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KOTLIN EXTENSIONS AND
HIGHER ORDER FUNCTIONS
JITIN SHARMA
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WHAT ARE EXTENSION FUNCTIONS
▸ Extensions are functions which can be added to existing
classes(not really)
▸ Black magic == Static functions
▸ Less power than member functions
▸ They are meant to remove Utils like classes.
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fun Double.toFahrenheit() : Double = (this * 1.8) + 32
val f = 34.toFahrenheit() //call like this
fun Boolean.toString() : String = "abc"
true.toString() //"true"
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fun Double.toFahrenheit() : Double = (this * 1.8) + 32
val f = 34.toFahrenheit() //call like this
fun Boolean.toString() : String = "abc"
true.toString() //"true"
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HIGHER ORDER FUNCTIONS
▸ Hail lambdas
▸ Functionception - Function as a parameter of function and
returning a function
▸ Functions can be passed around as objects
▸ Bonus Point: SAM conversions for Java Interfaces
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HOW TO
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KOTLIN 101 - REMOVE THEM NULL CHECKS
▸ if (someObject != null) { }
▸ someObject?.let { it-> }
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WORK WITH `APPLY`!
supportActionBar?.apply {
setDisplayHomeAsUpEnabled(true)
setDisplayShowHomeEnabled(true)
}
// Use apply to avoid repetition of calling variable
// Combine with and apply
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WORK WITH `APPLY`!
supportActionBar?.apply {
setDisplayHomeAsUpEnabled(true)
setDisplayShowHomeEnabled(true)
}
fun addTintWithCompat(drawable: Drawable, colorInt: Int): Drawable {
return with(drawable) {
DrawableCompat.wrap(drawable).apply {
DrawableCompat.setTint(this, colorInt)
}
}
}
// Use apply to avoid repetition of calling variable
// Combine with and apply
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WORK `WITH` APPLY!
// Insert functional programming here :)
fun movieListReducer(action: Action, movieListState: MovieListState?):
MovieListState {
return with(movieListState) {
val state = movieListState ?: MovieListState()
when (action) {
is displayMovies -> {
state.copy(movieObjects = action.movieObjects)
}
else -> state
}
}
}
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KOTLIN LIBRARIES
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KOTLIN LIBRARIES
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KOTLIN LIBRARIES
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CODE VISIBILITY FOOTPRINT
▸ Koltin can help in reducing visible
code by wrapping around functions.
▸ You can move away functions which
are not important from visibility
point of view.
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DO IT EFFICIENTLY
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DO IT EFFICIENTLY
Move away methods
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DIY
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DO IT YOURSELF
// interface for item click
// initialize interface
// setting interface method on click
// getting on click in main class
JAVA WAY
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DO IT YOURSELF
// Add a function in parameter of adapter constructor
// Invoke listener inside on click
// Access listener as lambda in main class
KOTLIN WAY
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inline fun justTry(block: () -> T) = try {
block()
} catch (_: Throwable) { // log here }
GENERAL FUNCTIONALITIES
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inline fun justTry(block: () -> T) = try {
block()
} catch (_: Throwable) { // log here }
GENERAL FUNCTIONALITIES
fun String.toIntOrZero() : Int {
var value = 0
justTry {
value = this.toInt()
}
return value
}
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inline fun debugMode(block : () -> Unit) {
if (BuildConfig.DEBUG) { block() }
}
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debugMode {
StrictMode
.setThreadPolicy(StrictMode.ThreadPolicy.Builder()
.detectAll()
.penaltyLog()
.build())
}
inline fun debugMode(block : () -> Unit) {
if (BuildConfig.DEBUG) { block() }
}
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GOT INTERNET?
if (isNetworkStatusAvailable()) {
val apiService = ApiClient.client?.create(ApiInterface::class.java)
val call = apiService?.discoverMovies(API_KEY)
call?.enqueue(this)
}
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GOT INTERNET?
if (isNetworkStatusAvailable()) {
val apiService = ApiClient.client?.create(ApiInterface::class.java)
val call = apiService?.discoverMovies(API_KEY)
call?.enqueue(this)
}
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GOT INTERNET?
val apiService = ApiClient.client?.create(ApiInterface::class.java)
val call = apiService?.discoverMovies(API_KEY)
call?.enqueue(this)
}
withConnection {
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asyncExecutor(
heavyFunction = { MovieApplication.movieDataBase?.movieDao()?.getAll() },
response = { response -> response?.forEach { /**/ }}
)
fun asyncExecutor(heavyFunction: () -> T, response : (response : T?) -> Unit) {
async(UI) {
val data : Deferred = bg { heavyFunction() }
response(data.await())
}
}
FUNCTIONS AS OBJECTS
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VISIBILITY EXTENSIONS
fun View.isVisibile(): Boolean = this.visibility == View.VISIBLE
fun View.makeVisible() { this.visibility = View.VISIBLE }
fun List.showViews() {
this.forEach { view -> view.makeVisible() }
}
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CONTEXT EXTENSIONS
fun Context.dpToPx(dp : Int): Float {
val displayMetrics = this.resources.displayMetrics
return Math.round(dp * (displayMetrics.xdpi / DisplayMetrics.DENSITY_DEFAULT)).toFloat()
}
fun Context.getColorCompat(@ColorRes colorInt: Int) : Int =
ContextCompat.getColor(this, colorInt)
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GENERAL EXTENSIONS
fun ByteArray.convertBytesToBitmap(): Bitmap =
BitmapFactory.decodeByteArray(this, 0, size)
fun Double.celsiusToFahrenheit() : Double = (this * 1.8) + 32
fun String.convertStringToDate(simpleDateFormatPattern: String): Date? {
val simpleDateFormat = SimpleDateFormat(simpleDateFormatPattern, Locale.getDefault())
var value: Date? = null
justTry {
value = simpleDateFormat.parse(this)
}
return value
}
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SYNTACTIC SUGARS CAN CAUSE DIABETES
▸ Good looking code may not always be best at performance.
▸ Look for downsides before writing a snippet whose usage
may get accelerated.
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DON’T JUDGE BOOK BY IT’S COVER
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PUTTING ON THE DETECTIVE HAT
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BACK TO JAVA WORLD
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GET IN-LINE
Kotlin’s doc for use of Inline Functions
Decompiled to Java
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WHEN CODING
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LOOK BEFORE CODE
▸ Analyze your code before jumping into code.
▸ Don’t over-engineer.
▸ You may not need extensions or higher order functions.
▸ Performance analyze your code.
▸ Examine before writing, the logic you just wrote may already be
present in existing libraries.
▸ Single parameter functions are best candidate for conversion to
extension function.
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CONTEXT EXTENSIONS IN FRAGMENTS AND ACTIVITIES
inline fun Context.withConnection(block: () -> Unit) {
if (isNetworkStatusAvailable()) { block() }
}
inline fun Fragment.withConnection(block: () -> Unit) {
this.context?.withConnection { block() }
}
// In Activity
withConnection { }
//Fragment
context?.withConnection {}
// In Fragment
withConnection { }
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JUST DON’T
fun debugOrElse(blockIf: () -> Unit, blockElse: () -> Unit) {
if (BuildConfig.DEBUG) { blockIf.invoke() }
else { blockElse.invoke() }
}
debugOrElse({ StrictMode.enableDefaults() },
{ Timber.plant(ReleaseTree())})
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JUST DON’T
fun debugOrElse(blockIf: () -> Unit, blockElse: () -> Unit) {
if (BuildConfig.DEBUG) { blockIf.invoke() }
else { blockElse.invoke() }
}
debugOrElse({ StrictMode.enableDefaults() },
{ Timber.plant(ReleaseTree())})
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JUST DON’T
fun debugOrElse(blockIf: () -> Unit, blockElse: () -> Unit) {
if (BuildConfig.DEBUG) { blockIf.invoke() }
else { blockElse.invoke() }
}
debugOrElse({ StrictMode.enableDefaults() },
{ Timber.plant(ReleaseTree())})
if (BuildConfig.DEBUG) {
StrictMode.enableDefaults()
} else {
Timber.plant(ReleaseTree())
}
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BE SMART - USE ANKO
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THAT’S IT
▸ https://github.com/jitinsharma/Kotlin.someExtensions
▸ https://android.jlelse.eu/playing-with-kotlin-higher-order-
functions-aecce3d72a12
▸ https://twitter.com/js_2892
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Q&A