LINE Developer Meetup in Osaka #31

1. Create your DSL with Kotlin

2. 自己紹介
汪 永興
LINE Fukuoka 株式会社
開発Cチーム所属
Kotlinが大好きです
ワン ヨンシン (Freddie)

3. Create your DSL with Kotlin
Agenda
・What’s DSL
・Why Kotlin is easy to create DSL
・The ”Setting UI” DSL

4. Create your DSL with Kotlin
Domain Specific Language
・It is specialized to a particular application domain
Purpose

5. Create your DSL with Kotlin
Why DSL
• Improve Development Productivity
• Flexible design
• Code readability

6. Create your DSL with Kotlin
DSL in real world
・SQL
・Regular Expression
・Gradle

7. Create your DSL with Kotlin
Kotlin DSL in real world
• anko
• kotlintest
• Spring Framework

8. Why Kotlin is easy to
create DSL

9. Create your DSL with Kotlin
Main features in Kotlin
To support creating DSL easily
• Extension
• Higher-Order functions
• Lambda with receiver

10. Create your DSL with Kotlin
Extension
fun Context.getResIdFromAttr(attr: Int): Int {
val value = TypedValue()
theme.resolveAttribute(attr, value, true)
return value.resourceId
}
val resId = context.getResIdFromAttr(R.attr.selectableItemBacktround)
fun Context.getResIdFromAttr(attr: Int): Int {
val value = TypedValue()
theme.resolveAttribute(attr, value, true)
return value.resourceId
}
fun Context.getResIdFromAttr(attr: Int): Int {
val value = TypedValue()
theme.resolveAttribute(attr, value, true)
return value.resourceId
}

11. Create your DSL with Kotlin
Higher-Order functions
Takes functions as parameter
fun <T> lock(lock: Lock, body: () -> T): T {
lock.lock()
try {
return body()
} finally {
lock.unlock()
}
}
val result = lock (lock, { someResources.operation() } )

12. Create your DSL with Kotlin
Lambda with receiver
fun buildString(action: StringBuilder.() -> Unit): String {
val sb = StringBuilder()
sb.action()
return sb.toString()
}
buildString {// It is syntax sugar for lambda parameter
this.append(“test”)
this.append(“test”) //’this’ is StringBuilder
}
fun buildString(action: StringBuilder.() -> Unit): String {
val sb = StringBuilder()
sb.action()
return sb.toString()
}

13. The Setting DSL

14. Create your DSL with Kotlin
Characteristic of Setting UI
・Structured items
・Variable appearance

15. Create your DSL with Kotlin

16. Create your DSL with Kotlin
The syntax
settings {
settingGroup {
settingItem {
…
}
…
}
}
settings {
settingGroup {
settingItem {
…
}
…
}
}
settings {
settingGroup {
settingItem {
…
}
…
}
}
Rule1: settings is the root of the UI layoutRule2: settings includes settingGroupRule3: settingGroup includes settingItem

17. Create your DSL with Kotlin
Setting
class Settings(ctx: Context) : _ScrollView(ctx) {
internal val rootContainer = verticalLayout().lparams(width = matchParent, height = wrapContent)
fun addGroup(group: SettingGroup) {
rootContainer.addView(group)
}
}

18. Create your DSL with Kotlin
Rule1
inline fun ViewManager.settings(init: Settings.() -> Unit): Setting {
…
val settings = Settings(ctx)
settings.init()
this.addView(settings)
return settings
}
inline fun ViewManager.settings(init: Settings.() -> Unit): Setting {
…
val settings = Settings(ctx)
settings.init()
this.addView(settings)
return settings
}
inline fun ViewManager.settings(init: Settings.() -> Unit): Setting {
…
val settings = Settings(ctx)
settings.init()
this.addView(settings)
return settings
}
settings { //init()
settingGroup {
settingItem {
…
}
…
}
}

19. Create your DSL with Kotlin
SettingGroup
class SettingGroup(ctx: Context) : _LinearLayout(ctx) {
var title: String
…
}

20. Create your DSL with Kotlin
Rule2
inline fun Settings.settingGroup(init: SettingGroup.() -> Unit): SettingGroup {
val settingGroup = SettingGroup(this.context)
settingGroup.init()
…
this.addGroup(settingGroup)
return settingGroup
}
inline fun Settings.settingGroup(init: SettingGroup.() -> Unit): SettingGroup {
val settingGroup = SettingGroup(this.context)
settingGroup.init()
…
this.addGroup(settingGroup)
return settingGroup
}
inline fun Settings.settingGroup(init: SettingGroup.() -> Unit): SettingGroup {
val settingGroup = SettingGroup(this.context)
settingGroup.init()
…
this.addGroup(settingGroup)
return settingGroup
}

21. Create your DSL with Kotlin
SettingItem
class SettingItem(ctx: Context, …) : _LinearLayout(ctx) {
var leftIconResId: Int?
var rightIconResId: Int?
var title: String
var description: String
…
}

22. Create your DSL with Kotlin
Rule3
inline fun SettingGroup.settingItem(…, init: SettingItem.() -> Unit): SettingItem {
…
val settingItem = SettingItem(ctx, …)
settingItem.init()
this.addView(settingItem)
return settingItem
}
inline fun SettingGroup.settingItem(…, init: SettingItem.() -> Unit): SettingItem {
…
val settingItem = SettingItem(ctx, …)
settingItem.init()
this.addView(settingItem)
return settingItem
}
inline fun SettingGroup.settingItem(…, init: SettingItem.() -> Unit): SettingItem {
…
val settingItem = SettingItem(ctx, …)
settingItem.init()
this.addView(settingItem)
return settingItem
}

23. Create your DSL with Kotlin
DEMO Time!
https://github.com/wangyung/android-setting-ui-dsl

24. Create your DSL with Kotlin
Summary
・It is very easy to create custom DSL with Kotlin
・We can use DSL to write readable, maintainable code very easily

25. Q&A