Jetpack Compose is a new UI toolkit for Android that uses a declarative paradigm where the UI is defined as a function of app state, rather than as interacting objects. It allows defining UI using Kotlin instead of XML layouts. Compose provides composable functions to build UI in a declarative way and allows observing state changes. However, Compose is still in early development and requires unreleased versions of Android Studio, Kotlin, and the Android Gradle plugin to use.

1. Jetpack Compose
#KotlinEverywhere Android Development
Lutas Lin

2. What is Jetpack Compose?
• Is a Kotlin Compiler Plugin
• Is a new UI Toolkit
• Declarative UI
• Unbundle from OS
• Pre-Alpha

5. Declarative UI
Flutter Swift UI

6. Compose Hello World
@Composable
fun Hello() {
MaterialTheme {
Text(text = "Hello")
}
}

7. UI as Function
• View / Xml -> UI as Object
• Compose -> UI as Function

8. UI = f(s)

9. UI = f(s)
Composable function
State

10. How to use Jetpack
Compose?
• https://adambennett.dev/2019/10/jetpack-compose-now-on-maven/
• Android Studio Version >= 3.5.1
// Use Jvm 1.8
compileOptions {
sourceCompatibility JavaVersion.VERSION_1_8
targetCompatibility JavaVersion.VERSION_1_8
}
kotlinOptions {
jvmTarget = "1.8"
}
// Kotlin Reflect
implementation “org.jetbrains.kotlin:kotlin-reflect"
// Compose
kapt "androidx.compose:compose-compiler:0.1.0-dev01"
implementation "androidx.compose:compose-runtime:0.1.0-dev02"
// Compose UI
implementation "androidx.ui:ui-core:0.1.0-dev02"
implementation "androidx.ui:ui-layout:0.1.0-dev02"
implementation "androidx.ui:ui-material:0.1.0-dev01"

11. But…Something Broken?
• @Model observing失效了了！！！
Compose requires:
• An unreleased version of the Android Gradle Plugin
• An unreleased version of Android Studio
• An unreleased EAP version of Kotlin
• Build via AOSP
• https://engineering.q42.nl/try-jetpack-compose-today/

12. Sample

14. State
• https://youtu.be/VsStyq4Lzxo?t=1541

15. Good and Bad

16. What Next?
• Kotlin/Compose vs Dart/Flutter ?
• What’s new in Jetpack Compose (https://
developer.android.com/dev-summit/schedule/day1)