Concat Adapters Droidcon APAC 2020

ConcatAdapter is a new api exposed in recycler view which enables us to sequentially combine multiple adapters.
Learn how to better encapsulate your adapters having different data sources.
Different use cases where concat adapter can be used in an easy & elegant way.

Transcript

1. Concat adapters: Easy & elegant way of combining adapters Abhishesh Srivastava https://twitter.com/abhishesh_sri https://github.com/abhishesh-srivastava
2. Sprint 1
3. Too simple. Isn’t it? class WowAdapter : RecyclerView.Adapter<RecyclerView.ViewHolder>() { … override fun getItemViewType(position: Int): Int { if (position == 0) { return VIEW_TYPE_HEADER_1 } return VIEW_TYPE_DATA_SOURCE_1 } … }
4. Sprint 2
5. I know my game very well!!! class MessAdapter : RecyclerView.Adapter<RecyclerView.ViewHolder>() { … override fun getItemViewType(position: Int): Int { if (position == 0) { return VIEW_TYPE_HEADER_1 } else if (position < dataSource1.size) { return VIEW_TYPE_DATA_SOURCE_1 } else if (position == dataSource1.size + 1) { return VIEW_TYPE_HEADER_2 } else { return VIEW_TYPE_DATA_SOURCE_2; } } … }
6. Sprint 3
7. Hold on hold on. I will figure something out class HellAdapter : RecyclerView.Adapter<RecyclerView.ViewHolder>() { … override fun getItemViewType(position: Int): Int { if (position == 0) { return VIEW_TYPE_HEADER_1 } else if (position < dataSource1.size) { return VIEW_TYPE_DATA_SOURCE_1 } else if (position == dataSource1.size + 1) { return VIEW_TYPE_HEADER_3 } else if (position < (dataSource1.size + dataSource3.size)) { return VIEW_TYPE_DATA_SOURCE_3 } else if (position == dataSource1.size + dataSource2.size) { return VIEW_TYPE_HEADER_2 } else { return VIEW_TYPE_DATA_SOURCE_2 } } … }
8. Refactor? class HellAdapter : RecyclerView.Adapter<RecyclerView.ViewHolder>() { … override fun getItemViewType(position: Int): Int { if (position == 0) { return VIEW_TYPE_HEADER_1 } else if (position < dataSource1.size) { return VIEW_TYPE_DATA_SOURCE_1 } else if (position == dataSource1.size + 1) { return VIEW_TYPE_HEADER_3 } else if (position < (dataSource1.size + dataSource3.size)) { return VIEW_TYPE_DATA_SOURCE_3 } else if (position == dataSource1.size + dataSource2.size) { return VIEW_TYPE_HEADER_2 } else { return VIEW_TYPE_DATA_SOURCE_2 } } … }
9. Problems • Endless If-Else If statement
10. Problems • Endless If-Else If statement • Maintenance
11. Problems • Endless If-Else If statement • Maintenance • Breaks Single Responsibility
12. Problems • Endless If-Else If statement • Maintenance • Breaks Single Responsibility • Cannot reuse
13. Solution Let’s have our AHA(Android Has an Abstraction) moment Concat adapters to the rescue Alternatives : Epoxy, Bento
14. Concat adapters • Added in recyclerview 1.2.0-alpha02 as MergeAdapter • Renamed to ConcatAdapter in 1.2.0-alpha04 • Presents content of multiple adapters in sequence
15. Adapter 1 Adapter 3 Adapter 2
16. Why? • Encapsulate adapters rathers than merging data source and adapter into one. • Less error-prone. • Code reusability • Reduced code complexity
17. Show us some code
18. Concat adapter way!! val adapter1: AwesomeAdapter = ... val adapter2: GreatAdapter = ... val adapter3: SingleResponsibilityAdapter = ... val concatenated: ConcatAdapter = ConcatAdapter(adapter1, adapter2, adapter3); recyclerView.setAdapter(concatenated);
19. API public boolean addAdapter(int index, @NonNull Adapter<? extends ViewHolder> adapter) { } public boolean removeAdapter(@NonNull Adapter<? extends ViewHolder> adapter) { }
20. API public boolean addAdapter(int index, @NonNull Adapter<? extends ViewHolder> adapter) { } Adds an adapter at specified index. Note: It’s not the recyclerview adapter
21. API public boolean removeAdapter(@NonNull Adapter<? extends ViewHolder> adapter) { } Removes an adapters from adapter list
22. API public static final Config DEFAULT = new Config(true, NO_STABLE_IDS); public ConcatAdapter(@NonNull List<? extends Adapter<? extends ViewHolder>> adapters) { this(Config.DEFAULT, adapters); } public ConcatAdapter( @NonNull Config config, @NonNull List<? extends Adapter<? extends ViewHolder>> adapters) { }
23. ConcatAdapter.Config Config(boolean isolateViewTypes, @NonNull StableIdMode stableIdMode) { }
24. ConcatAdapter.Config Config(boolean isolateViewTypes, @NonNull StableIdMode stableIdMode) { } Local/global view pool
25. ConcatAdapter.Config Config(boolean isolateViewTypes, @NonNull StableIdMode stableIdMode) { } NO_STABLE_IDS: Default. Individual adapters stable id would be ignored. ISOLATED_STABLE_IDS: Individual adapters to have stable ids. SHARED_STABLE_IDS: Child adapters should never report the same stable id.
26. notifyDataSetChanged() public abstract static class Adapter<VH extends ViewHolder> { ... public final void notifyDataSetChanged() { mObservable.notifyChanged(); } public abstract static class AdapterDataObserver { ... @Override public void onChanged(@NonNull NestedAdapterWrapper wrapper) { mConcatAdapter.notifyDataSetChanged(); calculateAndUpdateStateRestorationPolicy(); } … }
27. Q&A
28. Thank you!