead of onStop  onDestroy                        no change     The Activity Diagram might be interpreted as

User · Answer

Why can t it be the onResume   is invoked after onRestart   and onCreate   methods just excluding onStart    What is its purpose    OK  as my first answer was pretty long I won t extend it further so let s try this     public DriveToWorkActivity extends Activity     implements onReachedGroceryStoreListener      public GroceryStoreActivity extends Activity      PLEASE NOTE  I ve deliberately left out the calls to things like super onCreate      etc  This is pseudo-code so give me some artistic licence here      The methods for DriveToWorkActivity follow     protected void onCreate            openGarageDoor        unlockCarAndGetIn        closeCarDoorAndPutOnSeatBelt        putKeyInIgnition       protected void onStart         startEngine        changeRadioStation        switchOnLightsIfNeeded        switchOnWipersIfNeeded       protected void onResume         applyFootbrake        releaseHandbrake        putCarInGear        drive       protected void onPause         putCarInNeutral        applyHandbrake       protected void onStop         switchEveryThingOff        turnOffEngine        removeSeatBeltAndGetOutOfCar        lockCar       protected void onDestroy         enterOfficeBuilding       protected void onReachedGroceryStore            Intent i   new Intent ACTION GET GROCERIES        this  GroceryStoreActivity class      protected void onRestart         unlockCarAndGetIn        closeDoorAndPutOnSeatBelt        putKeyInIgnition        OK  so it s another long one  sorry folks   But here s my explanation     onResume   is when I start driving and onPause   is when I come to a temporary stop  So I drive then reach a red light so I pause   the light goes green and I resume  Another red light and I pause  then green so I resume  The onPause   - gt  onResume   - gt  onPause   - gt  onResume   loop is a tight one and occurs many times through my journey   The loop from being stopped back through a restart  preparing to carry on my journey  to starting again is perhaps less common  In one case  I spot the Grocery Store and the GroceryStoreActivity is started  forcing my DriveToWorkActivity to the point of onStop     When I return from the store  I go through onRestart   and onStart   then resume my journey   I could put the code that s in onStart   into both onCreate   and onRestart   and not bother to override onStart   at all but the more that needs to be done between onCreate   - gt  onResume   and onRestart   - gt  onResume    the more I m duplicating things   So  to requote once more        Why can t it be the onResume   is invoked after onRestart   and onCreate   methods just excluding onStart      If you don t override onStart   then this is effectively what happens  Although the onStart   method of Activity will be called implicitly  the effect in your code is effectively onCreate   - gt  onResume   or onRestart   - gt  onResume

User · Answer

Note that there are things that happen between the calls to onStart   and onResume    Namely  onNewIntent    which I ve painfully found out    If you are using the SINGLE TOP flag  and you send some data to your activity  using intent extras  you will be able to access it only in onNewIntent    which is called after onStart   and before onResume    So usually  you will take the new  maybe only modified  data from the extras and set it to some class members  or use setIntent   to set the new intent as the original activity intent and process the data in onResume

User · Answer

A particularly feisty example is when you decide to show a managed Dialog from an Activity using showDialog    If the user rotates the screen while the dialog is still open  we call this a  configuration change    then the main Activity will go through all the ending lifecycle calls up untill onDestroy    will be recreated  and go back up through the lifecycles  What you might not expect however  is that onCreateDialog   and onPrepareDialog    the methods that are called when you do showDialog   and now again automatically to recreate the dialog - automatically since it is a managed dialog  are called between onStart   and onResume    The pointe here is that the dialog does not cover the full screen and therefore leaves part of the main activity visible  It s a detail but it does matter

User · Answer

onStart   called when the activity is becoming visible to the user  onResume   called when the activity will start interacting with the user  You may want to do different things in this cases   See this link for reference

User · Answer

The book  Hello  Android  Introducing Google s Mobile Development Platform  gives a nice explanation of the life cycle of android apps  Luckily they have the particular chapter online as an excerpt  See the graphic on page 39 in http   media pragprog com titles eband3 concepts pdf  By the way  this book is highly recommendable for android beginners

User · Answer

onStart   means Activity entered into visible state and layout is created but can t interact with this activity layout   Resume   means now you can do interaction with activity layout

User · Answer

Not sure if this counts as an answer - but here is YouTube Video From Google s Course  Developing Android Apps with Kotlin  that explains the difference    On Start is called when the activity becomes visible On Pause is called when the activity loses focus  like a dialog pops up  On Resume is called when the activity gains focus  like when a dialog disappears

User · Answer

onStart      Called after onCreate Bundle   or after onRestart   followed by onResume    you can register a BroadcastReceiver in onStart   to monitor changes that impact your UI  You have to unregister it in onStop   Derived classes must call through to the super class s implementation of this method  If they do not  an exception will be thrown    onResume     Called after onRestoreInstanceState Bundle   onRestart    or         onPause   Begin animations  open exclusive-access devices  such as the camera    onStart   normally dispatch work to a background thread  whose return values are    START STICKY to automatically restart if killed  to keep it active  START REDELIVER INTENT for auto restart and retry if the service was killed before stopSelf      onResume   is called by the OS after the device goes to sleep or after an Alert or other partial-screen child activity leaves a portion of the previous window visible so a method is need to re-initialize fields  within a try structure with a catch of exceptions    Such a situation does not cause onStop   to be invoked when the child closes   onResume   is called without onStart   when the activity resumes from the background  For More details you can visits Android activity lifecycle gotcha And Activity Lifecycle

[android] Difference between onStart() and onResume()

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