RecyclerView: In & Out - Speaker Deck

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RecyclerView: In & Out

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Why RecyclerView?!

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Item Decoration Adapter Recycled View Pool Layout Manager RecyclerView Item Animator Child Helper Adapter Helper Recycler

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Pro RecyclerView RecyclerView Animations Worth watching videos

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Components: ● RecyclerView ● Adapter ● LayoutManager ● ItemDecoration ● ItemAnimator ● ItemTouchHelper ● SnapHelper ● DiffUtil

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Components: ● RecyclerView creating, binding and recycling our views ● Adapter ● LayoutManager ● ItemDecoration ● ItemAnimator ● ItemTouchHelper ● SnapHelper ● DiffUtil

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Components: ● RecyclerView creating, binding and recycling our views ● Adapter provides data (RecyclerView.Adapter) ● LayoutManager ● ItemDecoration ● ItemAnimator ● ItemTouchHelper ● SnapHelper ● DiffUtil

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class MyAdapter extends RecyclerView.Adapter { public ItemHolder onCreateViewHolder(ViewGroup parent, int viewType) { …... } public void onBindViewHolder(ItemHolder holder, int position) { …... } }

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Adapter vs Layout Positions int getChildLayoutPosition(View child) {...} int getChildAdapterPosition(View child) {...}

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ItemDecoration class ItemDecoration{ public void onDraw(Canvas c, RecyclerView parent, State state) {...} public void onDrawOver(Canvas c, RecyclerView parent, State state) {...} public void getItemOffsets(Rect outRect, View view, RecyclerView parent, State state) {...} }

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Space evenly android:clipToPadding="false"

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What if we want to customize the padding override fun getItemOffsets(outRect: Rect, view: View, parent: RecyclerView, state: RecyclerView.State) { //access view holder val viewHolder = parent.getChildViewHolder(view) val params = view.layoutParams as GridLayoutManager.LayoutParams val layoutManager = parent.layoutManager as GridLayoutManager //how much space view is occupied val spanSize = params.spanSize //number of spans in the grid val totalSpanSize = layoutManager.spanCount //position depends on the RTL val position = params.spanIndex ... }

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What if we want to customize the padding override fun getItemOffsets(outRect: Rect, view: View, parent: RecyclerView, state: RecyclerView.State) //access view holder val viewHolder = parent.getChildViewHolder(view) val params = view.layoutParams as GridLayoutManager.LayoutParams val layoutManager = parent.layoutManager as GridLayoutManager //how much space view is occupied val spanSize = params.spanSize //number of spans in the grid val totalSpanSize = layoutManager.spanCount //position depends on the RTL val position = params.spanIndex … }

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What if we want to customize the padding override fun getItemOffsets(outRect: Rect, view: View, parent: RecyclerView, state: RecyclerView.State) { … if ((spanSize + position) == total) { outRect.right = padding; } else if (position == 0) { outRect.left = padding; } else { outRect.left = padding; outRect.right = padding; } }

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Is it right?!! Brrrr…...

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What if we want to customize the padding override fun getItemOffsets(outRect: Rect, view: View, parent: RecyclerView, state: RecyclerView.State) { val params = view.layoutParams as GridLayoutManager.LayoutParams val layoutManager = parent.layoutManager as GridLayoutManager val spanSize = params.spanSize val totalSpanSize = layoutManager.spanCount val position = params.spanIndex val n = (totalSpanSize / spanSize).toFloat() val percent = (position / spanSize).toFloat() val leftPadding = padding * ((n - percent) / n) val rightPadding = padding * ((percent + 1) / n) outRect.left = leftPadding.toInt() outRect.right = rightPadding.toInt() }

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What if we want to customize the padding Phew, did it!!

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Small question?

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Solution GridLayoutManager(сontext, spanCount) But how wisely we can control the span size of each item? layouManager.spanSizeLookup = GridLayoutManager.SpanSizeLookup() { override fun getSpanSize(position: Int): Int { return (...) } }

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override fun onDraw(c: Canvas, parent: RecyclerView, state: RecyclerView.State) { val childCount = parent.childCount val manager = parent.layoutManager for (i in 0..childCount - 1) { val child = parent.get(i) val right = manager.getDecoratedRight(child) val left = manager.getDecoratedLeft(child) + paddingLeft val height = divider.intrinsicHeight ?: 0 val top = manager.getDecoratedBottom(child) val bottom = top + height divider.setBounds(left, top, right, bottom) divider.draw(c) } }

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override fun onDraw(c: Canvas, parent: RecyclerView, state: RecyclerView.State) { val childCount = parent.childCount val manager = parent.layoutManager for (i in 0..childCount - 1) { val child = parent.get(i) val right = manager.getDecoratedRight(child) val left = manager.getDecoratedLeft(child) + paddingLeft val height = divider.intrinsicHeight val top = manager.getDecoratedBottom(child) val bottom = top + height divider.setBounds(left, top, right, bottom) divider.draw(c) } }

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Position override fun onDraw(c: Canvas, parent: RecyclerView, state: RecyclerView.State) { for (i in 0..childCount - 1) { val child = parent.get(i) parent.getChildAdapterPosition(child) } }

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Position override fun onDraw(c: Canvas, parent: RecyclerView, state: RecyclerView.State) { for (i in 0..childCount - 1) { val child = parent.get(i) parent.getChildAdapterPosition(child) } } NO_POSITION while animating

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Position override fun onDraw(c: Canvas, parent: RecyclerView, state: RecyclerView.State) { for (i in 0..childCount - 1) { val child = parent.get(i) parent.getChildLayoutPosition(child) } }

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Components: ● RecyclerView creating, binding and recycling our views ● Adapter provides data (RecyclerView.Adapter) ● LayoutManager layouting and positioning (Linear/GridLayout managers) ● ItemDecoration provides decoration for items (DividerItemDecoration) ● ItemAnimator defines the animations (DefaultItemAnimator) ● ItemTouchHelper ● SnapHelper ● DiffUtil

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DefaultItemAnimator object :LinearLayoutManager(context) { override fun supportsPredictiveItemAnimations() return true }

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val touchCallback = SwipeTouchCallback() val itemTouchHelper = ItemTouchHelper(touchCallback) itemTouchHelper.attachToRecyclerView(list)

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class SwipeTouchCallback(private val callback: ItemTouchHelperAdapter) : ItemTouchHelper.SimpleCallback(0, ItemTouchHelper.START or ItemTouchHelper.END) { override fun onMove(recyclerView: RecyclerView, viewHolder: RecyclerView.ViewHolder, target: RecyclerView.ViewHolder): Boolean { callback.onItemMove(viewHolder.adapterPosition, target.adapterPosition) return true } override fun onSwiped(viewHolder: RecyclerView.ViewHolder, direction: Int) { callback.onItemDismiss(viewHolder.adapterPosition) } }

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class SwipeTouchCallback(private val callback: ItemTouchHelperAdapter) : ItemTouchHelper.SimpleCallback(0, 0) { override fun getSwipeDirs(recyclerView: RecyclerView, viewHolder: RecyclerView.ViewHolder): Int {...} }

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Items with RecyclerView and horizontal LinearLayoutManager like CAROUSEL val snapHelper = LinearSnapHelper() snapHelper.attachToRecyclerView(this) LinearSnapHelper - Center snapping GravitySnapHelper(...): Gravity.START Gravity.END Gravity.BOTTOM Gravity.TOP rubensousa.github.io/2016/08/recyclerviewsnap

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Revision 25.1.0 LinearLayoutManager. setInitialPrefetchItemCount(N) https://medium.com/google-developers/recyclerview-prefetch-c2f269075710

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notifyItemChanged(…) notifyItemRangeChanged(…) notifyItemAdded(…) notifyItemRangeAdded(…) notifyItemRemoved(…) notifyItemRangeRemoved(…) notifyItemMoved(…) … and notifyChanged();

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val diffResult = DiffUtil.calculateDiff( MyDiffCallback(bricks, newList)) //change adapter adapter.swapData(newList) //dispatch changes diffResult.dispatchUpdatesTo(adapter)

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class MyDiffCallback(private var newBricks: List, private var oldBricks: List) : DiffUtil.Callback() { override fun getOldListSize(): Int { return oldBricks.size } override fun getNewListSize(): Int { return newBricks.size } override fun areItemsTheSame(oldItemPosition: Int, newItemPosition: Int): Boolean { return oldBricks[oldItemPosition].id === newBricks[newItemPosition].id } override fun areContentsTheSame(oldItemPosition: Int, newItemPosition: Int): Boolean { return oldBricks[oldItemPosition].equals(newBricks[newItemPosition]) } }

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class MyDiffCallback(private var newBricks: List, private var oldBricks: List) : DiffUtil.Callback() { … override fun getChangePayload(oldItemPosition: Int, newItemPosition: Int): Any { return super.getChangePayload(oldItemPosition, newItemPosition) } } notifyItemChanged(int position, Object payload) notifyItemRangeChanged(int positionStart, int itemCount, Object payload)

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Холливар Multiple View Types

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Naïve way public class ViewTypes { private static final int VIEW_TYPE_NORMAL = 0; private static final int VIEW_TYPE_SUBHEADER = 1; private static final int VIEW_TYPE_SEPARATOR = 2; private static final int VIEW_TYPE_HEADER = 3; }

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Naïve way @Override public int getItemViewType(int position) { NavigationMenuItem item = mItems.get(position); if (item instanceof NavigationMenuSeparatorItem) { return VIEW_TYPE_SEPARATOR; } else if (item instanceof NavigationMenuHeaderItem) { return VIEW_TYPE_HEADER; } else if (item instanceof NavigationMenuTextItem) { NavigationMenuTextItem textItem = (NavigationMenuTextItem) item; if (textItem.getMenuItem().hasSubMenu()) { return VIEW_TYPE_SUBHEADER; } else { return VIEW_TYPE_NORMAL; } } throw new RuntimeException("Unknown item type."); }

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Naïve way - item creation @Override public ViewHolder onCreateViewHolder(ViewGroup parent, int viewType) { switch (viewType) { case VIEW_TYPE_NORMAL: return new NormalViewHolder(mLayoutInflater, parent, mOnClickListener); case VIEW_TYPE_SUBHEADER: return new SubheaderViewHolder(mLayoutInflater, parent); case VIEW_TYPE_SEPARATOR: return new SeparatorViewHolder(mLayoutInflater, parent); case VIEW_TYPE_HEADER: return new HeaderViewHolder(mHeaderLayout); } return null; }

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Binding @Override public void onBindViewHolder(ViewHolder holder, int position) { switch (getItemViewType(position)) { case VIEW_TYPE_NORMAL: { NavigationMenuItemView itemView = (NavigationMenuItemView) holder.itemView; ... break; } case VIEW_TYPE_SUBHEADER: { TextView subHeader = (TextView) holder.itemView; NavigationMenuTextItem item = (NavigationMenuTextItem) mItems.get(position); ... break; } case VIEW_TYPE_SEPARATOR: case VIEW_TYPE_HEADER: ... } }

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After implementation

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Solutions - Favor composition over inheritance interface AdapterDelegate { fun isForViewType(items: T, position: Int): Boolean fun onCreateViewHolder(parent: ViewGroup): RecyclerView.ViewHolder fun onBindViewHolder(items: T, position: Int, holder: RecyclerView.ViewHolder) }

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Solutions - Favor composition over inheritance class NewsTipAdapter : RecyclerView.Adapter{ var delegates: MutableList() init{ delegates.add(NewsTeaserAdapterDelegate()) // Assigns internally ViewType integer delegates.add(PetFoodTipAdapterDelegate()) } .... }

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Solutions - Favor composition over inheritance class NewsTipAdapter : RecyclerView.Adapter() { ... override fun onBindViewHolder(holder: VH, position: Int) { delegates.forEach { if (it.isForViewType(items, position)) { // Main concern here it.onBindViewHolder(items, position, holder) return@forEach } } } }

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Composition class CatAdapterDelegate() : AdapterDelegate>() { protected fun isForViewType(items: List, position: Int): Boolean { return items[position] is Cat } } http://hannesdorfmann.com/android/adapter-delegates

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Epoxy https://github.com/airbnb/epoxy https://medium.com/airbnb-engineering/epoxy-airbnbs-view-architecture-on-android-c3e1af150394

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Epoxy class HeaderModel : EpoxyModel() { var city: City fun bind(headerView: HeaderView) { headerView.setImage(city.getImage()) headerView.setTitle(city.getName()) headerView.setDescription(city.getDescription()) } val defaultLayout: Int @LayoutRes get() = R.layout.model_header_view }

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Visitor interface ViewVisitor { fun type(typeFactory: TypeFactory): Int }

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Factory interface TypeFactoryImpl : TypeFactory { fun type(category: CategoryVisitor): Int fun type(categoryMovie: OverviewCategoryMovieVisitor): Int fun type(space: OverviewSpaceVisitor): Int fun type(movie: MoviesMovieVisitor): Int }

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interface TypeFactory { fun holder(type: Int, view: View): AdapterViewHolder<*> } ... class TypeFactoryImpl : TypeFactory { override fun type(category: CategoryVisitor) = R.layout.li_vod_category override fun holder(type: Int, view: View): AdapterViewHolder<*> { return when (type) { R.layout.li_vod_category -> CategoryHolder(view) R.layout.li_vod_overview_category_movie -> OverviewCategoryMovieHolder(view) R.layout.v_li_space_horizontal -> OverviewSpaceHolder(view) R.layout.li_vod_movie -> MoviesMovieHolder(view) else -> throw RuntimeException("Illegal view type") } } }

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abstract class AdapterViewHolder(view: View) : RecyclerView.ViewHolder(view) { abstract fun bind(item: T, position: Int) abstract fun recycled(holder: AdapterViewHolder<*>) } class VodMoviesMovieVisitor(val movie: MovieDisplayObject) : VodViewVisitor { override fun type(typeFactory: VodTypeFactory): Int = typeFactory.type(this) } class VodMoviesMovieHolder(view: View) : SimpleAdapterViewHolder(view) { ... override fun bind(item: VodMoviesMovieVisitor, position: Int) { .. } }

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Read&watch ● https://www.youtube.com/watch?v=imsr8NrIAMs ● https://realm.io/news/360andev-yigit-boyar-pro-recyclerview-android-ui-java/ ● http://frogermcs.github.io/recyclerview-animations-androiddevsummit-write-up/ ● http://hannesdorfmann.com/android/adapter-delegates ● https://medium.com/@nullthemall/diffutil-is-a-must-797502bc1149#.28n56v7zr ● https://medium.com/@dpreussler/writing-better-adapters-1b09758407d2#.9vzaoxz5e ● http://www.devexchanges.info/2016/09/android-tip-recyclerview-snapping-with.html ● https://guides.codepath.com/android/using-the-recyclerview ● https://medium.com/@ipaulpro/drag-and-swipe-with-recyclerview-b9456d2b1aaf

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Certificate of achievement awarded to Attendees for outstanding knowledge on RecyclerView

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Feedback https://goo.gl/2upLcm