In this Notes article, I roughly jotted down notes in English from the content of the English session video/podcast. This article is intended to be read as a reference while watching the video. I hope this article helps you even a little when you watch the actual video. (Please feel free to contact me if there are any errors or typos! m(__)m)

This article is based on Fragments: Past, Present, and Future (Android Dev Summit ‘19).

Fragment Past

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Android API 11

Fragments were really designed from the beginning to the kind of Micro Activities.

• First step to move things from fat Activities to smaller fragments

  • this also meant that Fragments inherited a lot of APIs that Activity had

    • ActionBar Menus

  • this also meant that there became a lot custom hooks

    • Things activity got received needed to be received on Fragments as well

      • onActivityResult

      • Permissions

      • Multi Window

      • Picture in Picture

Present

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• Restructuring the goal of Fragments

  • focused API surfaces

    • core, simple, predictable no-surprise apis

    • without breaking changes

      • deprecating old apis with new better APIs

• Providing testable APIs

  • Fragment testing artifact

    • Fragment Scenario

      • moveToState(), recreate()

      • launchFragmentInContainer

    • Working together with AndroidX team

• Instantiating Fragments

  • Recreation after config change

  • FragmentTransaction add / replace

  • FragmentScenario

  • FragmentFactory

    • Support constructor injection

    • No requirement for no arg constructor

• One container for Fragments

  • FragmentContainerView

    • Use it instead of FrameLayout

    • Replace the <fragment> tag

    • does use FragmentManager under the hood

      • Fix issue of replacing fragment later

    • Fix the Z-ordering animation issue

• System back

  • OnBackPressedDispatcher

    • Arch Components

• ViewModels

  • by viewModels()

  • by navGraphViewModels(R.id.main)

  • by activityViewModels()

• Lifecycle

  • ?

Future

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• Subject to change

• multiple back stack

  • single stack: existing legacy on Android

  • allow saving and restoring a whole stack of fragments without losing state

  • Bottom nav made easy

• returning results

  • how do I talk between fragments?

  • fragment API right now is not great

  • create a better API for startActivityForResult() and for passing a result to another Fragment

    • building and hopefully sharing in a few months

• lifecycle

  • fragment has two lifecycles

    • fragment itself

    • fragment’s view has totally different lifecycle

      • view may get destroyed, but fragment still exists

  • what if, these two lifecycles are the same?

    • bringing these things together, we can solve a lot of complexity. => maybe this kind of opt-in APIs will be available in FragmentActivity level.

Impressions / Summary / Key Takeaways

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• FragmentFactory and FragmentScenario make it easier to create and test Fragments.
  • Using Factory also enables constructor injection.
• Use FragmentContainerView (instead of FrameLayout) when embedding Fragments in a View.
  • FragmentManager is used internally.
• Google has many more Fragment APIs they want to improve in the future.
  • Enabling multiple back stacks (to make management during BottomNav switching easier).
  • Making passing values between Fragment-Fragment easier (API changes around FragmentActivity might come in a few months?).
  • What if the Fragment’s own lifecycle and ViewLifecycle could be unified…???

Fragment APIs seem likely to become even easier to use and more intuitive.

That’s all!