Reducing boilerplate with Kotlin, KTX and Kotlin Android Extensions

Reducing boilerplate w/
Kotlin,
KTX &
Kotlin Android Extensions
author: Patrick P Steiger
Software Engineer @ CESAR

Structure
0. Motivation
1. Kotlin Idioms
2. Kotlin Android Extensions
3. KTX

Motivation
Reduce boilerplate code
… But why?

Motivation
… But why?
1. Do the same w/ less typing

Motivation
… But why?
2. > LOC, > BUGS!
(Steve McConnell, Code Complete)

Motivation
KISS principle
design principle noted by the U.S. Navy in 1960.
most systems work best if they are kept simple
rather than made complicated; therefore
simplicity should be a key goal in design, and that
unnecessary complexity should be avoided.

Motivation
less is more
Proverb.
That which is less complicated is often better understood and
more appreciated than what is more complicated;
simplicity is preferable to complexity;
brevity in communication is more effective than verbosity.

Motivation
"A designer knows he has achieved perfection not when there is
nothing left to add, but when there is nothing left to take away."
- Antoine de Saint-Exupery
“... a substantial number of the problems caused by buggy software
occurs because vendors keep adding more and more features to their
programs, which inevitably means more code and thus more bugs.”
- Andrew Tannenbaum

Kotlin Idioms
00. Substitute returns for assignments
fun sum(a: Int, b: Int): Int {
return a+b
}
fun sum(a: Int, b: Int): Int = a+b

Kotlin Idioms
01. Omit return types
fun sum(a: Int, b: Int): Int = a+b
fun sum(a: Int, b: Int) = a+b

Kotlin Idioms
!!, ? - Kotlin Answer to NPE hell
(it’s safer && terser)

Kotlin Idioms
02. Avoid Java’s excessive null checks
02.0. Define non-nullable vars
val aCounter: Int = 0 // does NOT accept null
aCounter = null // CRASH in compile time (better than run time!)
●Error:(9, 8) Null can not be a value of a non-null type Int

Kotlin Idioms
02. Avoid Java’s excessive null checks
02.1. Define nullable vars, but avoid ‘if’ checks
val aCounter: Int? = 0 // Nullable
aCounter = null // OK!
aCounter?.let { // alternative to if (aCounter != null) {
anotherInt += it // anotherInt += aCounter
} // }
anotherInt += aCounter // OOPS - doesn’t compile - var can be null
anotherInt += aCounter!! // compiles. ‘!!’ means “I’m SURE it’s not null”

Kotlin Idioms
03. Avoid repeating yourself
fun aFunc(aView: View?): View? {
if (aView != null) {
aView.text = “A text”
aView.setBackgroundColor(Color.parseColor(“#000000”))
aView.setElevation(1f)
}
return aView
}
aView?.run { // aView becomes ‘this’ if not null
text = “A text” // this.text, this is omitted
setBackgroundColor(Color.parseColor(“#000000”))
setElevation(1f)
}
return aView
}

Kotlin Idioms
}
return aView
}
fun aFunc(aView: View?) { // omit return type
aView?.run { // aView becomes ‘this’ if not null
setElevation(1f)
}
return aView
}

Kotlin Idioms
}
return aView
}
fun aFunc(aView: View?) = aView?.run { // aView becomes ‘this’ if not null
setElevation(1f)
}

Kotlin Idioms
03. Avoid repeating yourself - return ‘when’ expressions
fun foo(color: String): Int {
var result: Int = 0
if (color == “Red”) {
result = 10
} else if (color == “Green”) {
result = 11
} else if (color == “Blue”) {
result = 12
}
return result
}
fun foo(color: String) = when (color) {
"Red" -> 10
"Green" -> 11
"Blue" -> 12
else -> 0
}

Kotlin Idioms
03. Avoid repeating yourself - return ‘when’ expressions
fun transform(color: String) {
if (color == “Red”) {
return 0
} else if (color == “Green”) {
return 1
} else if (color == “Blue”) {
return 2
} else {
throw IllegalArgumentException("Invalid color param value”)
}
}
fun transform(color: String) = when (color) {
"Red" -> 0
"Green" -> 1
"Blue" -> 2
else -> throw IllegalArgumentException("Invalid color param value”)
}

Kotlin Idioms
AlertDialog.Builder builder = new AlertDialog.Builder(getActivity());
builder.setMessage(getResources().getString(R.string.gps_network_not_enabled));
builder.setPositiveButton(getResources().getString(R.string.ok)), new DialogInterface.OnClickListener() {
public void onClick(DialogInterface dialog, int id) {
startActivity(Intent(ACTION_LOCATION_SOURCE_SETTINGS));
}
});
builder.show();
AlertDialog.Builder(activity).apply {
setMessage(resources.getString(R.string.gps_network_not_enabled))
setPositiveButton(resources.getString(R.string.ok)) { _, _ ->
startActivity(Intent(ACTION_LOCATION_SOURCE_SETTINGS))
}
show()
}

Forget findViewById Forever

on build.gradle:
apply plugin: 'kotlin-android-extensions'
on activity:
import kotlinx.android.synthetic.main.<layout>.*
on fragment:
import kotlinx.android.synthetic.main.<layout>.view.*

class MyActivity : Activity() {
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
setContentView(R.layout.activity_main)
val textView1 = findViewById(R.id.textView1) as TextView
textView1.setText("Hello")
textView2.setText("world!")
}
}

import kotlinx.android.synthetic.main.activity_main.*
class MyActivity : Activity() {
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
setContentView(R.layout.activity_main)
textView1.setText("Hello")
textView2.setText("world!")
}
}

What about Fragments?
import kotlinx.android.synthetic.main.the_fragment_layout.view.*
class AppListFragment : Fragment() {
override fun onCreateView(inflater: LayoutInflater, container: ViewGroup?, savedInstanceState: Bundle?):
View? = inflater.inflate(R.layout.fragment_app_list, container, false)
override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
welcomeMessage.text = "Hello Kotlin!"
}
}
there is a welcomeMessage id in fragment_app_list XML

Android KTX
“Android KTX is a set of Kotlin extensions that is part of the
Android Jetpack family. It optimizes Jetpack and Android
platform APIs for Kotlin use.”

Android KTX
Project’s build.gradle
repositories {
google()
}
App’s build.gradle
dependencies {
implementation 'androidx.core:core-ktx:1.0.0'
}

Android KTX
animatorInstance.addListener(object: Animator.AnimatorListener {
override fun onAnimationRepeat(animator: Animator?) {
// onRepeat behavior
}
override fun onAnimationEnd(animator: Animator?) {
// onEnd behavior
}
override fun onAnimationCancel(animator: Animator?) {
// onCancel behavior
}
override fun onAnimationStart(animator: Animator?) {
// onStart behavior
}
})

Android KTX
animatorInstance.doOnEnd {
// onEnd behaviour
}

Android KTX
val bundle = Bundle()
bundle.putString(ARG_TEMPLATE_TYPE, templateType.name)
bundle.putString(ARG_TEMPLATE_DESC, templateType.desc)
With KTX:
val bundle = bundleOf( // map syntax
ARG_TEMPLATE_TYPE to templateType.name,
ARG_TEMPLATE_DESC to templateType.desc
)

Android KTX
private fun viewToBitmap(view: View): Bitmap {
// 1 Create a new bitmap with the view info
val bitmap = Bitmap.createBitmap(view.width, view.height, Bitmap.Config.ARGB_8888)
// 2 Draw the view pixes into the bitmap
val canvas = Canvas(bitmap)
view.draw(canvas)
return bitmap
}
With KTX:
private fun viewToBitmap(view: View) = view.drawToBitmap() // implicit return

Android KTX
if (view.getVisibility() == View.INVISIBLE) // int
view.setVisibility(View.VISIBLE)
With KTX:
if (!view.isVisible) // boolean
view.isVisible = true

Android KTX
SharedPreferences.Editor editor = getSharedPreferences(MY_PREFS_NAME, MODE_PRIVATE).edit();
editor.putString("key1", "value");
editor.putInt("key2", 1);
editor.apply();
With KTX:
import androidx.core.content.edit
getSharedPreferences(MY_PREFS_NAME, MODE_PRIVATE).edit {
putString("key1", "value")
putInt("key2", 1)
}

Summing up...
Kotlin wants you to do more and type less
This shows in its nature, syntax and libraries

References
Kotlin Idioms https://kotlinlang.org/docs/reference/idioms.html
Kotlin Android Extensions https://kotlinlang.org/docs/tutorials/android-plugin.html
Android KTX https://developer.android.com/kotlin/ktx

Thank you
contact: psteiger@gmail.com

Reducing boilerplate with Kotlin, KTX and Kotlin Android Extensions

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