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MotionLayout & RecyclerView November 17th, 2020 @kaeawc Jason Pearson Principal Android Engineer @ Hinge

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Journey

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Journey

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Widgets

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Widgets

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Widgets

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Widgets

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Widgets

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0 20 40 60 80 100 ➟ Transition Motion Layout 2020 2018

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0 20 40 60 80 100 ➟ Transition Motion Layout 2020 2018 Two Years Ago...

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CoordinatorLayout + RecyclerView Complicated Layout Cancel SEND LIKE Saul Add a comment

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CoordinatorLayout + RecyclerView Complicated Layout Cancel SEND LIKE Saul Add a comment

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Cancel SEND LIKE Saul Add a comment Shared Element Exclusions, Delays, TransitionManager

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Hacky + Limited

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Hacky + Limited Need to Animate Even More

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So... what to do?

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Conventional wisdom said we're animating too much

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Is Android just not good enough?

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Existential doubt

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MotionLayout

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Coordination Gesture Support Interruptible Scrolling Support Ticked All the Boxes ✅ ✅ ✅ ✅

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So how do I build this?

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First let's look at requirements

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Configuration Changes Widgets

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Configuration Changes Widgets

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Configuration Changes Widgets

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Widgets Configuration Changes

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Widgets Configuration Changes Typing something interesting

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Widgets Flinging The user needs to be able to not just swipe from one item to the next, but fling through several items.

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Flinging The user needs to be able to not just swipe from one item to the next, but fling through several items.

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Scroll Position

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Scroll Position This introduces cases where the ViewHolder in question is partially off screen.

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Scroll Position This introduces cases where the ViewHolder in question is partially off screen.

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Scroll Position This introduces cases where the ViewHolder in question is partially off screen.

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Scroll Position This introduces cases where the ViewHolder in question is partially off screen.

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Heterogeneous

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Heterogeneous Not every ViewHolder is the same size or type of content. Some are only text, some are images and some are streaming video.

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Solutions

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Evolving Approaches

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Evolving Approaches

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Create placeholder by hand Evolving Approaches

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widget_photo_item.xml

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widget_text_item.xml

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activity_main.xml Component Tree

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FrameLayout activity_main.xml Component Tree

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activity_main.xml FrameLayout widgetList Component Tree

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android:layout_height="match_parent" tools:context=".MainActivity"> activity_main.xml FrameLayout widgetList Component Tree

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android:layout_height="match_parent" tools:context=".MainActivity"> activity_main.xml FrameLayout widgetList ConstraintLayout Component Tree

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android:layout_height="match_parent" tools:listitem="@layout/widget_photo_item" /> activity_main.xml FrameLayout widgetList ConstraintLayout Component Tree

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android:layout_height="match_parent" tools:listitem="@layout/widget_photo_item" /> activity_main.xml FrameLayout widgetList ConstraintLayout overlay Component Tree

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android:background="@color/overlayOnSurface" /> activity_main.xml FrameLayout widgetList ConstraintLayout overlay photoPlaceholder Component Tree

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android:background="@color/overlayOnSurface" /> activity_main.xml FrameLayout widgetList ConstraintLayout overlay photoPlaceholder textPlaceholder Component Tree

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android:layout_height="match_parent" tools:listitem="@layout/widget_photo_item" />

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android:layout_height="match_parent" tools:listitem="@layout/widget_photo_item" />

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android:layout_height="match_parent" tools:listitem="@layout/widget_photo_item" />

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android:layout_height="match_parent" tools:listitem="@layout/widget_photo_item" />

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activity_main.xml Component Tree FrameLayout widgetList ConstraintLayout overlay photoPlaceholder textPlaceholder

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activity_main.xml Component Tree FrameLayout widgetList overlay photoPlaceholder textPlaceholder constraintLayout

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activity_main.xml

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activity_main.xml

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activity_main.xml

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activity_main.xml

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activity_main.xml

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activity_main.xml

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activity_main.xml

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activity_main.xml

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activity_main.xml

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activity_main.xml

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main_scene.xml

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main_scene.xml

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main_scene.xml

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main_scene.xml

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main_scene.xml

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main_scene.xml

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main_scene.xml

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main_scene.xml

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main_scene.xml activity_main.xml

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Motion Layout end start activity_main.xml main_scene.xml

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0 20 40 60 80 100 ➟ Transition Motion Layout end start activity_main.xml main_scene.xml

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0 20 40 60 80 100 ➟ Transition Motion Layout end start activity_main.xml main_scene.xml

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Motion Layout activity_main.xml end start main_scene.xml

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activity_main.xml android:visibility="gone" > main_scene.xml

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class MainActivity : AppCompatActivity(R.layout.activity_main) { private val ui: ActivityMainBinding by lazy { ... } private var clicks = Channel(1) private var placeholderSource: ViewBinding? = null override fun onCreate(savedInstanceState: Bundle?) { super.onCreate(savedInstanceState) val view = ui.root setContentView(view) ui.widgetList.adapter = WidgetAdapter(clicks) } override fun onResume() { super.onResume() MainActivity.kt

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private var clicks = Channel(1) private var placeholderSource: ViewBinding? = null override fun onCreate(savedInstanceState: Bundle?) { super.onCreate(savedInstanceState) val view = ui.root setContentView(view) ui.widgetList.adapter = WidgetAdapter(clicks) } override fun onResume() { super.onResume() clicks.consumeAsFlow() .onEach { onWidgetTapped(getWidgetViewHolder(it)) } .launchIn(lifecycleScope) } private fun getWidgetViewHolder(position: Int): MainActivity.kt

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ui.widgetList.adapter = WidgetAdapter(clicks) } override fun onResume() { super.onResume() clicks.consumeAsFlow() .onEach { onWidgetTapped(getWidgetViewHolder(it)) } .launchIn(lifecycleScope) } private fun getWidgetViewHolder(position: Int): WidgetViewHolder<*>? { return ui.widgetList.activeViewHolders(onlyVisible = true) .filterIsInstance>() .firstOrNull { it.adapterPosition == position } } private fun onWidgetTapped(viewHolder: WidgetViewHolder<*>?) { if (viewHolder == null) return MainActivity.kt

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.firstOrNull { it.adapterPosition == position } } private fun onWidgetTapped(viewHolder: WidgetViewHolder<*>?) { if (viewHolder == null) return val placeholder = when (viewHolder) { is WidgetPhotoViewHolder -> { ui.textPlaceholder.root.isVisible = false ui.photoPlaceholder } is WidgetTextViewHolder -> { ui.photoPlaceholder.root.isVisible = false ui.textPlaceholder } else -> return } ui.motionLayout.enterPlaceholder( MainActivity.kt

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} else -> return } ui.motionLayout.enterPlaceholder( listView = ui.widgetList, source = viewHolder.binding, placeholder = placeholder, startState = R.id.list, endState = R.id.detail) placeholderSource = viewHolder.binding } override fun onBackPressed() { val source = placeholderSource if (source != null) { ui.motionLayout.exitPlaceholder(source) { placeholderSource = null } MainActivity.kt

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placeholderSource = viewHolder.binding } override fun onBackPressed() { val source = placeholderSource if (source != null) { ui.motionLayout.exitPlaceholder(source) { placeholderSource = null } ui.motionLayout.transitionToState(R.id.list) } else { super.onBackPressed() } } } MainActivity.kt

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fun MotionLayout.enterPlaceholder( listView: View, source: T, placeholder: T, startState: Int, endState: Int, completion: () -> Unit = {}) { // Create Bitmap from source Canvas // TODO: Very inefficient, please fix placeholder.applyBindingToPlaceholder(source) // Updates starting state with constraints that match the source val profileState = calculatePlaceholderConstraints(placeholder.root.id, source, listView) updateState(startState, profileState) setTransition(startState, endState) isVisible = true placeholder.root.isVisible = true MotionExtensions.kt MainActivity.kt

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startState: Int, endState: Int, completion: () -> Unit = {}) { // Create Bitmap from source Canvas // TODO: Very inefficient, please fix placeholder.applyBindingToPlaceholder(source) // Updates starting state with constraints that match the source val profileState = calculatePlaceholderConstraints(placeholder.root.id, source, listView) updateState(startState, profileState) setTransition(startState, endState) isVisible = true placeholder.root.isVisible = true after(completion) transitionToEnd() source.root.alpha = 0f } MotionExtensions.kt MainActivity.kt

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// Create Bitmap from source Canvas // TODO: Very inefficient, please fix placeholder.applyBindingToPlaceholder(source) // Updates starting state with constraints that match the source val profileState = calculatePlaceholderConstraints(placeholder.root.id, source, listView) updateState(startState, profileState) setTransition(startState, endState) isVisible = true placeholder.root.isVisible = true after(completion) transitionToEnd() source.root.alpha = 0f } MotionExtensions.kt MainActivity.kt

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Assessment

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✅ No delay to transition Assessment

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Assessment

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// Create Bitmap from source Canvas // TODO: Very inefficient, please fix placeholder.applyBindingToPlaceholder(source) Assessment

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Use RecyclerView internals to detach and use ViewHolders in MotionLayout temporarily Next Idea...

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LayoutManager detaching views ✅ No delay to transition ✅ Reusable ✅ Efficient

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LayoutManager detaching views ✅ No delay to transition ✅ Reusable ✅ Efficient ❌ Probably can't work with Exoplayer ❌ RecyclerView dependency

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Use MotionLayout internals for attribute copying Next Idea

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fun MotionLayout.enterPlaceholder( listView: View, source: T, placeholder: T, startState: Int, endState: Int, completion: () -> Unit = {}) { // Create Bitmap from source Canvas // TODO: Very inefficient, please fix placeholder.applyBindingToPlaceholder(source) // Updates starting state with constraints that match the source val profileState = calculatePlaceholderConstraints(placeholder.root.id, source, listView) updateState(startState, profileState) setTransition(startState, endState) isVisible = true placeholder.root.isVisible = true MotionExtensions.kt

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source: T, placeholder: T, startState: Int, endState: Int, completion: () -> Unit = {}) { // Create Bitmap from source Canvas // TODO: Very inefficient, please fix placeholder.applyBindingToPlaceholder(source) // Updates starting state with constraints that match the source val profileState = calculatePlaceholderConstraints(placeholder.root.id, source, listView) updateState(startState, profileState) setTransition(startState, endState) isVisible = true placeholder.root.isVisible = true MotionExtensions.kt

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source: T, placeholder: T, startState: Int, endState: Int, completion: () -> Unit = {}) { // Copy attributes from source placeholder.applyBindingToPlaceholder(source) // Updates starting state with constraints that match the source val profileState = calculatePlaceholderConstraints(placeholder.root.id, source, listView) updateState(startState, profileState) setTransition(startState, endState) isVisible = true placeholder.root.isVisible = true after(completion) MotionExtensions.kt

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Assessment

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Assessment ✅ No delay to transition ✅ Robust ✅ Reusable Efficient?

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Motion Layout Assessment ✅ No delay to transition ✅ Robust ✅ Reusable Efficient?

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Motion Layout Assessment ✅ No delay to transition ✅ Robust ✅ Reusable ✅ Efficient enough for now

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Motion Layout

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Motion Layout

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Motion Layout

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Motion Layout grind

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Motion Layout grind

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Motion Layout grind

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Motion Layout grind

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Motion Layout grind

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Motion Layout grind

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Motion Layout grind

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Motion Layout fun grind

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Motion Layout fun grind

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Questions? @kaeawc Slides will be posted: https://bit.ly/2Uxq4VU

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http://bit.ly/dcsf19-adv-motionlayout Questions? @kaeawc