One of the most frequent question about Fragments is how Fragments communicate to each other? how we can build a factory mechanism for this communication in a proper way? OnResume() should be used for normal Activity's and onResumeFragments() when using the v4 compat library , Notice in this cycle diagram, maybe a little bit different when using V4 library, for example in V4 in addition to onResume we have onResumeFragment which is called in Activity each time Fragment is loaded, When onAttach is invoked on Fragment, before fallthrough next step onCreate, Activity is notified of attachment by invoking onAttachFragment on Activity, this operation is synchronous and Fragment onCreate is called after onAttachFragment has been invoked. onViewStateRestored ( State restored but not called upon restart! )Īctivity is going through its own lifecycle during the Fragment loading but some subtle communications is coordinated between Fragment and Activity in order to get informed about each step in Fragment creation there a brief explanation :.onActivit圜reated ( Activity created but not called upon restart! ).onAttach ( Fragment is attached to Activity ). Notice if you set setRetainInstance(true), this has a big impact on Fragment lifecycle, in this case fragment instance remain undestroyed when detached from Activity, it ’ s maybe useful in the case you don’t keep your instance after change in configuration and you don’t want to go not into the whole process of Fragment recreation Will be closely related to the the pattern of Activity lifecycle,at the same time they have their own lifecycle pattern, so the complexity comes when activity lifecycle is not well coupled with Fragment lifecycle and vice versa! As you can see in the following lifecycle diagram in which Fragment and activity lifecycle are compared, when a fragment instance is created the first method called is onInflate(), this is the place when we can retrieve some attributes values, but notice this method is now deprecated in API level 23, and maybe not available anymore in latest version, so should avoid to use it.Then immediately after onInflate() ,system attach the fragment to Activity and onAttach() will be invoked on Fragment, this process then followed by invoking onAttachFragment on Activity, then Fragment onCreate is called notice at this this stage Fragment View is not still created it will be created just after Fragment’s onCreate by calling onCreateView but still not fully exposed, the View creation is completed by invoking onViewCreated.ĭuring all this process on Fragment side, Activity on the other side is completing in parallel its lifecycle once Activity creation is done the next step for Fragment lifecycle is onActivit圜reated() which will be called to indicate Fragment Activity is created, notice onActivit圜reated() is only called in a start process not restart! if Fragment is already created and attached, when restarted onActivit圜reated() is not called and this is the root cause of many issues developers face when they setup thier initialization here and get surprized when upon a restart onActivit圜reated() is not called! the next step onViewStateResored() follows the same pattern and upon restart it ’ s not being called. The first thing you should know about Fragments is that they are not a standalone components, instead that they are hosted by an Activity, so their lifecycle performDestroy is called first if f.Fragments are the most lovely pieces of app used by Android Developers and a deep understanding of it help developers to avoid many pitfalls & unexpected behavior in process Take a look at Fragment class (line 1564), performDestroy is called first if f.mRetaining is false : if (DEBUG) Log.v(TAG, "movefrom CREATED: " + f) Ref: android-fragment-lifecycle, onDestroy, onDetach (Called when the fragment is no longer attached to its activity) OnDetach() : onDetach() called after onDestroy(), to notify that the fragment has been disassociated from its hosting activity. (Called when the fragment is no longer in use, after onStop and before onDetach()) OnDestroy() : onDestroy() called to do final clean up of the fragment’s state but Not guaranteed to be called by the Android platform.
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