f:id:shaunkawano:20191025202341p:plain

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本記事は、Fragments: Past, Present, and Future (Android Dev Summit '19)の記事です。

Fragment Past

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

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 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

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.

所感・まとめ・個人的に印象に残ったことなど

FragmentFactory、FragmentScenarioを使うことでFragmentの生成やテストがしやすくなったよ
- Factoryを使うことでconstructor injectionも可能になったよ
FragmentをViewに内包する場合にはFragmentContainerViewを使う(FrameLayoutは使わない)
- 内部ではFragmentManagerが利用されている
Googleとしては、将来的にももっともっと良くしていきたいFragment APIが沢山ある
- 複数のバックスタックを可能にする(BottomNavの切替時とかの管理を簡単にしたい)
- Fragment-Fragment間の値の受け渡しとかをより簡単にできたら（FragmnetActivityあたりへのAPI変更が数ヶ月以内にあるかも？）
- Fragment自体のLifecycleとViewLifecycleを1つにできるとしたら...???