Android with Kotlin

Slides from my talk Android with Kotlin at Oct 2017 GDG 6 October City, Egypt.

Transcript

1. Android with Kotlin a_tarek360 Oct, 2017
2. What is kotlin?
3. Kotlin is a Russian island
4. Kotlin • By JetBrains in 2011 • Open sourced in 2012 • The first officially stable release in 2016
5. At Google I/O 2017, Google announced..
6. Kotlin • Official Programming Language for Android Development
7. Kotlin • Statically typed programming language • 100% interoperable with Java and Android • Avoid entire classes of errors such as null pointer exceptions.
8. var / val var name = "Ahmed" val id = 1 Val cannot be reassigned id = 3
9. Null Safety Safe var name: String name = null // Compilation error Nullable val name: String? = null // Nullable type println(name.length()) // Compilation error println(name?.length())
10. Classes/Interfaces class SimpleClass class SimpleClass(value: String) interface SimpleInterface class SimpleClass : BaseClass(), SimpleInterface
11. Data Class data class Car( var name: String, var color: Int, var speed: Float) • No need to implement: toString, equals
12. Functions fun isMoving(speed: Int): Boolean { return speed > 0 } fun isMoving(speed: Int) = speed > 0
13. Companion Object class Car { companion object { fun drive() { } } } // Like calling a static method Car.drive()
14. Simple Android Activity class MainActivity : Activity() { override fun onCreate(savedInstanceState: Bundle?) { super.onCreate(savedInstanceState) val name = savedInstanceState?.getString("name") } }
15. Extending Language isLollipop { view.elevation = 3.0f } . . . . inline fun isLollipop(code: () -> Unit) { if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.LOLLIPOP) { code.invoke() } }
16. Smart Cast fun setData(view: View) { if (view is ImageView) { view.setImageDrawable(drawable) } if (view is TextView) { view.setText("hello") } }
17. Callback/Lambda • view.setOnClickListener(object : View.OnClickListener { override fun onClick(view: View?) { doSomething() } }) • view.setOnClickListener { view -> doSomething(view) } • view.setOnClickListener { doSomething() }
18. Function Parameter Default Value fun toast(message: String) { Toast.toast(this, message, Toast.LENGTH_LONG).show() } fun toast(message: String, duration: Int) { Toast.makeText(this, message, duration).show() } fun toast(message: String, duration: Int = Toast.LENGTH_LONG) { Toast.makeText(this, message, duration).show() }
19. Extension Functions fun Activity.toast(message: String, duration: Int = Toast.LENGTH_LONG) { Toast.makeText(this, message, duration).show() } // Call it from any activity instance toast("Hello World!") toast("Hello World!", Toast.LENGTH_SHORT)
20. Kotlin Android Extensions <RelativeLayout android:layout_width="match_parent" android:layout_height="match_parent"> <ImageView android:id="@+id/photo" … /> <TextView android:id="@+id/name" … /> </RelativeLayout>
21. Kotlin Android Extensions import kotlinx.android.synthetic.main.activity_main.* override fun onCreate(savedInstanceState: Bundle?) { super.onCreate(savedInstanceState) setContentView(R.layout.activity_main) photo.setImageBitmap(bitmap) name.setText("Hello World!") }
22. Thank You!