My first Android app with Kotlin

Intro slides for the workshop 'My first Android app with Kotlin'
More info: https://github.com/lgvalle/androidkotlinworkshop

Transcript

1. My first Android app with Kotlin https://github.com/lgvalle/androidkotlinworkshop Luis G. Valle - @lgvalle
2. #SVQTECH
3. JVM https://kotlinlang.org
4. 1. Efficiency 2. Read-only variables 3. Null-safety 4. Smart Cast 5. Higher-order functions 6. Extension functions Why should you care?
5. 1. Efficiency fun sum(a: Int, b: Int): Int { return a + b }
6. 1. Efficiency fun sum(a: Int, b: Int): Int = a + b
7. 1. Efficiency fun sum(a: Int, b: Int) = a + b
8. 2. Read-only variables val a: Int = 1 // Read-only Int val b = 2 // Int type is inferred b = 3 // Compiler error! var x = 5 // Read-write Int x += 1 // Can be reassigned
9. 3. Null-safety val name: String = "John" val last: String? = "Wick" // ... println(name.length) println(last.length)
10. 3. Null-safety val name: String = "John" val last: String? = "Wick" // ... println(name.length) println(last?.length)
11. 3. Null-safety println(user?.name?.length)
12. 3. Null-safety println(user?.name?.length) == println( if (user != null && user.name != null) { user.name.length } else { null })
13. 4. Smart Cast open class Animal class Dog: Animal() { fun bark() } class Cat: Animal() { fun meow() }
14. 4. Smart Cast open class Animal class Dog: Animal() { fun bark() } class Cat: Animal() { fun meow() } val animal: Animal = fetch() when(animal) { is Dog -> animal.bark() is Cat -> animal.meow() }
15. 5. Higher-order functions (InputType) -> ReturnType “A higher-order function is a function that takes or returns another function”
16. 5. Higher-order functions ... fun parseName(parser: (String) -> Int): Int { // ... return parser(name) }
17. 5. Higher-order functions ... fun parseName(parser: (String) -> Int): Int { // ... return parser(name) }
18. 5. Higher-order functions fun parseName(parser: (String) -> Int): Int { // ... return parser(name) } val x: Int = parseName({ input: String -> input.length }) println(x)
19. 5. Higher-order functions fun parseName(parser: (String) -> Int): Int { // ... return parser(name) } val x: Int = parseName { input: String -> input.length } println(x)
20. 5. Higher-order functions fun parseName(parser: (String) -> Int): Int { // ... return parser(name) } val x = parseName { input -> input.length } println(x)
21. 4. Higher-order functions fun parseName(parser: (String) -> Int): Int { // ... return parser(name) } val x = parseName { it.length } println(x)
22. 5. Extension functions fun String.doubleLength(): Int { return this.length * 2 } // ... val x: Int = "John".doubleLength()
23. Bonus: kotlin-stdlib fun Iterable<T>.filter(predicate: (T) -> Boolean) { val out = ArrayList<T>() for (element in this) { if (predicate(element)) out.add(element) } return out }
24. Bonus: kotlin-stdlib val fruits = listOf("banana", "avocado", "apple", "kiwi") fruits .filter { it.startsWith("a") } .sortedBy { it } .map { it.toUpperCase() } .forEach { println(it) }
26. 0. Android Project Main screen, entry point App descriptor Main screen interface Compile and build instructions
27. An activity is the entry point for interacting with the user 1. Activities
28. 1. Activities An activity represents a single screen with a user interface
29. 1. Activities An Android app can have multiple entry points and activities
30. 1. Activities Any Android app can start another app’s activity
31. (Resources) Unique int ID for every resource cookie_oreo.png -> R.drawable.cookie_oreo activity_main.xml -> R.layout.activity_main Alternative resources for different device configurations res / values-en / strings.xml res / values-fr / strings.xml
32. 2. Layout
34. 2. Layout <?xml version="1.0" encoding="utf-8"?> <androidx.constraintlayout.widget.ConstraintLayout> <EditText android:id="@+id/msgText" android:layout_width="wrap_content" app:layout_constraintLeft_toLeftOf="parent" ... /> <Button android:id="@+id/sendBtn" android:text="Send" app:layout_constraintLeft_toRightOf="@id/msgText" ... /> </androidx.constraintlayout.widget.ConstraintLayout>
35. 2.1. Activity <-> Layout class MainActivity: AppCompatActivity() { override fun onCreate(...) { ... setContentView(R.layout.activity_main) val msgText = findViewById(R.id.msgText) val sendButton = findViewById(R.id.sendBtn) sendButton.setOnClickListener { // Do something when user clicks } } }
36. 3. Manifest App components ‍♀ Required user permissions Required hardware/software
37. 3. Manifest <?xml version="1.0" encoding="utf-8"?> <manifest ... > <uses-feature android:name="android.hardware.camera"/> <uses-permission android:name="android.permission.SEND_SMS"/> <application ...> <activity android:name="com.example.MainActivity" android:label="@string/main_title"/> <activity android:name="com.example.DetailsActivity" android:label="@string/details_title"/> </application> </manifest>
38. 3. Manifest <?xml version="1.0" encoding="utf-8"?> <manifest ... > <uses-feature android:name="android.hardware.camera"/> <uses-permission android:name="android.permission.SEND_SMS"/> <application ...> <activity android:name="com.example.MainActivity" android:label="@string/main_title"/> <activity android:name="com.example.DetailsActivity" android:label="@string/details_title"/> </application> </manifest> ♀
39. github.com/lgvalle/androidkotlinworkshop