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LITHO: BEST PRACTICES FOR BUILDING EFFICIENT UI Sergey Ryabov Facebook

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WHAT IS LITHO

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WHAT IS LITHO

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WHAT IS LITHO Declarative API

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WHAT IS LITHO Declarative API Asynchronous layout

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WHAT IS LITHO Declarative API Asynchronous layout Flatter view hierarchies

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WHAT IS LITHO Declarative API Asynchronous layout Flatter view hierarchies Fine-grained recycling

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@LayoutSpec object ListItemSpec { @OnCreateLayout fun onCreateLayout( c: ComponentContext, @Prop title: String, @Prop subtitle: String ): Component { return Column.create(c) .child( Text.create(c) .text(title)) .child( Text.create(c) .text(subtitle)) .build() } }

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@LayoutSpec object ListItemSpec { @OnCreateLayout fun onCreateLayout( c: ComponentContext, @Prop title: String, @Prop subtitle: String ): Component { return Column.create(c) .child( Text.create(c) .text(title)) .child( Text.create(c) .text(subtitle)) .build() } }

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@LayoutSpec object ListItemSpec { @OnCreateLayout fun onCreateLayout( c: ComponentContext, @Prop title: String, @Prop subtitle: String ): Component { return Column.create(c) .child( Text.create(c) .text(title)) .child( Text.create(c) .text(subtitle)) .build() } }

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@LayoutSpec object ListItemSpec { @OnCreateLayout fun onCreateLayout( c: ComponentContext, @Prop title: String, @Prop subtitle: String ): Component { return Column.create(c) .child( Text.create(c) .text(title)) .child( Text.create(c) .text(subtitle)) .build() } }

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@LayoutSpec object ListItemSpec { @OnCreateLayout fun onCreateLayout( c: ComponentContext, @Prop title: String, @Prop subtitle: String ): Component { return Column.create(c) .child( Text.create(c) .text(title)) .child( Text.create(c) .text(subtitle)) .build() } }

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@LayoutSpec object ListItemSpec { @OnCreateLayout fun onCreateLayout( c: ComponentContext, @Prop title: String, @Prop subtitle: String ): Component { return Column.create(c) .child( Text.create(c) .text(title)) .child( Text.create(c) .text(subtitle)) .build() } }

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@LayoutSpec object ListItemSpec { @OnCreateLayout fun onCreateLayout( c: ComponentContext, @Prop title: String, @Prop subtitle: String ): Component { return Column.create(c) .child( Text.create(c) .text(title)) .child( Text.create(c) .text(subtitle)) .build() } }

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@LayoutSpec object ListItemSpec { @OnCreateLayout fun onCreateLayout( c: ComponentContext, @Prop title: String, @Prop subtitle: String ): Component { return Column.create(c) .child( Text.create(c) .text(title)) .child( Text.create(c) .text(subtitle)) .build() } }

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@LayoutSpec object ListItemSpec { @OnCreateLayout fun onCreateLayout( c: ComponentContext, @Prop title: String, @Prop subtitle: String ): Component { return Column.create(c) .child( Text.create(c) .text(title)) .child( Text.create(c) .text(subtitle)) .build() } } class MainActivity : AppCompatActivity() { override fun onCreate(state: Bundle?) { super.onCreate(savedInstanceState) val c = ComponentContext(this) setContentView(LithoView.create(c, ListItem.create(c) .title("Title") .subtitle("Subtitle") .build())) } }

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@LayoutSpec object ListItemSpec { @OnCreateLayout fun onCreateLayout( c: ComponentContext, @Prop title: String, @Prop subtitle: String ): Component { return Column.create(c) .child( Text.create(c) .text(title)) .child( Text.create(c) .text(subtitle)) .build() } } class MainActivity : AppCompatActivity() { override fun onCreate(state: Bundle?) { super.onCreate(savedInstanceState) val c = ComponentContext(this) setContentView(LithoView.create(c, ListItem.create(c) .title("Title") .subtitle("Subtitle") .build())) } }

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@LayoutSpec object ListItemSpec { @OnCreateLayout fun onCreateLayout( c: ComponentContext, @Prop title: String, @Prop subtitle: String ): Component { return Column.create(c) .child( Text.create(c) .text(title)) .child( Text.create(c) .text(subtitle)) .build() } } class MainActivity : AppCompatActivity() { override fun onCreate(state: Bundle?) { super.onCreate(savedInstanceState) val c = ComponentContext(this) setContentView(LithoView.create(c, ListItem.create(c) .title("Title") .subtitle("Subtitle") .build())) } }

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@LayoutSpec object ListItemSpec { @OnCreateLayout fun onCreateLayout( c: ComponentContext, @Prop title: String, @Prop subtitle: String ): Component { return Column.create(c) .child( Text.create(c) .text(title)) .child( Text.create(c) .text(subtitle)) .build() } } class MainActivity : AppCompatActivity() { override fun onCreate(state: Bundle?) { super.onCreate(savedInstanceState) val c = ComponentContext(this) setContentView(LithoView.create(c, ListItem.create(c) .title("Title") .subtitle("Subtitle") .build())) } }

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@LayoutSpec object ListItemSpec { @OnCreateLayout fun onCreateLayout( c: ComponentContext, @Prop title: String, @Prop subtitle: String ): Component { return Column.create(c) .child( Text.create(c) .text(title)) .child( Text.create(c) .text(subtitle)) .build() } } class MainActivity : AppCompatActivity() { override fun onCreate(state: Bundle?) { super.onCreate(savedInstanceState) val c = ComponentContext(this) setContentView(LithoView.create(c, ListItem.create(c) .title("Title") .subtitle("Subtitle") .build())) } }

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@LayoutSpec object ListItemSpec { @OnCreateLayout fun onCreateLayout( c: ComponentContext, @Prop title: String, @Prop subtitle: String ): Component { return Column.create(c) .child( Text.create(c) .text(title)) .child( Text.create(c) .text(subtitle)) .build() } }

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@LayoutSpec object ListItemSpec { @OnCreateLayout fun onCreateLayout( c: ComponentContext, @Prop title: String, @Prop subtitle: String ): Component { return Column.create(c) .child( Text.create(c) .text(title)) .child( Text.create(c) .text(subtitle)) .build() } } @LayoutSpec object ListItemWithImageSpec { @OnCreateLayout fun onCreateLayout( c: ComponentContext, @Prop(resType=DRAWABLE) image: Drawable, @Prop title: String, @Prop subtitle: String): Component { return Row.create(c) .child( Image.create(c) .drawable(image)) .child( ListItem.create(c) .title(title) .subtitle(subtitle)) .build() } }

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@LayoutSpec object ListItemSpec { @OnCreateLayout fun onCreateLayout( c: ComponentContext, @Prop title: String, @Prop subtitle: String ): Component { return Column.create(c) .child( Text.create(c) .text(title)) .child( Text.create(c) .text(subtitle)) .build() } } @LayoutSpec object ListItemWithImageSpec { @OnCreateLayout fun onCreateLayout( c: ComponentContext, @Prop(resType=DRAWABLE) image: Drawable, @Prop title: String, @Prop subtitle: String): Component { return Row.create(c) .child( Image.create(c) .drawable(image)) .child( ListItem.create(c) .title(title) .subtitle(subtitle)) .build() } }

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@LayoutSpec object ListItemSpec { @OnCreateLayout fun onCreateLayout( c: ComponentContext, @Prop title: String, @Prop subtitle: String ): Component { return Column.create(c) .child( Text.create(c) .text(title)) .child( Text.create(c) .text(subtitle)) .build() } } @LayoutSpec object ListItemWithImageSpec { @OnCreateLayout fun onCreateLayout( c: ComponentContext, @Prop(resType=DRAWABLE) image: Drawable, @Prop title: String, @Prop subtitle: String): Component { return Row.create(c) .child( Image.create(c) .drawable(image)) .child( ListItem.create(c) .title(title) .subtitle(subtitle)) .build() } }

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@LayoutSpec object ListItemSpec { @OnCreateLayout fun onCreateLayout( c: ComponentContext, @Prop title: String, @Prop subtitle: String ): Component { return Column.create(c) .child( Text.create(c) .text(title)) .child( Text.create(c) .text(subtitle)) .build() } } @LayoutSpec object ListItemWithImageSpec { @OnCreateLayout fun onCreateLayout( c: ComponentContext, @Prop(resType=DRAWABLE) image: Drawable, @Prop title: String, @Prop subtitle: String): Component { return Row.create(c) .child( Image.create(c) .drawable(image)) .child( ListItem.create(c) .title(title) .subtitle(subtitle)) .build() } }

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HOW DOES IT ALL WORK?

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HOW DOES IT ALL WORK

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HOW DOES IT ALL WORK 1. Create an Internal Tree

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HOW DOES IT ALL WORK 1. Create an Internal Tree 2. Create LayoutState

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HOW DOES IT ALL WORK 1. Create an Internal Tree 2. Create LayoutState 3. Mount LayoutState

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@LayoutSpec object ListItemWithImageSpec { @OnCreateLayout fun onCreateLayout( c: ComponentContext, @Prop(resType=DRAWABLE) image: Drawable, @Prop title: String, @Prop subtitle: String): Component { return Row.create(c) .child( Image.create(c) .drawable(image)) .child( ListItem.create(c) .title(title) .subtitle(subtitle)) .build() } }

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@LayoutSpec object ListItemWithImageSpec { // ... Row.create(c) .child( Image.create(c) .drawable(image)) .child( ListItem.create(c) .title(title) .subtitle(subtitle)) .build() } }

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@LayoutSpec object ListItemWithImageSpec { // ... Row.create(c) .child( Image.create(c) .drawable(image)) .child( ListItem.create(c) .title(title) .subtitle(subtitle)) .build() } }

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@LayoutSpec object ListItemWithImageSpec { // ... Row.create(c) .child( Image.create(c) .drawable(image)) .child( ListItem.create(c) .title(title) .subtitle(subtitle)) .build() } } ListItemWithImage

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@LayoutSpec object ListItemWithImageSpec { // ... Row.create(c) .child( Image.create(c) .drawable(image)) .child( ListItem.create(c) .title(title) .subtitle(subtitle)) .build() } } Row ListItemWithImage

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@LayoutSpec object ListItemWithImageSpec { // ... Row.create(c) .child( Image.create(c) .drawable(image)) .child( ListItem.create(c) .title(title) .subtitle(subtitle)) .build() } } Row ListItemWithImage

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@LayoutSpec object ListItemWithImageSpec { // ... Row.create(c) .child( Image.create(c) .drawable(image)) .child( ListItem.create(c) .title(title) .subtitle(subtitle)) .build() } } Row ListItemWithImage Image

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@LayoutSpec object ListItemWithImageSpec { // ... Row.create(c) .child( Image.create(c) .drawable(image)) .child( ListItem.create(c) .title(title) .subtitle(subtitle)) .build(). } } Row ListItemWithImage Image

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@LayoutSpec object ListItemWithImageSpec { // ... Row.create(c) .child( Image.create(c) .drawable(image)) .child( ListItem.create(c) .title(title) .subtitle(subtitle)) .build(). } } Row ListItemWithImage Image ListItem

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Row ListItemWithImage Image ListItem ListItem.create(c) .title(title) .subtitle(subtitle)) .build(). } } @LayoutSpec object ListItemSpec { // ... Column.create(c) .child( Text.create(c) .text(title)) .child( Text.create(c) .text(subtitle)) .build() } }

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Row ListItemWithImage Image Column ListItem @LayoutSpec object ListItemSpec { // ... Column.create(c) .child( Text.create(c) .text(title)) .child( Text.create(c) .text(subtitle)) .build() } }

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Row ListItemWithImage Image Column ListItem @LayoutSpec object ListItemSpec { // ... Column.create(c) .child( Text.create(c) .text(title)) .child( Text.create(c) .text(subtitle)) .build() } }

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Row ListItemWithImage Image Column ListItem Text @LayoutSpec object ListItemSpec { // ... Column.create(c) .child( Text.create(c) .text(title)) .child( Text.create(c) .text(subtitle)) .build() } }

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Row ListItemWithImage Image Column ListItem Text @LayoutSpec object ListItemSpec { // ... Column.create(c) .child( Text.create(c) .text(title)) .child( Text.create(c) .text(subtitle)) .build() } }

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Row ListItemWithImage Image Column ListItem Text Text @LayoutSpec object ListItemSpec { // ... Column.create(c) .child( Text.create(c) .text(title)) .child( Text.create(c) .text(subtitle)) .build() } }

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Row ListItemWithImage Image Column ListItem Text Text @LayoutSpec object ListItemSpec { // ... Column.create(c) .child( Text.create(c) .text(title)) .child( Text.create(c) .text(subtitle)) .build() } }

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CREATE LAYOUTSTATE Row Image Column Text Text

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CREATE LAYOUTSTATE Measure with Yoga Row Image Column Text Text

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CREATE LAYOUTSTATE Measure with Yoga Row Image Column Text Text (0, 0 - 640, 96) (88, 0 - 640, 96) (16, 16 - 80, 80) (88, 16 - 624, 48) (88, 48 - 624, 80)

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CREATE LAYOUTSTATE Measure with Yoga Collect a list of items to be drawn and their positions Row Image Column Text Text (0, 0 - 640, 96) (88, 0 - 640, 96) (16, 16 - 80, 80) (88, 16 - 624, 48) (88, 48 - 624, 80)

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Row Image Column Text Text (0, 0 - 640, 96) (88, 0 - 640, 96) (16, 16 - 80, 80) (88, 16 - 624, 48) (88, 48 - 624, 80)

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Row Image Column Text Text (0, 0 - 640, 96) (88, 0 - 640, 96) (16, 16 - 80, 80) (88, 16 - 624, 48) (88, 48 - 624, 80) Root

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Root Row Image Column Text Text (0, 0 - 640, 96) (88, 0 - 640, 96) (16, 16 - 80, 80) (88, 16 - 624, 48) (88, 48 - 624, 80)

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Root Row Image Column Text Text (0, 0 - 640, 96) (88, 0 - 640, 96) (16, 16 - 80, 80) (88, 16 - 624, 48) (88, 48 - 624, 80)

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Root Image Row Image Column Text Text (0, 0 - 640, 96) (88, 0 - 640, 96) (16, 16 - 80, 80) (88, 16 - 624, 48) (88, 48 - 624, 80)

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Root Image Row Image Column Text Text (0, 0 - 640, 96) (88, 0 - 640, 96) (16, 16 - 80, 80) (88, 16 - 624, 48) (88, 48 - 624, 80)

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Root Image Row Image Column Text Text (0, 0 - 640, 96) (88, 0 - 640, 96) (16, 16 - 80, 80) (88, 16 - 624, 48) (88, 48 - 624, 80)

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Root Text Image Row Image Column Text Text (0, 0 - 640, 96) (88, 0 - 640, 96) (16, 16 - 80, 80) (88, 16 - 624, 48) (88, 48 - 624, 80)

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Root Text Image Row Image Column Text Text (0, 0 - 640, 96) (88, 0 - 640, 96) (16, 16 - 80, 80) (88, 16 - 624, 48) (88, 48 - 624, 80)

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Root Text Image Row Image Column Text Text (0, 0 - 640, 96) (88, 0 - 640, 96) (16, 16 - 80, 80) (88, 16 - 624, 48) (88, 48 - 624, 80) Text

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Root Text Image Row Image Column Text Text (0, 0 - 640, 96) (88, 0 - 640, 96) (16, 16 - 80, 80) (88, 16 - 624, 48) (88, 48 - 624, 80) Text Im ageDraw able TextDraw able TextDraw able

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Root Text Image Row Image Column Text Text (0, 0 - 640, 96) (88, 0 - 640, 96) (16, 16 - 80, 80) (88, 16 - 624, 48) (88, 48 - 624, 80) Text Im ageDraw able TextDraw able TextDraw able LayoutState

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MOUNT LAYOUTSTATE Root Text Image Text Im ageDraw able TextDraw able TextDraw able LayoutState

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MOUNT LAYOUTSTATE The only step that always happens on UI thread Root Text Image Text Im ageDraw able TextDraw able TextDraw able LayoutState

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Root Text Image Text Im ageDraw able TextDraw able TextDraw able LayoutState Row Image Column Text Text

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@MountSpec object GradientSpec { @OnCreateMountContent fun onCreateMountContent(context: Context): GradientDrawable { return GradientDrawable( ) } @OnMount fun onMount( c: ComponentContext, drawable: GradientDrawable, @Prop @ColorInt colors: IntArray) { drawable.colors = colors } // ... }

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@MountSpec object GradientSpec { @OnCreateMountContent fun onCreateMountContent(context: Context): GradientDrawable { return GradientDrawable( ) } @OnMount fun onMount( c: ComponentContext, drawable: GradientDrawable, @Prop @ColorInt colors: IntArray) { drawable.colors = colors } // ... }

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@MountSpec object GradientSpec { @OnCreateMountContent fun onCreateMountContent(context: Context): GradientDrawable { return GradientDrawable( ) } @OnMount fun.onMount( c: ComponentContext, drawable: GradientDrawable, @Prop @ColorInt colors: IntArray) { drawable.colors = colors } // ... }

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@MountSpec object GradientSpec { @OnCreateMountContent fun onCreateMountContent(context: Context): GradientDrawable { return GradientDrawable( ) } @OnMount fun.onMount( c: ComponentContext, drawable: GradientDrawable, @Prop @ColorInt colors: IntArray) { drawable.colors = colors } // ... }

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public @interface MountSpec { int poolSize() default.3; boolean isPureRender() default false; }

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public @interface MountSpec { int poolSize() default.3; boolean isPureRender() default false; }

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public @interface MountSpec { int poolSize() default.3; boolean isPureRender() default false; }

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public @interface MountSpec { int poolSize() default 3; boolean isPureRender() default false; } @MountSpec(poolSize = 30, isPureRender = true) class ImageSpec {

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OPTIMIZATIONS

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OPTIMIZATIONS Layout/Mount Diffing

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OPTIMIZATIONS Layout/Mount Diffing • Reuse Measurements

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OPTIMIZATIONS Layout/Mount Diffing • Reuse Measurements • Reuse LayoutOutputs

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Text Img Text (16, 16 - 80, 80) (88, 16 - 624, 48) (88, 48 - 624, 80) (16, 16 - 80, 80) (88, 16 - 624, 48) (88, 48 - 624, 80) Internal Tree Diff Tree

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Text Img Text (16, 16 - 80, 80) (88, 16 - 624, 48) (88, 48 - 624, 80) (16, 16 - 80, 80) (88, 16 - 624, 48) (88, 48 - 624, 80) Internal Tree Diff Tree

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Text Img Text (16, 16 - 80, 80) (88, 16 - 624, 48) (88, 48 - 624, 80) (16, 16 - 80, 80) (88, 16 - 624, 48) (88, 48 - 624, 80) Internal Tree Diff Tree

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Text Img Text (16, 16 - 80, 80) (88, 16 - 624, 48) (88, 48 - 624, 80) (16, 16 - 80, 80) (88, 16 - 624, 48) (88, 48 - 624, 80) Internal Tree Diff Tree

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(16, 16 - 80, 80) (88, 16 - 624, 48) (88, 48 - 624, 80) Text Text Img (16, 16 - 80, 80) (88, 16 - 624, 48) (88, 48 - 624, 80) Root LayoutState Internal Tree Diff Tree

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(16, 16 - 80, 80) (88, 16 - 624, 48) (88, 48 - 624, 80) (16, 16 - 80, 80) (88, 16 - 624, 48) (88, 48 - 624, 80) Root Text Text Image LayoutState Internal Tree Diff Tree

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OPTIMIZATIONS Layout/Mount Diffing • Reuse Measurements • Reuse LayoutOutputs

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OPTIMIZATIONS Layout/Mount Diffing • Reuse Measurements • Reuse LayoutOutputs IncrementalMount

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INCREMENTAL MOUNT

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INCREMENTAL MOUNT

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INCREMENTAL MOUNT

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INCREMENTAL MOUNT

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INCREMENTAL MOUNT

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INCREMENTAL MOUNT

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GOTCHAS

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GOTCHAS Use isPureRender / @ShouldUpdate to reuse previous layout results

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GOTCHAS Use isPureRender / @ShouldUpdate to reuse previous layout results Tweak MountPools according to you requirements

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MANAGING STATE

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@OnCreateLayout fun onCreateLayout( c: ComponentContext, @State count: Int): Component { return Column.create(c) .child( Text.create(c) .text("$count") ) .child( Text.create(c) .text("+") ) .build() }

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@OnCreateLayout fun onCreateLayout( c: ComponentContext, @State count: Int): Component { return Column.create(c) .child( Text.create(c) .text("$count") ) .child( Text.create(c) .text("+") ) .build() }

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 @OnUpdateState fun increment(count: StateValue) { count.set(count.get() + 1) }

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 @OnUpdateState fun increment(count: StateValue) { count.set(count.get() + 1) }
 
 @OnEvent(ClickEvent::class) fun.onIncrement(c: ComponentContext) { RootComponent.increment(c) }

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 @OnUpdateState fun increment(count: StateValue) { count.set(count.get() + 1) }
 
 @OnEvent(ClickEvent::class) fun.onIncrement(c: ComponentContext) { RootComponent.increment(c) } // ... .child( Text.create(c) .text("+") .clickHandler(RootComponent.onIncrement(c)) )

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@OnUpdateState fun increment(count: StateValue) { count.set(count.get() + 1) }
 
 @OnEvent(ClickEvent::class) fun.onIncrement(c: ComponentContext) { RootComponent.increment(c) }

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@OnUpdateState fun increment(count: StateValue) { count.set(count.get() + 1) }
 
 RootComponent.increment(c)

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@OnUpdateState fun increment(count: StateValue) { count.set(count.get() + 1) }
 
 RootComponent.increment(c) 
 RootComponent.incrementSync(c)

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State updates? I'll take two!

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@OnUpdateState fun changeColor(color: StateValue, @Param newColor: Color) { color.set(newColor) } @OnUpdateState fun changeName(name: StateValue, @Param newName: String) { name.set(newName) }

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@OnUpdateState fun changeColor(color: StateValue, @Param newColor: Color) { color.set(newColor) } @OnUpdateState fun changeName(name: StateValue, @Param newName: String) { name.set(newName) } ... ... RootComponent.changeColor(c, Color.BLUE) RootComponent.changeName(c, "Plum")

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@OnUpdateState fun changeColor(color: StateValue, @Param newColor: Color) { color.set(newColor) } @OnUpdateState fun changeName(name: StateValue, @Param newName: String) { name.set(newName) } ... ... RootComponent.changeColor(c, Color.BLUE) RootComponent.changeName(c, "Plum")

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@OnUpdateState fun changeFruit( color: StateValue, name: StateValue, @Param newColor: Color, @Param newName: String) { color.set(newColor) name.set(newName) } ... ... RootComponent.changeFruit(c, Color.BLUE, "Plum")

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What if State is not tied to rendering?

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@OnCreateLayout fun onCreateLayout( c: ComponentContext, @State count: Int, ): Component { return Column.create(c) // ... .build() }

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@OnCreateLayout fun onCreateLayout( c: ComponentContext, @State count: Int, @State(canUpdateLazily = true) step: Int ): Component { return Column.create(c) // ... .child( TextInput.create(c).initialText("$step")) .build() }

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@State(canUpdateLazily = true) step: Int RootComponent.lazyUpdateStep(c, value)

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@State(canUpdateLazily = true) step: Int RootComponent.lazyUpdateStep(c, value)

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Can I use State for caching?

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@OnCalculateCachedValue(name = "heavyConfig") fun onCalculateHeavyConfig(@Prop prop: Long): HeavyConfig { return calculateHeavyConfig(prop) } @OnCreateLayout fun onCreateLayout( c: ComponentContext, @Prop prop: Long, @CachedValue heavyConfig: HeavyConfig @State state: Boolean): Component { return ... }

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@OnCalculateCachedValue(name = "heavyConfig") fun onCalculateHeavyConfig(@Prop prop: Long): HeavyConfig { return calculateHeavyConfig(prop) } @OnCreateLayout fun onCreateLayout( c: ComponentContext, @Prop prop: Long, @CachedValue heavyConfig: HeavyConfig @State state: Boolean): Component { return ... }

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GOTCHAS

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GOTCHAS Batch your State updates

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GOTCHAS Batch your State updates Use lazy State updates where possible

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GOTCHAS Batch your State updates Use lazy State updates where possible Use CachedValues for heavy lifting

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ANIMATE ALL THE THINGS

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@OnCreateLayout fun onCreateLayout( c: ComponentContext, @State alignToEnd: Boolean): Component { val align = if (alignToEnd) FLEX_END else FLEX_START return Column.create(c) .justifyContent(CENTER) .child( Button.create(c) .text("Catch me!") .alignSelf(align) .clickHandler(RootComponent.onClick(c)) ) .build() }

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@OnCreateLayout fun onCreateLayout( c: ComponentContext, @State alignToEnd: Boolean): Component { val align = if (alignToEnd) FLEX_END else FLEX_START return Column.create(c) .justifyContent(CENTER) .child( Button.create(c) .text("Catch me!") .transitionKey("button") .alignSelf(align) .clickHandler(RootComponent.onClick(c)) ) .build() }

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@OnCreateLayout fun onCreateLayout( c: ComponentContext, @State alignToEnd: Boolean): Component { val align = if (alignToEnd) FLEX_END else FLEX_START return Column.create(c) .justifyContent(CENTER) .child( Button.create(c) .text("Catch me!") .transitionKey("button") .alignSelf(align) .clickHandler(RootComponent.onClick(c)) ) .build() } @OnCreateTransition fun.onCreateTransition(c: ComponentContext): Transition { return.Transition.create("button") .animate(AnimatedProperties.X) }

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@OnCreateLayout fun onCreateLayout( c: ComponentContext, @State alignToEnd: Boolean): Component { val align = if (alignToEnd) FLEX_END else FLEX_START return Column.create(c) .justifyContent(CENTER) .child( Button.create(c) .text("Catch me!") .transitionKey("button") .alignSelf(align) .clickHandler(RootComponent.onClick(c)) ) .build() } @OnCreateTransition fun.onCreateTransition(c: ComponentContext): Transition { return.Transition.create("button") .animate(AnimatedProperties.X) }

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@OnCreateTransition fun.onCreateTransition(c: ComponentContext): Transition { return.Transition.create("button") .animate(AnimatedProperties.X) }

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@OnCreateTransition fun.onCreateTransition(c: ComponentContext): Transition { return.Transition.allLayout() }

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ANIMATIONS

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ANIMATIONS onCreateTransition is called on every onCreateLayout

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ANIMATIONS onCreateTransition is called on every onCreateLayout Even if you don't need to animate that specific UI update

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ANIMATIONS onCreateTransition is called on every onCreateLayout Even if you don't need to animate that specific UI update More granular control?

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@OnCreateTransition fun onCreateTransition(c: ComponentContext): Transition { return Transition.allLayout() }

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@OnCreateTransition fun onCreateTransition(c: ComponentContext, @Prop prop: Diff, @State state: Diff): Transition? { return if (shouldAnimate(prop, state)) Transition.allLayout() else null }

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@OnUpdateState fun updateAlignment(alignToEnd: StateValue) { alignToEnd.set(!alignToEnd.get()) }

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@OnUpdateStateWithTransition fun updateAlignment(alignToEnd: StateValue): Transition { alignToEnd.set(!alignToEnd.get()) return Transition.create("button") .animate(AnimatedProperties.X) }

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GOTCHAS

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GOTCHAS Use Diff for more granular control over transitions

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GOTCHAS Use Diff for more granular control over transitions Can use @OnUpdateStateWithTransition if animating only State changes

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GRADUAL ADOPTION

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GRADUAL ADOPTION

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GRADUAL ADOPTION Can't migrate the whole screen at once? Do step by step:

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GRADUAL ADOPTION Can't migrate the whole screen at once? Do step by step: • Complex UI parts can be replaced with a LithoView and underlying Component structure

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GRADUAL ADOPTION Can't migrate the whole screen at once? Do step by step: • Complex UI parts can be replaced with a LithoView and underlying Component structure • Custom Views can be wrapped in MountSpecs

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ADVANCED CONFIGURATION

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COMPONENTTREE BUILDER

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COMPONENTTREE BUILDER Set of advanced settings val tree = ComponentTree.create(c) // ... .build() lithoView.componentTree = tree

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COMPONENTTREE BUILDER Set of advanced settings • LayoutHandler val tree = ComponentTree.create(c) .layoutThreadHandler(lithoHandler) .build() lithoView.componentTree = tree

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COMPONENTTREE BUILDER Set of advanced settings • LayoutHandler • Reconciliation val tree = ComponentTree.create(c) .isReconciliationEnabled(true) .build() lithoView.componentTree = tree

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SOMETHING DOESN'T WORK!

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TOOLS

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TOOLS Yoga Playground

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yogalayout.com/playground

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TOOLS Yoga Playground Flipper + Layout plugin

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fbflipper.com

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TOOLS Yoga Playground Flipper + Layout plugin Litho IntelliJ Plugin (Beta)

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github.com/facebook/litho/tree/master/litho-intellij-plugin

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TOOLS Yoga Playground Flipper + Layout plugin Litho IntelliJ Plugin (Beta) Lithography Sample app

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RESOURCES Official Docs: fblitho.com Intro to Litho: youtu.be/uzCK4Vnme7o Lithography Sample app: github.com/facebook/litho/tree/master/sample Litho Codelabs (early preview): github.com/facebook/litho/tree/master/codelabs Dive into Litho Threading Model: youtu.be/78BUH1LZaZ4

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THANK YOU Sergey Ryabov @colriot