Pro RecyclerView

Pro RecyclerView talk at 360andev / Denver / 2016

1. Pro RecyclerView Yiğit Boyar / Google
2. Define: Pro • Know the past and today • Use it properly & efficiently • (a.k.a best practices)
3. Part I Know The Past and Today
4. ListView • Repeated & Consistent Content
5. ListView • or sometimes, not so consistent • A lot of data, not enough memory
6. ListView • Smoke and mirrors! • If it looks right, it is right • Only create & layout the views user can see • Lay out more as needed, re-use!
7. Complexity Overdraft • A lot of long tail, one - off features • Undefined behavior when APIs are mixed • Undefined behavior = undefined API
8. Duplicate Features • Focused View vs Selected Item • Item Click Listener vs View Click Listener • setItemsCanFocus • why not?
9. Animations
10. ¯\_(ϑ)_/¯
11. More Complex Layouts • GridView • Horizontal List View • StaggeredGridView
12. Reboot • Elevates best practices • ViewHolder • De-couple via well defined components • Recycler • Do less • Use framework focus • Smart adapters
13. RecyclerView Components Layout Manager Adapter Item Animator I position the views I provide the views I animate the views Recycler View
14. Part II Best Practices
15. View::requestLayout
16. View::requestLayout requestLayout ViewGroup ViewGroup View ViewGroup view ViewGroup View ViewGroup View
17. View::requestLayout ViewGroup ViewGroup View ViewGroup view ViewGroup View ViewGroup View nextFrame measure
18. View::requestLayout ViewGroup ViewGroup View ViewGroup view ViewGroup View ViewGroup View layout
19. View::requestLayout onBindViewHolder(ViewHolder vh, int position) { .... imageLoader.loadImage(vh.image, user.profileUrl, R.drawable.placeHolder); }
20. imageView.setImageBitmap(bitmap)
21. imageView.setImageBitmap(bitmap) imageView.requestLayout();
22. imageView.setImageBitmap(bitmap) imageView.requestLayout(); itemView.requestLayout();
23. imageView.setImageBitmap(bitmap) imageView.requestLayout(); itemView.requestLayout(); recyclerView.requestLayout(); unless setHasFixedSize == true
24. ImageView.java Since 2011 void setImageDrawable(Drawable drawable){ if (mDrawable != drawable) { int oldWidth = mDrawableWidth; int oldHeight = mDrawableHeight; updateDrawable(drawable); if (oldWidth != mDrawableWidth || oldHeight != mDrawableHeight) { requestLayout(); } invalidate(); } }
25. TextView.java ¯\_(ϑ)_/¯
26. How Do I Know?
27. RecyclerView.java
28. Resizing Items
29. imageLoader.load( viewHolder.imageView); cache miss
30. desired
31. reality: bad item height Clock in the wrong column
32. AspectRatioImageView.java private float mAspectRatio; @Override protected void onMeasure(int wSpec, int hSpec) { int width = MeasureSpec.getSize(wSpec); int height = (int) (width * mAspectRatio); setMeasuredDimension(width, height); }
33. Bad API vs Good API {
 "user" : {
 "name" : "Michael",
 }
 } "photoUrl" : "https://..."

34. Bad API vs Good API {
 "user" : {
 "name" : "Michael",
 }
 } "photoUrl" : {
 "width" : 300,
 "height" : 500,
 "url" : "https://...",
 "palette" : {}
 }

35. DataBinding void onBindViewHolder(ViewHolder vh, int pos) { vh.binding.setItem(items.get(pos)); vh.binding.executePendingBindings(); }
36. Data Updates
37. updated list arrives void onFetched(List<News> news) { myAdapter.setNews(news); myAdapter.notifyDataSetChanged(); }
39. onBind onBind onBind onBind onBind create new VH
40. long getItemId(int position) { news.get(position).getId(); }
41. onBind unnecessary onBind, measure, layout
42. SortedList SortedList<Item> mySortedList = new SortedList<Item>(Item.class, new SortedListAdapterCallback<Item>(myAdapter) { @Override public int compare(Item item1, Item item2) { return item1.id - item2.id; } @Override public boolean areItemsTheSame(Item item1, Item item2) { return item1.id == item2.id; } @Override public boolean areContentsTheSame(Item oldItem, Item newItem) { return oldItem.text.equals(newItem.text); } });
43. SortedList void onFetched(List<News> newsList) { mySortedList.addAll(newsList); }
44. Sort By Votes
45. SortedList SortedList<Item> mySortedList = new SortedList<Item>(Item.class, new SortedListAdapterCallback<Item>(myAdapter) { @Override public int compare(Item item1, Item item2) { return item1.id - item2.id; } … }); update compare method
46. SortedList SortedList<Item> mySortedList = new SortedList<Item>(Item.class, new SortedListAdapterCallback<Item>(myAdapter) { @Override public int compare(Item item1, Item item2) { return item2.votes - item1.votes; } … });
47. SortedList Internals Article Votes Sharks To Finals 10 add(“To Rx…”, 9) 7 > 9 ? Shake The Phone 8 San Francisco Dating 7 To Rx or Not To Rx 5 Do Not Sleep 3
48. SortedList Internals Article Votes Sharks To Finals 10 add(“To Rx…”, 9) 10 > 12 ? Shake The Phone 8 San Francisco Dating 7 To Rx or Not To Rx 5 Do Not Sleep 3
49. SortedList Internals Article Votes Sharks To Finals 10 add(“To Rx…”, 9) 8 > 9 ? Shake The Phone 8 San Francisco Dating 7 To Rx or Not To Rx 5 Do Not Sleep 3
50. SortedList Internals Article Votes Sharks To Finals 10 Shake The Phone 8 San Francisco Dating 7 To Rx or Not To Rx 5 Do Not Sleep 3 To Rx or Not To Rx 9
51. SortedList::updateItemAt Map<Integer, Item> items; // item id -> Item void insert(Item item) { Item existing = items.put(item.id, item); if (existing == null) { mySortedList.add(item); } else { int ind = mySortedList.indexOf(existing); mySortedList.updateItemAt(ind, item); } }
52. Introducing…
53. DiffUtil
54. DiffUtil DiffResult result = DiffUtil.calculateDiff(new MyCallback(oldList, newList)); myAdapter.setItems(newList); result.dispatchUpdatesTo(myAdapter);
55. DiffUtil.Callback class MyCallback extends DiffUtil.Callback { @Override public int getOldListSize() { return mOld.size(); } @Override public int getNewListSize() { return mNew.size(); } @Override public boolean areItemsTheSame(int oldItemPosition, int newItemPosition) { return mOld.get(oldItemPosition).id == mNew.get(newItemPosition).id; } @Override public boolean areContentsTheSame(int oldItemPosition, int newItemPosition){ return mOld.get(oldItemPosition).equals(mNew.get(newItemPosition)); } }
56. DiffUtil.Callback @Override @Nullable public Object getChangePayload(int oldItemPosition, int newItemPosition) { Item oldItem = mOldItems.get(oldItemPosition); Item newItem = mNewItems.get(newItemPosition); if (oldItem.votes != newItem.votes) { return VOTES; } return null; }
57. Adapter::onBindViewHolder @Override public void onBindViewHolder(RecyclerView.ViewHolder holder, int position,List<Object> payloads) { if (payloads.isEmpty()) { onBindViewHolder(holder, position); } else { if (payloads.contains(VOTES)) { holder.voteCount.setText("" + item.votes); } } }
58. DiffUtil Available in 24.2
59. Resource Management
60. ViewHolder Lifecycle onCreate onViewAttachedToWindow onViewDetachedFromWindow onRecycled onBindViewHolder the same item stop playing video start playing video
61. ViewHolder Lifecycle onCreate onViewAttachedToWindow onViewDetachedFromWindow onRecycled onBindViewHolder might be a different item release video resources acquire video resources
62. RecyclerView is Async
63. RecyclerView Update Cycle on frame handle pending changes
64. RecyclerView Update Cycle on frame handle pending changes scroll to position notify data change smooth scroll all structural changes postponed until next layout
65. RecyclerView::scrollToPosition recyclerView.scrollToPosition(15); int x = layoutManager.getFirstVisibleItemPosition(); x == 15 ?
66. RecyclerView::scrollToPosition recyclerView.scrollToPosition(15); int x = layoutManager.getFirstVisibleItemPosition(); x == 15 ?
67. RecyclerView::scrollToPosition onInit void onCreate(SavedInstanceState state) { .... mRecyclerView.scrollToPosition(selectedPosition); mRecyclerView.setAdapter(myAdapter); } will it work? ✓
68. RecyclerView::scrollToPosition onInit void onCreate(SavedInstanceState state) { .... mRecyclerView.scrollToPosition(selectedPosition); model.loadItems(items -> mRecyclerView.setAdapter( new ItemAdapter(items)); ); } will it work? ✓
69. RecyclerView::scrollToPosition onInit void onCreate(SavedInstanceState state) { .... mRecyclerView.scrollToPosition(selectedPosition); model.loadItems(items -> mRecyclerView.setAdapter( new ItemAdapter(items)); ); } will it work? ✓ No layout happens until both Adapter and LayoutManager are set.
70. ViewHolder ++
71. Sad ViewHolder class ViewHolder { TextView title; TextView body; ImageView icon; } void onBindViewHolder(ViewHolder vh, int pos) { Item item = items.get(pos); title.setText(item.getTitle()); body.setText(item.getBody()); imageLoader.loadImage(icon, item.IconUrl()); }
72. Happy ViewHolder class ViewHolder { ... public bindTo(Item item, ImageLoader imageLoader) { title.setText(item.getTitle()); body.setText(item.getBody()); imageLoader.loadImage(icon, item.IconUrl()); } } void onBindViewHolder(ViewHolder vh, int position) { vh.bindTo(items.get(position), mImageLoader); }
73. View Types
74. Adapter::getItemViewType @Override public int getItemViewType(int position) { User user = mItems.get(position); if (user.isPremium()) { return TYPE_PREMIUM; } return TYPE_BASIC; }
75. Adapter::onCreateViewHolder public RecyclerView.ViewHolder onCreateViewHolder(ViewGroup parent, int viewType) { View view; switch (viewType) { case TYPE_PREMIUM: view = mLayoutInflater.inflate(R.layout.premium, parent, false); break; case TYPE_BASIC: view = mLayoutInflater.inflate(R.layout.basic, parent, false); break; } return new UserViewHolder(view); }
76. Adapter::getItemViewType @Override public int getItemViewType(int position) { User user = mItems.get(position); if (user.isPremium()) { return TYPE_PREMIUM; } return TYPE_BASIC; }
77. Adapter::getItemViewType @Override public int getItemViewType(int position) { User user = mItems.get(position); if (user.isPremium()) { return R.layout.premium; } return R.layout.basic; }
78. Adapter::onCreateViewHolder public RecyclerView.ViewHolder onCreateViewHolder(ViewGroup parent, int viewType) { View view = mLayoutInflater.inflate(viewType, parent, false); return new UserViewHolder(view); } it is the R.layout id ;)
79. Click Listeners
80. Where Is My Click Listener ? https://commons.wikimedia.org/wiki/File:Trollface.png
81. There Is Your Click Listener http://stackoverflow.com/questions/24885223/why-doesnt-recyclerview-have-onitemclicklistener-and-how-recyclerview-is-dif
82. There Is Your Click Listener ItemClickListener prevents children clicks http://stackoverflow.com/questions/24885223/why-doesnt-recyclerview-have-onitemclicklistener-and-how-recyclerview-is-dif
83. ItemClickListener class MyAdapter { ItemClickListener itemClickListener; public onCreateViewHolder(...) { final ViewHolder vh = ....; myViewHolder.itemView.setOnClickListener({ int pos = vh.getAdapterPosition(); if (pos != NO_POSITION) { itemClickListener.onClick(items[pos]); } }); } } ItemClick NOT View.Click
84. Adapter Position vs Layout Position
85. Positions: Adapter vs Layout London İstanbul San Francisco New York Barcelona Paris AP LP 0 0 1 1 2 2 3 3 4 4 5 5 move(2,5);
86. Positions: Adapter vs Layout London İstanbul San Francisco New York Barcelona Paris move(2,5); AP LP 0 0 1 1 5 2 2 3 3 4 4 5
87. Positions: Adapter vs Layout London İstanbul New York Barcelona Paris San Francisco onLayout AP LP 0 0 1 1 2 2 3 3 4 4 5 5
88. Things That Makes Me Sad :(
89. MySuperSolidRecyclerView class MySuperSolidRecyclerView extends RecyclerView { public void onLayout() { try { super.onLayout(); } catch (Throwable t) { // ignore } } }
90. MySuperSolidRecyclerView class MySuperSolidRecyclerView extends RecyclerView { public void onLayout() { try { super.onLayout(); } catch (Throwable t) { // ignore } } } NO NO NO NO fix your crash! (or report a bug :) )
91. Old Habits Die Hard public void onBindViewHolder(ViewHolder vh, final int position) { vh.likeButton.setOnClickListener = new OnClickListener() { items[position].liked = true; notifyItemChanged(position); } }
92. Old Habits Die Hard public void onBindViewHolder(ViewHolder vh, final int position) { vh.likeButton.setOnClickListener = new OnClickListener() { items[position].liked = true; notifyItemChanged(position); } } NO vh.getAdapterPosition()
93. Old Habits Die Hard public void onBindViewHolder(ViewHolder vh, final int position) { vh.likeButton.setOnClickListener = new OnClickListener() { items[position].liked = true; notifyItemChanged(position); } } NO NO NO use onCreateVH
94. Create public void onCreateViewHolder(int type) { if (type == HEADER) { if (headerVH == null) { headerVH = new HeaderViewHolder(...); } return headerVH; } }
95. Create public void onCreateViewHolder(int type) { if (type == HEADER) { if (headerVH == null) { headerVH = new HeaderViewHolder(...); } return headerVH; } } NO NO NO NO
96. Create public void onCreateViewHolder(int type) { if (type == HEADER) { if (headerVH == null) { headerVH = new HeaderViewHolder(...); } return headerVH; } } NO NO NO NO
97. Fooling* The RecyclerView void refreshData() { new AsyncTask(...) { void doInBackground() { List<Item> items = webservice.fetch(); adapter.setData(items); adapter.notifyDataSetChanged(); } } }
98. Fooling* The RecyclerView void refreshData() { new AsyncTask(...) { void doInBackground() { List<Item> items = webservice.fetch(); adapter.setData(items); adapter.notifyDataSetChanged(); } } } NO NO NO
99. Fooling* The RecyclerView void refreshData() { new AsyncTask(...) { void doInBackground() { List<Item> items = webservice.fetch(); adapter.setData(items); } void onPostExecute() { adapter.notifyDataSetChanged(); } } }
100. Fooling* The RecyclerView void refreshData() { new AsyncTask(...) { void doInBackground() { List<Item> items = webservice.fetch(); adapter.setData(items); } void onPostExecute() { adapter.notifyDataSetChanged(); } } } NO NO NO
101. Fooling* The RecyclerView void refreshData() { new AsyncTask(...) { List<Item> doInBackground() { List<Item> items = webservice.fetch(); return items; } void onPostExecute(List<Item> items) { adapter.setData(items); adapter.notifyDataSetChanged(); } } }
102. Thank You!
103. Certificate of Achievement awarded to: 360|AnDev Attendee for outstanding knowledge on RecyclerView