Fragment view state retention: A dirty solution

This is the last part of this 6 part series about Fragment Oriented Architecture in Android applications. In the previous post I talked about managing sessions in fragment oriented application. In this post I am going to talk about retaining view hierarchy of a Fragment after removing it from container and then coming back to it by popping the backstack.

(Sample application's source code and README)

When a fragment gets replaced by another fragment and the transaction is added to back stack, the expectation after a popBackStack() is to return to the previous fragment with its UI state intact. Activity backstack takes care of this expectation quite cleanly until a low-memory situation occurs. But in case of fragments, this isn't the default behaviour. In a vanilla implementation, the replaced fragment's view-hierarchy would get recreated upon returning back to it. Reason is that during a replace operation, all the destructive life-cycle methods get called till onDestroyView(), which wipes out the view-hierarcy. Upon returning back, all the constructive lifecycle methods right from onCreateView() get called, thus, recreating the view-hierarchy totally afresh. Reason for this flow is to keep 'Fragments' memory friendly. Without the view-hierarchy, a fragment is just a java object with a bunch of instance variables.

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Session Management

This is the fifth part of a 6 posts series on Fragment oriented application architecture. In the previous post I talked about efficiently handling back button press inside fragment. In this part I am going to talk about session management in Fragment oriented application, by explaining integration of Facebook SDK.

(Sample application's source code and README)

In a fragment oriented application, we can conveniently manage all session related code in the activity and all its fragments would utilise it. Facebook SDK is quite in sync with this approach. Implementation of Facebook session is closely bound to an activity. And then this session is accessible throughout the application. As has been discussed before, if an application requires to sign in from different portions of it, it will be way more convenient to have those portions as parts of the same activity. So that the authentication code need not be duplicated.

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Handling back button press Inside Fragments

This is the fourth part of a 6 posts series on Fragment oriented application architecture. In the previous post I talked about Inter-Fragment Communication. In this part I am going discuss about elegantly handling back button press inside fragments in a fragment oriented application.

(Sample application's source code and README)

Android devices have a hardware back button which normally serves the purpose of going back through the screens/actions stack. Callback to a back button press event is received in the foreground Activity (onBackPressed() event callback) which can be overridden and handled.

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Inter-Fragment Communication

This is the third part of a 6 posts series on Fragment oriented application architecture. In the previous post I talked about Transaction BackStack and its management. In this part I am going to talk about Inter-Fragment Communication. It's a general concept, not deeply linked to the context of this series.

(Sample application's source code and README)

It's a communication pattern over which fragments should talk to each other. Ideally, a fragment should never keep a reference of another fragment or even, in best case, of the specific parent activity. So, how would two fragments communicate? Consider the following scene.

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Transaction BackStack and its management

This is second part of a 6 posts series. In the first post I talked around basics of fragment oriented architecture. From this post onwards, I'll be talking about it's implementation details.

(Sample application's source code and README)

In this part I am going to talk about Transaction Backstack and few related methods that can be used frequently.
Transaction BackStack has often been misinterpreted as backstack of fragments. FragmentManager inside an activity deals with fragment-transactions rather than with fragments. An entry into this backstack is a 'fragment-transaction' which can be composed of one or more operations involving fragment(s). Reverting this would revert back all these operations together.

FragmentTransaction ft = getFragmentManager().beginTransaction();
ft.add(restId, fragmentA);
ft.replace(fragmentB);
ft.commit();

Above, is a single transaction clubbing multiple operations.

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