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Smoother Android development with Kotlin
Márton Braun • AutSoft • [email protected]
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Android APIs are sometimes hard to use
Kotlin allows us to reshape existing API
Extension functions and properties
Named and default parameters
Operator overloading
Lambdas, higher order functions, and inline functions
Everyone has their own collection of utilities…
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Google takes a stance, creates their own
First appeared Feb 2, 2018
Goals
Only provide uniquely Kotlin APIs
Don’t provide new implementation, just new syntax
Minimize overhead, focus on zero overhead abstractions
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No content
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Extension properties
view.setVisibility(View.VISIBLE)
view.visibility = View.VISIBLE
view.isVisible = true
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Default and named parameters
view.setPadding(20, view.topPadding,
20, view.bottomPadding)
view.updatePadding(left = 20, right = 20)
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Operator overloading and extension functions
linearLayout.addView(view)
linearLayout += view
linearLayout.removeView(view)
linearLayout -= view
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Higher order, inline extension functions
for (i in 0 until linearLayout.childCount) {
val view = linearLayout.get(i)
Timber.d(view.tag)
}
linearLayout.forEach { view ->
Timber.d(view.tag)
}
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Extension functions
val bitmap = Bitmap.createBitmap(
view.width, view.height, Bitmap.Config.ARGB_8888)
view.draw(Canvas(bitmap))
val bitmap = view.toBitmap()
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Operator overloading
val color = bitmap.getPixel(100, 50)
val color = bitmap[100, 50]
bitmap.setPixel(100, 50, color)
bitmap[100, 50] = color
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Extension functions, default parameters
Toast.makeText(this, "Hello world", Toast.LENGTH_SHORT)
.show()
toast("Hello world")
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Extension functions, default parameters
Toast.makeText(this, "Hello world", Toast.LENGTH_LONG)
.show()
toast("Hello world", duration = Toast.LENGTH_LONG)
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Higher order, inline extension functions
sharedPreferences.edit()
.putBoolean("drawerOpened", true)
.apply()
sharedPreferences.edit {
putBoolean("drawerOpened", true)
}
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Higher order, inline extension functions
db.beginTransaction()
db.insert("users", null, values)
db.setTransactionSuccessful()
db.endTransaction()
db.transaction {
insert("users", null, values)
}
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inline fun SQLiteDatabase.transaction(...): T {
beginTransaction()
try {
val result = body()
setTransactionSuccessful()
return result
} finally {
endTransaction()
}
}
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Destructuring
val lat = location.latitude
val lon = location.longitude
val (lat, lon) = location
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Explore Android KTX yourself and use it in your projects
https://github.com/android/android-ktx/
https://android.github.io/android-ktx/core-ktx/
Write your own extensions for APIs that don’t fit your needs
If these are on Android, consider submitting a PR to Android KTX