Android Recycler View Lifecycle diagrams and notes

The following images are captured from the presentation 'RecyclerView ins and outs- Google IO 2016'
By: Adam Powell and Yigit Boyar

Main Components

ViewHolder Life Cycle

1. While Layout Manager is calculating layout, it asks RecyclerView for View objects
   recyclerView.getViewForPosition(...)
2. RecylcerView checks the Cache for a hit
   cache.getViewForPosition(...)
3. If in Cache, return to RecyclerView
4. RecyclerView returns to LayoutManager

1. While Layout Manager is calculating layout, it asks RecyclerView for View objects
   recyclerView.getViewForPosition()
2. RecylcerView checks the Cache for a hit
   cache.getViewForPosition()
3. Cache does not have a view
4. RecyclerView asks adapter for View Type
   adapter.getViewType()
5. RecyclerView asks Pool for ViewHolder for type
   pool.getViewHolderByType()
6. Pool does not have match
7. RecyclerView asks Adapter to create ViewHolder
   adapter.createViewHolder()

1. While Layout Manager is calculating layout, it asks RecyclerView for View objects <
   recyclerView.getViewForPosition()
2. RecylcerView checks the Cache for a hit
   cache.getViewForPosition()
3. Cache does not have a view
4. RecyclerView asks adapter for View Type
   adapter.getViewType()
5. RecyclerView asks Pool for ViewHolder for type
   pool.getViewHolderByType()
6. Pool returns match
7. RecyclerView binds data
   adapter.bindViewHolder()
8. Recycler returns View to Layout Manager

1. Layout Manager tells RecyclerView the view has been added to layout
   addView
2. RecyclerView tells adapter
   onViewAttachedToWindow

1. Layout needs to remove a view, view is recycled.
   removeAndRecyclerView()
2. Tell Adapter to recycle view
   onViewDetachedFromWindow()
3. If view is valid for position, tell cache to hold iten.
4. Cache tells Pool if any older items are discarded.
5. Pool tells Adapter if any items are discarded.
   ViewHolder can discard its contents to save memory.

1. Layout Manager does not need all of the views.
   For example item is deleted
2. Each unused view is added to hidden adapter list
   this allows itemAnimator to perform animations on them such as fade out.
3. When itemAnimator is done, it tells Adapter
   onViewDetachedFromWindow
4. Causing recycler to update cache and recycle unused item.

When layout does not need view, and the view has a transient state (such as fading out) it can't be reused, so ask adapter.
onFailedToRecyle()
Adapter can reset the state of the ViewHolder and return it or not.

Pool has a fixed size per type and if full, the viewHolder will be discarded.

Generally happens if you animate all items, cause it doubles the number of items to do a cross fade.

ItemAnimator

Child Helper

Child helper decides which views to return to layout to support conditions such as add or remove by managing an alternate adapter which may have items which are in the process of being added or delete and the animation will fade them in or out.

Adapter Helper

Adapter helper keeps a virtual list of add and remove positions to help compute correct items in list.

Item Decorations

RecycledViewPool

Drag and Drop

Tips and Tricks