Connect Recharge: What does Recomposition mean to your app?

LITE version

PRESENTED AT:
Connect Recharge 2022

https://hopin.com/events/connect-recharge-2022/registration?code=wwK1JKQKXBSzI6RaQZcehxqtr

DESCRIPTION:
You’ve heard a lot that Jetpack Compose is a declarative UI toolkit and it recomposes only the components that changed. But what does it exactly mean? How does it apply not only in the scale of one composable function but the entire app? Well, it turns out there is more than meets the eye when it comes to recomposition, and in this talk, we will deep dive into its benefits, costs, and gotchas. You’ll learn some practical tips to efficiently build functions in Jetpack Compose.

MORE TALKS & ARTICLES FROM ME: https://cupsofcode.com/talks/

Transcript

1. What does Recomposition mean to your app? Aida Issayeva Lite
2. About me 🤖 Android GDE 󰠁 Sr. Software Engineer 󰠅 Instructor 🐦 @aida_isay 🌐 cupsofcode.com 📽 @aida_isay
3. TODAY’S AGENDA 02 Smart Recomposition 03 Tools to detect & debug 04 Practical tips 05 01 What is Recomposition? Jetpack Compose Paradigm
4. Jetpack Compose paradigm UI widgets are functions They are stateless Different arguments, passed to the functions, trigger updates
5. SlotTable Android OS Composer Applier UI Node Tree State Snapshot System Change List Applier
6. 01 Jetpack Compose Paradigm Compose Phases 1 Composition Calls composable functions and creates a description of the UI 2 Layout Measures the layout elements and their children and places them on the screen 3 Drawing Draws the UI elements to the screen
7. Composition is a process of executing composable functions
8. SlotTable Android OS Com poser Applier UI Node Tree State Snapshot System Change List
9. What is recomposition?
10. Recomposition is a re-execution of composable functions in response to state changes
11. Recomposition in SlotTable: example 1 @Composable fun Card() { val counter = remember { mutableStateOf(0) } Column { Text(text = "Compose") Button(onClick = { counter.value++ }) { Text(text = "Click me $counter") } } } 02 What is recomposition Group(456) ….. Group(789) “Compose” Group(101) “Click me 0” C A R D C O L U M N B U T T O N { ... } Group(123) State(0) R E M E M B E R
12. Recomposition in SlotTable: example 1 @Composable fun Card() { val counter = remember { mutableStateOf(0) } Column { Text(text = "Compose") Button(onClick = { counter.value++ }) { Text(text = "Click me $counter") } } } 02 What is recomposition Group(456) ….. Group(789) “Compose” Group(101) “Click me 0” C A R D C O L U M N B U T T O N { ... } Group(123) State(0) R E M E M B E R
13. Recomposition in SlotTable: example 1 @Composable fun Card() { val counter = remember { mutableStateOf(0) } Column { Text(text = "Compose") Button(onClick = { counter.value++ }) { Text(text = "Click me $counter") } } } 02 What is recomposition Group(456) ….. Group(789) “Compose” Group(101) “Click me 1” C A R D C O L U M N B U T T O N { ... } Group(123) State(1) R E M E M B E R
14. Recomposition in SlotTable: example 2 @Composable fun Card() { val counter = remember { mutableStateOf(0) } Column { Text(text = "Compose $counter") Button(onClick = { counter.value++ }) { Text(text = "Click me") } } } 02 What is recomposition Group(456) ….. Group(789) “Compose 0” Group(101) “Click me” C A R D C O L U M N B U T T O N { ... } Group(123) State(0) R E M E M B E R
15. Recomposition in SlotTable: example 2 @Composable fun Card() { val counter = remember { mutableStateOf(0) } Column { Text(text = "Compose $counter") Button(onClick = { counter.value++ }) { Text(text = "Click me") } } } 02 What is recomposition Group(456) ….. Group(789) “Compose 1” Group(101) “Click me” C A R D C O L U M N B U T T O N { ... } Group(123) State(0) R E M E M B E R
16. 02 What is recomposition Compose Phases 1 Composition Calls composable functions and creates a description of the UI 2 Layout Measures the layout elements and their children and places them on the screen 3 Drawing Draws the UI elements to the screen
17. Smart recomposition
18. Inputs are stable Smart recomposition is an intelligent way to skip the recomposition of composable functions when their
19. Stable type contract rules: RULE 1 The result of calls for two instances to `equals()` function will always be the same for the same two instances RULE 2 When a public property of the type changes, Composition is notified RULE 3 All public properties of the type are also stable
20. Stable property types: Primitive types: Int, Boolean, Long, Char, Float String Annotated with @Stable
21. What about custom data types? 03 Smart Recomposition
22. Exceptions: 1. Enum 2. Enum Entry 3. Interface 4. Annotation 5. Companion Object 6. Inline 7. Anonymous object 8. Expect element 9. Inner class 03 Smart Recomposition Inferring Class stability • visits each eligible class • annotates with @StabilityInferred • helps compiler to determine what to recompose
23. Tools to detect & debug recomposition
24. 1. Recompose Highlighter ➢ Google Play team introduced the modifier ➢ Use this link below to check out the code snippet 04 Tools to detect
25. 2. Log Statements 04 Tools to detect ➢ Ancient and the most reliable. ➢ Android Studio Electric Eel has an automatic support for it. ➢ Wrapped as a modifier function. Check out the code snippet below
26. 3. Compose Compiler Metrics 04 Tools to detect { "skippableComposables" : 64, "restartableComposables" : 76, "readonlyComposables" : 0, "totalComposables" : 76 } ➢ Full analysis ➢ Restartable & !skippable = ⛳ ➢ Check out the code snippet below for integration details
27. Practical tips to leverage smart recomposition
28. 1. Break down composable functions /** * 👍 : only associated column with changes gets recomposed. */ @Composable fun GoodGreetingsTip1() { Column { Greeting("Android", 1, Gray200) Greeting("Compose", 2, Brown200) } } @Composable fun Greeting(name: String, columnNumber: Int, background: Color) { Column { . . . } } 05 Practical tips
29. 2. Use the key composable /** * 👍 : the key is set, and when item in the middle is removed, only LazyColumn gets recomposed * and not its children */ @Composable fun GoodGreetingsTip2(fruits: List<String>) { LazyColumn( modifier = Modifier .recompositionCounter("lazyColumn") ) { items( items = fruits, key = { it } ) { fruit -> Item(fruit) } } } 05 Practical tips
30. 3. Read the state value at the lowest composable function /** * 👍 : only inner column and its children get recomposed, because the read happens * in one of the children. */ @Composable fun GoodGreetingsTip3(cardInfo: () -> CardInfo) { Column { UpperRow() GoodRow(cardInfo = cardInfo) } } @Composable private fun GoodRow(cardInfo: () -> CardInfo) { Row { GoodInnerColumn(cardInfo = cardInfo) } } 05 Practical tips
31. 4. Use modifier lambdas /** * 👍: With the receiver lambda function (Modifier.offset{}) in place, this composable function doesn't get recomposed. */ @Composable private fun GoodGreetingsTip4(yAxis: () -> Int) { Row( modifier = Modifier .offset { IntOffset(y = yAxis(), x = 0) }, verticalAlignment = Alignment.Bottom ) { . . . } } 05 Practical tips
32. IMPORTANT 1 Move any logic out of the composable functions to viewmodels, presenters, etc 5. Tips worth re-repeating IMPORTANT 2 Don’t create dependable composable functions on the result of other composables functions IMPORTANT 3 Avoid any side-effects in the composable functions, because they can run in parallel
33. Resources 1. Jetpack Compose Internals 2. Jetpack Compose source code 3. Understanding Jetpack Compose — part 1 of 2 4. Understanding Jetpack Compose — part 2 of 2 5. Recomposition made easy 6. RecomposeHighlighter code snippet 7. Compose Compiler Metrics 8. A historical introduction to the Compose reactive state model 9. What is “donut-hole” skipping in Jetpack Compose? 10. Compose performance 11. Composable Metrics 12. Thinking in Compose 13. Jetpack Compose Phases 14. Jetpack Compose Lifecycle Resources Recomposition tips code samples
34. THANK YOU www.cupsofcode.com Code | Live | Grow @aida_isay