The modern way to pass data between fragments

Pass data through Fragment Manager

With Android Jetpack components a lot of things are happening here and there. Nowadays most of the developers tend to use Single Activity architecture, with that communicating between fragments become more crucial.

There are multiple ways to communicate between fragments. For example, using Interfaces or a shared ViewModel. But, this is sometimes additional overhead. As an alternative setTargetFragment could be used but, this is also now deprecated.

So, let's look at the modern way.

The modern way

Beginning from Fragment release 1.3.0-alpha04 and onwards FragmentManager can be used to communicate between fragments. Now FragmentManager by default implements from FragmentResultOwner and override the methods to set and clear fragment results and fragment result listeners.

How it works

The FragmentManager holds fragment results and fragment result listeners in separate Maps with requestKey as a unique identifier. The fragment result listener which registered to the relevant requestKey get notified when the result is set or updated.

This way it helps to communicate between fragments in the same FragmentManager and also child to parent fragment or vice versa.

To pass data between fragments in the same fragment manager, the listener should be added to the destination fragment with requestKey in order to receive the result produces from another fragment with the same key.

Set listener to the fragment to receive the result

Now, the source fragment should produce the result on the same FragmentManager with the same requestKey as follows:

Produce fragment result, to pass data to the destination

That's it, the destination fragment will receive the result and execute listener callback once it's STARTED.

To pass data from child to parent fragment, should follow the same way by using childFragmentManager instead parentFragmentManager when set result listener to the parent fragment.

Set listener to the fragment to receive the result from child fragment

Now, same as the previous example, child fragment should produce the result with the same requestKey.

Produce fragment result from child fragment

Yes, all you need. The parent fragment will receive the result immediately. If communication requires to be done other way around (pass data from parent to child fragment), the result listener should be set to child fragment and result should be produced from parent fragment. Then don't forget to use childFragmentManager instead parentFragmentManager when producing the result from the parent fragment.

Points to keep in mind

• Only a single listener and result can be registered to the given key. If more than one listener is registered for the same key, it will be replaced for the latest one.
• If destination fragment in back stack, and calls setFragmentResult() from source fragment more than once for the same key, the system sends the most recent result to the destination fragment before the source fragment is popped off the back stack.
• If the result is set without having listener to receive it, the result is stored in the FragmentManager until the listener is set with the same key. When the listener is set and the fragment is STARTED, it will receive the result immediately.
• The result will be cleared from FragmentManager once the destination fragment receives it.

The example project can be seen here and more info here.

Hope you learn something useful. See you in the next one ✌️