Kotlin for Android Developers

Discover some of the most interesting Kotlin features that will make Android development much easier.

Slides from talk at CodeWeek Cáceres (October 2015)

Transcript

1. Kotlin for Android Developers Antonio Leiva @lime_cl
2. http://plex.tv
3. http://antonioleiva.com
5. Kotlin features
6. What is Kotlin? • JVM based • Object-oriented functional language • Created by JetBrains (IntelliJ, Android Studio) • Simple,lightweight, interoperable
7. Kotlin features Title Text Null safety
8. Null safety Artist artist = null;
 artist.print(); JAVA Null Pointer Exception
9. Null safety KOTLIN var artist: Artist? = null
 artist.print() var artist: Artist? = null
 artist?.print() won´t compile will do nothing if (artist != null) {
 artist.print()
 } Smart cast var artist: Artist? = null
 artist!!.print() will crash
10. Kotlin features Title Text Properties
11. Properties private String field = “”;
 
 public String getField() {
 return field;
 }
 
 public void setField(String field) {
 this.field = field;
 } JAVA
12. Properties var property: String = "" KOTLIN
13. Properties var property: String = ""
 get(){
 return "property is $field"
 }
 set(value: String){
 if (value != "")
 field = value
 }
14. Kotlin features Title Text Data Classes
15. Data Classes public class Artist {
 private long id;
 private String name;
 private String url;
 private String mbid;
 
 public long getId() {
 return id;
 }
 
 public void setId(long id) {
 this.id = id;
 }
 
 public String getName() {
 return name;
 }
 
 public void setName(String name) {
 this.name = name;
 }
 
 public String getUrl() {
 return url;
 }
 
 public void setUrl(String url) {
 this.url = url;
 }
 
 public String getMbid() {
 return mbid;
 }
 
 public void setMbid(String mbid) {
 this.mbid = mbid;
 }
 
 @Override public String toString() {
 return "Artist{" +
 "id=" + id +
 ", name='" + name + '\'' +
 ", url='" + url + '\'' +
 ", mbid='" + mbid + '\'' +
 '}';
 }
 }
 JAVA
16. Data Classes data class Artist(
 var id: Long,
 var name: String,
 var url: String,
 var mbid: String) KOTLIN
17. Kotlin is functional
18. Kotlin is functional (kind of)
19. Kotlin is functional Lambdas
20. Lambdas function: (T) -> R
21. Lambdas public interface Callback<T> {
 void invoke(T result);
 }
 
 public void asyncOperation(int value, Callback<Boolean> callback){
 ...
 callback.invoke(true);
 } JAVA asyncOperation(5, new Callback<Boolean>() {
 @Override public void invoke(Boolean result) {
 System.out.println("Result: " + result);
 }
 });
22. Lambdas fun asyncOperation(value: Int, callback: (Boolean) -> Unit) {
 ...
 callback(true)
 } asyncOperation(5) { result ->
 println("result: $result")
 }
23. Lambdas fun asyncOperation(value: Int, callback: (Boolean) -> Unit) {
 ...
 callback(true)
 } asyncOperation(5) { result ->
 println("result: $result")
 } asyncOperation(5) { println("result: $it") }
24. Lambdas asyncOperation(5) { println("result: $it") } asyncOperation(5, new Callback<Boolean>() {
 @Override public void invoke(Boolean result) {
 System.out.println("Result: " + result);
 }
 });
25. Kotlin is functional Collections
26. Collections • Iterable • Collection • List • Set • Map filter sort map zip dropWhile first firstOrNull last lastOrNull fold …
27. Collections parsedContacts .filter { it.name != null && it.image != null }
 .sortedBy { it.name }
 .map { Contact(it.id, it.name!!, it.image!!) }
28. Kotlin is functional Extending language
29. Extending language inline fun supportsLollipop(code:() -> Unit) {
 if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.LOLLIPOP){
 code.invoke()
 }
 } supportsLollipop {
 getWindow().setStatusBarColor(Color.BLACK)
 }
30. More awesome features!
31. More awesome features! Extension functions
32. Extension functions fun Context.toast(message: CharSequence){
 Toast.makeText(this, message, duration).show()
 }
33. Extension functions fun Context.toast(message: CharSequence){
 Toast.makeText(this, message, duration).show()
 } context.toast("I'm a context")
 activity.toast("I'm an activity")
 service.toast("I'm a service")
34. Extension functions fun Long.toDateString(dateFormat: Int = DateFormat.MEDIUM): String {
 val df = DateFormat.getDateInstance(dateFormat, Locale.getDefault())
 return df.format(this)
 }
35. More awesome features! Default arguments
36. Default arguments fun Long.toDateString(dateFormat: Int = DateFormat.MEDIUM): String {
 val df = DateFormat.getDateInstance(dateFormat, Locale.getDefault())
 return df.format(this)
 }
37. Default arguments fun Long.toDateString(dateFormat: Int = DateFormat.MEDIUM): String {
 val df = DateFormat.getDateInstance(dateFormat, Locale.getDefault())
 return df.format(this)
 } dateLong.toDateString()
 dateLong.toDateString(DateFormat.FULL)
38. Default arguments fun Activity.toast(message: CharSequence, duration: Int = Toast.LENGTH_SHORT){
 Toast.makeText(this, message, duration).show()
 } toast(“Short Toast!!”) toast("Long Toast!!", Toast.LENGTH_LONG)
39. More awesome features! Interfaces
40. Interfaces • Can contain code (but not state) interface ToolbarManager {
 
 val toolbar: Toolbar
 
 fun initToolbar() {
 toolbar.inflateMenu(R.menu.menu_main)
 toolbar.setOnMenuItemClickListener {
 when (it.itemId) {
 R.id.action_settings -> App.instance.toast("Settings")
 else -> App.instance.toast("Unknown option")
 }
 true
 }
 }
 }
41. Interfaces class MainActivity : AppCompatActivity(), ToolbarManager {
 
 override val toolbar by lazy { find<Toolbar>(R.id.toolbar) }
 
 override fun onCreate(savedInstanceState: Bundle?) {
 super.onCreate(savedInstanceState)
 setContentView(R.layout.activity_main)
 initToolbar()
 ...
 }
 }

42. More awesome features! Property delegation
43. Property delegation val toolbar by lazy { find<Toolbar>(R.id.toolbar) } • Lazy var p by Delegates.observable("") { d, old, new -> db.saveChanges(this, new) } • Observable • Not Null • Vetoable • Values from map • Custom
44. More awesome features! Flow control
45. Flow control • If • When • For • While
46. Flow control • If val z = if (condition) x else y
47. Flow control • When val cost = when(x) {
 in 1..10 -> "cheap"
 in 10..100 -> "regular"
 in 100..1000 -> "expensive"
 in specialValues -> "special value!"
 else -> "not rated"
 }
48. Flow control • When val res = when {
 x in 1..10 -> "cheap"
 s.contains("hello") -> "it's a welcome!"
 v is ViewGroup -> "child count: ${v.getChildCount()}"
 else -> ""
 }
49. More awesome features! Title Text Interoperability
50. Interoperability Palette.generateAsync(bitmap, new Palette.PaletteAsyncListener() {
 @Override public void onGenerated(Palette palette) {
 …
 }
 }); JAVA
51. Interoperability Palette.generateAsync(bitmap, new Palette.PaletteAsyncListener() {
 @Override public void onGenerated(Palette palette) {
 …
 }
 }); Palette.generateAsync(bitmap) { palette ->
 …
 } JAVA KOTLIN
52. Interoperability view.setOnClickListener(object : View.OnClickListener{
 override fun onClick(v: View) {
 toast("Click")
 }
 }) Regular anonymous class (similar to Java)
53. Interoperability If interface only has a function, substitute by function view.setOnClickListener({ view ->
 toast("Click")
 })
54. Interoperability view.setOnClickListener({
 toast("Click")
 }) If interface only has a function, substitute by function view.setOnClickListener({ view ->
 toast("Click")
 })
55. Interoperability view.setOnClickListener() {
 toast("Click")
 } If last parameter is a function, can go out of parenthesis
56. Interoperability view.setOnClickListener() {
 toast("Click")
 } If last parameter is a function, can go out of parenthesis view.setOnClickListener {
 toast("Click")
 }
57. Interoperability view.setOnClickListener(object : View.OnClickListener{
 override fun onClick(v: View) {
 toast("Click")
 }
 }) view.setOnClickListener { toast("Click") }
58. Interoperability Getter (+Setter) -> Property supportActionBar.title = title
 textView.text = title contactsList.adapter = ContactsAdapter()
59. Kotlin Android Extensions
60. Kotlin Android Extensions Direct access to XML views using its id as property name main.xml <FrameLayout
 xmlns:android="..."
 android:id="@+id/frameLayout"
 android:orientation="vertical"
 android:layout_width="match_parent"
 android:layout_height="match_parent">
 
 <TextView
 android:id="@+id/welcomeText"
 android:layout_width="wrap_content"
 android:layout_height="wrap_content"/>
 
 </FrameLayout>
61. Kotlin Android Extensions Import synthetic properties import kotlinx.android.synthetic.main.* Use the properties override fun onCreate(savedInstanceState: Bundle?) {
 super<BaseActivity>.onCreate(savedInstanceState) setContentView(R.id.main)
 frameLayout.setVisibility(View.VISIBLE)
 welcomeText.setText("I´m a welcome text!!")
 }
62. Anko
63. Anko UI declaration DSL
64. UI declaration DSL verticalLayout {
 val name = editText()
 button("Say Hello") {
 onClick { toast("Hello, ${name.text}!") }
 }
 }
65. Anko Useful extensions
66. Useful extensions startActivity<DetailActivity>("id" to res.id, "name" to res.name) Start an activity Access to system services context.layoutInflater context.notificationManager
 context.sensorManager
 context.vibrator
67. Useful extensions Toasts and Alert dialogs toast(R.string.message)
 longToast("Wow, such a duration")
 
 alert("Yes /no Alert") {
 positiveButton("Yes") { submit() }
 negativeButton("No") {}
 }.show()
68. Anko Easy asynchrony
69. Easy asynchrony async {
 val result = longRequest()
 uiThread { bindForecast(result) }
 }
70. Anko SQLite helpers
71. SQLite helpers ManagedSQLiteOpenHelper dbHelper.use {
 select("TABLE_NAME").where("_id = {id}", "id" to 20)
 } db.createTable("TABLE_NAME", true,
 "_id" to INTEGER + PRIMARY_KEY,
 "name" to TEXT) parseList / parseOpt / classParser…
72. Conclusion
73. Conclusion • Lightweight, simple and powerful • Simplifies Android Development • Version 1.0 -> soon!
74. http://antonioleiva.com/book/ Kotlin for Android Developers • Create App from scratch • Step by step • Complete Kotlin coverage • Updated to latest version
75. http://antonioleiva.com/book/ ?