Android Entwicklung mit Kotlin

Transcript

1. Android Entwicklung mit Kotlin Volkmar Vogel
2. • Entwickler: JetBrains • Version 1.0 am 15 Februar 2016 • Statisch typisierte Programmiersprache • Kompiliert zu Java 6 Bytecode
3. Syntax Crashkurs
4. int sum(int a, int b) {
 return a + b;
 }
5. fun sum(a: Int, b: Int): Int {
 return a + b
 }
6. fun sum(a: Int, b: Int) = a + b
7. final String immutable = "Hallo World”; 
 String mutable = "Hallo World";
8. val immutable = "Hallo World"
 var mutable = "Hallo World"
9. public class MyClass {
 
 private final String text;
 
 public MyClass(String text) {
 this.text = text;
 }
 
 public String getText() {
 return text;
 }
 }
10. class MyClass(val text: String)
11. public class DataClass {
 
 private final String nonNull;
 private final String nullable;
 
 public DataClass(@NonNull String nonNull,
 @Nullable String nullable) {
 
 this.nonNull = nonNull;
 this.nullable = nullable;
 }
 }
12. data class DataClass(val nonNull: String,
 val nullable: String?)
13. Null Safety
14. I call it my billion-dollar mistake. It was the invention of the null reference in 1965. […] This has led to innumerable errors, vulnerabilities, and system crashes, which have probably caused a billion dollars of pain and damage in the last forty years. Sir Tony Hoare (Quelle: Wikipedia)
16. var nonNull: String = "Hallo World"
 nonNull = null // kompiliert nicht
 
 var nullable: String? = "Hallo World"
 nullable = null
17. data class Person(val name: String?,
 val isMale: Boolean)
 
 val name = if (person.name == null) "Volkmar" else person.name
18. data class Person(val name: String?,
 val isMale: Boolean)
 
 val name = person.name ?: "Volkmar"
19. ?:)
20. data class Person(val name: String?,
 val isMale: Boolean)
21. data class Person(val name: String?,
 val isMale: Boolean)
 
 var personList: List<Person?>? = null
22. data class Person(val name: String?,
 val isMale: Boolean)
 
 var personList: List<Person?>? = null
23. data class Person(val name: String?,
 val isMale: Boolean)
 
 var personList: List<Person?>? = null
 personList
 ?.filterNotNull()
24. data class Person(val name: String?,
 val isMale: Boolean)
 
 var personList: List<Person?>? = null
 personList
 ?.filterNotNull()
 ?.filter { it.name != null }
25. data class Person(val name: String?,
 val isMale: Boolean)
 
 var personList: List<Person?>? = null
 personList
 ?.filterNotNull()
 ?.filter { it.name != null }
 ?.map {
 "${if (it.isMale) "Mr."
 else "Mrs."} ${it.name}"
 }
26. data class Person(val name: String?,
 val isMale: Boolean)
 
 var personList: List<Person?>? = null
 personList
 ?.filterNotNull()
 ?.filter { it.name != null }
 ?.map {
 "${if (it.isMale) "Mr."
 else "Mrs."} ${it.name}"
 }
 ?.forEach(::println)
27. Extension Functions
28. public class ContextUtils {
 public static void toast(Context ctx, String s) {
 Toast.makeText(ctx, s, Toast.LENGTH_SHORT).show();
 }
 }
29. fun Context.toast(s: String, 
 duration: Int = Toast.LENGTH_LONG) =
 Toast.makeText(this, s, duration).show()
30. fun Context.toast(s: String, 
 duration: Int = Toast.LENGTH_LONG) =
 Toast.makeText(this, s, duration).show()
32. Lambdas
33. view.setOnClickListener(new View.OnClickListener() {
 @Override
 public void onClick(final View v) {
 // do stuff
 }
 });
34. view.setOnClickListener {
 // do stuff
 }
35. val func1: () -> Unit = { /* do stuff */ }
 
 val func2: (Int) -> String = Int::toString
 
 val func3: (View) -> Unit = { it.visibility = View.GONE }
 view.setOnClickListener(func3)
36. //Collections.kt public inline fun <T> Iterable<T>.forEach(action: (T) -> Unit): Unit {
 for (element in this) action(element)
 } public inline fun <T, R> Iterable<T>.map(transform: (T) -> R): List<R> {
 return mapTo(ArrayList<R>(collectionSizeOrDefault(10)), transform)
 }
37. Demo!
38. Fragen?