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Ryota Niinomi
How to notify
Dataset changed for
RecyclerView
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Ryota Niinomi
@AWA
@r21nomi
r21nomi
Android Developer / Creative Coder / Anime Lover
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What I talk today
Think about a better way to
notify dataset changed
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Agenda
• Adapter.notify~()
• DiffUtil
• Paging Library
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Adapter.notify~()
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• notifyDataSetChanged()
• notifyItemRange~()
• notifyItem~()
Adapter.notify~()
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notifyDataSetChanged()
• Easy
• Redraw all
• No animation
Adapter.notify~()
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notifyItemRange~()
• Redraw target items
• Animation
• Not only target items
notifyItemRange~()
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Not only target items
Adapter.notify~()
A
B
C
D
B,C is also redrawn
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notifyItem~()
• Simple use of notifyItemRange~()
• A bit messy
Adapter.notify~()
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notifyItem~()
adapter.getDataSet().removeAt(position)
adapter.notifyItemRemoved(position)
// ok
adapter.getDataSet().removeAt(position2)
adapter.notifyItemRemoved(position2)
// Unintended item is removed
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adapter.getDataSet().removeAt(position)
adapter.notifyItemRemoved(position)
adapter.notifyItemRangeChanged(
position,
adapter.itemCount - position
)
adapter.getDataSet().removeAt(position2)
adapter.notifyItemRemoved(position2)
adapter.notifyItemRangeChanged(…)
notifyItem~()
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adapter.getDataSet().removeAt(position)
adapter.notifyItemRemoved(position)
adapter.notifyItemRangeChanged(
position,
adapter.itemCount - position
)
// ok
adapter.getDataSet().removeAt(position2)
adapter.notifyItemRemoved(position2)
adapter.notifyItemRangeChanged(…)
// ok
notifyItem~()
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Ideal
• Easy to use
• Redraw only changed items
• Multiple item notifying
• Animation
Adapter.notify~()
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DiffUtil
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DiffUtil
• Support Lib 25.1.0~
• Calculate diff between 2 list
• Notify only changed items
• Animation
DiffUtil
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Implementation
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Implementation For DiffUtil
• DiffUtil.Callback
• DiffUtil.calculateDiff()
• diffResult.dispatchUpdatesTo()
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DiffUtil.Callback
override fun getOldListSize() = oldList.size
override fun getNewListSize() = newList.size
// Same item?
override fun areItemsTheSame(oldPos: Int, newPos: Int): Boolean {
return oldList[oldPos].id == newList[newPos].id
}
// Any changes?
override fun areContentsTheSame(oldPos: Int, newPos: Int): Boolean {
val old = oldList[oldPos]
val new = newList[newPos]
return old == new
}
Implementation For DiffUtil
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DiffUtil.Callback
true
false
false
true
areItemsTheSame
areContentsTheSame
Do not redraw
redraw
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Calculate Diff
val diffResult = DiffUtil.calculateDiff(diffCallback)
Implementation For DiffUtil
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Notify
val diffResult = DiffUtil.calculateDiff(diffCallback)
diffResult.dispatchUpdatesTo(adapter)
Implementation For DiffUtil
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Full Implementation
val diffCallback = object : DiffUtil.Callback() {
val oldList = currentDataSet
val newList = newDataSet
override fun getOldListSize() = oldList.size
override fun getNewListSize() = newList.size
override fun areItemsTheSame(oldPos: Int, newPos: Int): Boolean
= oldList[oldPos].id == newList[newPos].id
override fun areContentsTheSame(oldPos: Int, newPos: Int): Boolean
= oldList[oldPos] == newList[newPos]
}
val diffResult = DiffUtil.calculateDiff(diffCallback)
diffResult.dispatchUpdatesTo(adapter)
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old list new list
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assistant-sdk-python
android-audio-high-perfor
gmail-add-ons-samples
apps-script-oauth2
android-CustomChoiceList
android-ndk
Log of
onBindViewHolder()
old list new list
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assistant-sdk-python
android-audio-high-perfor
gmail-add-ons-samples
apps-script-oauth2
android-CustomChoiceList
android-ndk
Log of
onBindViewHolder()
old list new list
are not redrawn
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Calculate diff on background
“If the lists are large,
this operation may take significant time”
“run this on a background thread,
get the DiffUtil.DiffResult
then apply it on the main thread”
Implementation For DiffUtil
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Calculate diff on background
Thread({
val diffCallback = object : DiffUtil.Callback() {
…
}
// Calculate diff on background thread.
val diffResult = DiffUtil.calculateDiff(diffCallback)
handler.post {
// Update on main thread.
diffResult.dispatchUpdatesTo(adapter)
}
}).start()
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Calculate diff on background
Thread({
val diffCallback = object : DiffUtil.Callback() {
…
}
// Calculate diff on background thread.
val diffResult = DiffUtil.calculateDiff(diffCallback)
handler.post {
// Update on main thread.
diffResult.dispatchUpdatesTo(adapter)
}
}).start()
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Calculate diff on background
Thread({
val diffCallback = object : DiffUtil.Callback() {
…
}
// Calculate diff on background thread.
val diffResult = DiffUtil.calculateDiff(diffCallback)
handler.post {
// Update on main thread.
diffResult.dispatchUpdatesTo(adapter)
}
}).start()
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Paging Library
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Paging Library
Paging Library
• Part of AAC
• Having same feature as DiffUtil
• Paging
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Data Flow
Paging Library
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Structure
Paging Library
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Implementation
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Specification
Implementation for Paging Library
• Getting data from Github API
• Sort
• Paging
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DataSource
Implementation for Paging Library
• Source of paged data
• Database, On Memory, API
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class PageKeyedRepoDataSource: PageKeyedDataSource() {
override
fun loadInitial(params: LoadInitialParams,
callback: LoadInitialCallback) {
// Initial data fetching
}
override
fun loadBefore(params: LoadParams,
callback: LoadCallback) {
// no-op
}
override
fun loadAfter(params: LoadParams,
callback: LoadCallback) {
// Paged data fetching
}
}
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override
fun loadInitial(params: LoadInitialParams,
callback: LoadInitialCallback) {
val page = 1
val nextPageKey = 2
val response = repoApiClient
.getRepos(USER_NAME, page, params.requestedLoadSize)
.execute()
callback.onResult(response.body(), null, nextPageKey)
}
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override
fun loadAfter(params: LoadParams,
callback: LoadCallback) {
val page = params.key
val nextPageKey = params.key + 1
val response = repoApiClient
.getRepos(USER_NAME, page, params.requestedLoadSize)
.execute()
callback.onResult(response.body(), nextPageKey)
}
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DataSource.Factory
Implementation for Paging Library
• Factory class return DataSource
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class RepoDataFactory: DataSource.Factory {
override fun create(): DataSource {
return object : PageKeyedDataSource() {
...
}
}
}
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LivePagedListBuilder
Implementation for Paging Library
• Return PagedList as LiveData
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val dataSourceFactory = RepoDataFactory(repoApiClient)
val config = PagedList.Config.Builder()
.setInitialLoadSizeHint(10)
.setPageSize(10)
.build()
return LivePagedListBuilder(dataSourceFactory, config)
.setBackgroundThreadExecutor(NETWORK_IO)
.build()
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private fun getRepos(): LiveData> {
...
}
getRepos()
.observe(context, Observer { pagedList ->
// Items are drawn
pagedListAdapter.setList(pagedList)
})
Observe PagedList
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Update DataSet
Implementation for Paging Library
• Re-fetch API with sort condition
• Update items only changed by
setting PagedList again
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private fun getRepos(condition: SortCondition)
: LiveData> {
...
}
getRepos(SortCondition.UPDATED)
.observe(context, Observer { pagedList ->
// Only new items are drawn
repoAdapter.setList(pagedList)
})
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private fun getRepos(condition: SortCondition)
: LiveData> {
...
}
getRepos(SortCondition.UPDATED)
.observe(context, Observer { pagedList ->
repoAdapter.setList(null)
// All new items are redrawn
repoAdapter.setList(pagedList)
})
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More DataSource
Implementation for Paging Library
• API
• Room
• Room + API
• Other
← This time
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Conclusion
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Conclusion
• Consider the cost of redrawing
• Use DiffUtil
• Paging Library might be better
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https://github.com/r21nomi/RecyclerView-DiffUtil-Sample
r21nomi/RecyclerView-DiffUtil-Sample
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Thank you
@r21nomi
r21nomi