android & kotlin - the code awakens #01

Android & KotlinThe code awakens #01

Omar MiatelloMember of GDG Milano (Italy)Android Developer @ Satispay

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What is Kotlin?

Statically typed programming language for the JVM, Android and the browser.(http://kotlinlang.org/)

Why Kotlin?

Concise: drastically reduce the amount of boilerplate code you need to write.

Safe: avoid entire classes of errors such as null pointer exceptions.

Interoperable: leverage existing frameworks and libraries of the JVM with 100% Java Interoperability.

and more... http://kotlinlang.org/docs/reference/comparison-to-java.html

Kotlin vs Java - Part 1Property

String templatesLambdas

Lazy properties

vspublic class MyKotlinClass { val a: Int = 1}

public class MyJavaClass { private final int a = 1;

public int getA() { return a; }}

#1 Kotlin - Properties: val, varhttp://kotlinlang.org/docs/reference/properties.html

public class MyKotlinClass { val a: Int = 1 var b: Int = 1}

public class MyJavaClass { private final int a = 1; private int b = 1;

public int getA() { return a; }

public int getB() { return b; }

public void setB(int b) { this.b = b; }}

#1 Kotlin - Properties: val, varhttp://kotlinlang.org/docs/reference/properties.html

vs

public class MyKotlinClass { val a: Int = 1 var b: Int = 1 val c = 1 var d = 1}

public class MyJavaClass { private final int a = 1; private int b = 1; private final int c = 1; private int d = 1;

public int getA() { return a; } public int getB() { return b; } public void setB(int b) { this.b = b; } public int getC() { return c; } public int getD() { return d; } public void setD(int d) { this.d = d; }}

#1 Kotlin - Properties: val, varhttp://kotlinlang.org/docs/reference/properties.html

vs

class MyKotlinClass { val name = "Omar" val surname = "Miatello"}

class MyJavaClass { final String getName() { return "Omar"; }

final String getSurname() { return "Miatello"; }}

#2 Kotlin - String templateshttp://kotlinlang.org/docs/reference/basic-syntax.html#using-string-templates

vs

class MyKotlinClass { val name = "Omar" val surname = "Miatello" val example = "My name is $name $surname"}

class MyJavaClass { final String getName() { return "Omar"; }

final String getSurname() { return "Miatello"; }

final String getExample() { return String.format("My name is %s %s", getName(), getSurname()); }}

#2 Kotlin - String templateshttp://kotlinlang.org/docs/reference/basic-syntax.html#using-string-templates

vs

class MyKotlinClass { val name = "Omar" val surname = "Miatello" val example = "My name is $name $surname"}

class MyJavaClass { final String getName() { return "Omar"; }

final String getSurname() { return "Miatello"; }

final String getExample() { return String.format("My name is %s %s", getName(), getSurname()); }}

#2 Kotlin - String templateshttp://kotlinlang.org/docs/reference/basic-syntax.html#using-string-templates

vs

class MyActivity : Activity() {

fun example() { val view = findViewById(R.id.button) view.setOnClickListener {

} }

}

class MyActivity extends Activity {

void example() { View view = findViewById(R.id.button); view.setOnClickListener(

); }

}

#3 Kotlin - Lambdashttp://kotlinlang.org/docs/reference/coding-conventions.html#lambdas

vs

class MyActivity : Activity() {

fun example() { val view = findViewById(R.id.button) view.setOnClickListener { Log.d("TAG", "Item clicked!") } }

}

class MyActivity extends Activity {

void example() { View view = findViewById(R.id.button); view.setOnClickListener( new View.OnClickListener() { @Override public void onClick(View v) { Log.d("TAG", "Item clicked!"); } } ); }

}

#3 Kotlin - Lambdashttp://kotlinlang.org/docs/reference/coding-conventions.html#lambdas

vs

class MyActivity : Activity() {

fun example() { val view = findViewById(R.id.button) view.setOnClickListener { Log.d("TAG", "Item clicked!") } }

}

class MyActivity extends Activity {

void example() { View view = findViewById(R.id.button); view.setOnClickListener( new View.OnClickListener() { @Override public void onClick(View v) { Log.d("TAG", "Item clicked!"); } } ); }

}

#3 Kotlin - Lambdashttp://kotlinlang.org/docs/reference/coding-conventions.html#lambdas

vs

class MyJavaClass { class MyItem { }

MyItem item;}

#4 Kotlin - Delegated Properties: lazy (as example)http://kotlinlang.org/docs/reference/delegated-properties.html

vs

class MyJavaClass { class MyItem { }

MyItem item;

final MyItem getItem() { if (item == null) { item = new MyItem(); } return item; }}

#4 Kotlin - Delegated Properties: lazy (as example)http://kotlinlang.org/docs/reference/delegated-properties.html

vs

class MyItem

class MyKotlinClass { val item by lazy { MyItem() }}

// Simplified: in Kotlin is synchronized

class MyJavaClass { class MyItem { }

MyItem item;

final MyItem getItem() { if (item == null) { item = new MyItem(); } return item; }}

#4 Kotlin - Delegated Properties: lazy (as example)http://kotlinlang.org/docs/reference/delegated-properties.html

vs

Install Kotlin in Android StudioPart 1 / 2

1. Open “Preferences”

Install Kotlin in Android Studio

1. Open “Preferences”

2. Choose “Plugins” and “Install JetBrains plugin…”

Install Kotlin in Android Studio

1. Open “Preferences”

2. Choose “Plugins” and “Install JetBrains plugin…”

3. Install “Kotlin” and “Kotlin Extensions For Android”

Install Kotlin in Android Studio

1. Open “Preferences”

2. Choose “Plugins” and “Install JetBrains plugin…”

3. Install “Kotlin” and “Kotlin Extensions For Android”

4. Restart Android Studio, and open (or create) a project

Install Kotlin in Android Studio

1. Open “Preferences”

2. Choose “Plugins” and “Install JetBrains plugin…”

3. Install “Kotlin” and “Kotlin Extensions For Android”

4. Restart Android Studio, and open (or create) a project

5. Create a new “Kotlin class”

Install Kotlin in Android Studio

Android ExampleFrom Java to Kotlin! (step1)

https://github.com/jacklt/KotlinExample/tree/java-version

dummy/HeroItem.javapublic class HeroItem { public final String id; public final String content; public final String details;

public HeroItem(String id, String content, String details) { this.id = id; this.content = content; this.details = details; }

@Override public String toString() { return content; }}

dummy/HeroItem.javapublic class HeroItem { public final String id; public final String content; public final String details;

public HeroItem(String id, String content, String details) { this.id = id; this.content = content; this.details = details; }

@Override public String toString() { return content; }}

“Convert Java File to Kotlin File”

CTRL + ALT + SHIFT + K(or CMD + ALT + SHIFT + K)

dummy/HeroItem.ktclass HeroItem(val id: String, val content: String, val details: String) { override fun toString(): String { return content }}

dummy/HeroItem.kt (optimized)

data class HeroItem(val id: String, val content: String, val details: String)

dummy/Items.kt (... a new hope)

data class HeroItem(val id: String, val content: String, val details: String)

data class VillanItem(val name: String, val power: String)

data class SpacecraftItem(val armaments: String, val defenses: String)

data class TinyItem(val name: String)

// ...

dummy/HeroAdapter.java (before HeroItem Conversion)

public class HeroAdapter extends RecyclerView.Adapter<HeroAdapter.ViewHolder> { // ... @Override public void onBindViewHolder(final ViewHolder holder, int position) { HeroItem item = mValues.get(position); holder.item = item; holder.idView.setText(item.id); holder.contentView.setText(item.content);

// ... }

// ...}

dummy/HeroAdapter.java (after HeroItem Conversion)

public class HeroAdapter extends RecyclerView.Adapter<HeroAdapter.ViewHolder> { // ... @Override public void onBindViewHolder(final ViewHolder holder, int position) { HeroItem item = mValues.get(position); holder.item = item; holder.idView.setText(item.getId()); holder.contentView.setText(item.getContent());

// ... }

// ...}

Install Kotlin in Android StudioPart 2 / 2

1. Open “Preferences”

2. Choose “Plugins” and “Install JetBrains plugin…”

3. Install “Kotlin” and “Kotlin Extensions For Android”

4. Restart Android Studio, and open (or create) a project

5. Create a new “Kotlin class”

6. Choose from menu “Tools” > “Kotlin” > “Configure Kotlin in Project”

Install Kotlin in Android Studio

1. Open “Preferences”

2. Choose “Plugins” and “Install JetBrains plugin…”

3. Install “Kotlin” and “Kotlin Extensions For Android”

4. Restart Android Studio, and open (or create) a project

5. Create a new “Kotlin class”

6. Choose from menu “Tools” > “Kotlin” > “Configure Kotlin in Project”

7. Ready for Kotlin! :)

dependencies { // other dependencies ... compile "org.jetbrains.kotlin:kotlin-stdlib:$kotlin_version"}buildscript { ext.kotlin_version = '1.0.0-beta-2423' repositories { mavenCentral() } dependencies { classpath "org.jetbrains.kotlin:kotlin-gradle-plugin:$kotlin_version" }}repositories { mavenCentral()}

Install Kotlin in Android Studio

Android ExampleFrom Java to Kotlin! (step2)

HeroAdapter

dummy/HeroAdapter.javapublic class HeroAdapter extends RecyclerView.Adapter<HeroAdapter.ViewHolder> {

private final List<HeroItem> mValues; private final HeroOnClickListener mListener;

public HeroAdapter(List<HeroItem> items, HeroOnClickListener listener) { mValues = items; mListener = listener; }

@Override public ViewHolder onCreateViewHolder(ViewGroup parent, int viewType) { View view = LayoutInflater.from(parent.getContext()).inflate(R.layout.item_hero, parent, false); return new ViewHolder(view); }

@Override public void onBindViewHolder(final ViewHolder holder, int position) { HeroItem item = mValues.get(position);

“Convert Java File to Kotlin File”

CTRL + ALT + SHIFT + K(or CMD + ALT + SHIFT + K)

dummy/HeroAdapter.kt (need manual fix)// ...inner class ViewHolder(view: View) : RecyclerView.ViewHolder(view) { val idView: TextView val contentView: TextView var item: HeroItem

init { idView = view.findViewById(R.id.id) as TextView contentView = view.findViewById(R.id.content) as TextView }}// ...

dummy/HeroAdapter.kt (fixed!)// ...inner class ViewHolder(view: View) : RecyclerView.ViewHolder(view) { val idView: TextView val contentView: TextView var item: HeroItem? = null

init { idView = view.findViewById(R.id.id) as TextView contentView = view.findViewById(R.id.content) as TextView }}// ...

dummy/HeroAdapter.kt (optimized)// OPTIMIZATION 1: In class constructorval mListener: HeroOnClickListener?// can be replaced withval mListener: Function1<HeroItem, Unit>?

// OPTIMIZATION 2: Method definitionoverride fun getItemCount(): Int { return mValues.size}// can be replaced withoverride fun getItemCount() = mValues.size

Android ExampleFrom Java to Kotlin! (step3)

MainActivitywith Kotlin Android Extension

build.gradle (add kotlin-android-extensions)

// ..

dependencies { classpath "org.jetbrains.kotlin:kotlin-gradle-plugin:$kotlin_version" classpath "org.jetbrains.kotlin:kotlin-android-extensions:$kotlin_version"}

// ..

build.gradle (add kotlin-android-extensions)

// ..

dependencies { classpath "org.jetbrains.kotlin:kotlin-gradle-plugin:$kotlin_version" classpath "org.jetbrains.kotlin:kotlin-android-extensions:$kotlin_version"}

// ..

MainActivity.javapublic class MainActivity extends AppCompatActivity {

private Toolbar toolbar; private FloatingActionButton fab; private RecyclerView recyclerView; private HeroAdapter adapter;

@Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.activity_main); toolbar = (Toolbar) findViewById(R.id.toolbar); setSupportActionBar(toolbar);

fab = (FloatingActionButton) findViewById(R.id.fab); fab.setOnClickListener(new View.OnClickListener() { @Override public void onClick(View view) { Snackbar.make(view, "Replace with your own action", Snackbar.LENGTH_LONG)

“Convert Java File to Kotlin File”

CTRL + ALT + SHIFT + K(or CMD + ALT + SHIFT + K)

MainActivity.kt (optimized, add import)import kotlinx.android.synthetic.activity_main.*

MainActivity.kt (optimized, use lazy for adapter)import kotlinx.android.synthetic.activity_main.*

class MainActivity : AppCompatActivity() { private val adapter by lazy { HeroAdapter(HeroDummyContent.ITEMS) { Snackbar.make(fab, "Tap on: " + it, Snackbar.LENGTH_SHORT).show() } }

MainActivity.kt (optimized, remove all unused property)import kotlinx.android.synthetic.activity_main.*

class MainActivity : AppCompatActivity() { private val adapter by lazy { HeroAdapter(HeroDummyContent.ITEMS) { Snackbar.make(fab, "Tap on: " + it, Snackbar.LENGTH_SHORT).show() } }

override fun onCreate(savedInstanceState: Bundle?) { super.onCreate(savedInstanceState) setContentView(R.layout.activity_main) setSupportActionBar(toolbar) fab.setOnClickListener { Snackbar.make(it, "...", Snackbar.LENGTH_LONG).setAction("Action", null).show() } recyclerView.layoutManager = LinearLayoutManager(this) recyclerView.adapter = adapter }}

Questions?Developers playground - #EX1 - Add properties to HeroItem: name, gender (String), power (Int)- Show item in list like: “$name (Power: $power)”- Choose (and keep in memory) hero “onClick”- Fight with second “onClick” (show a Snackbar)

Hint: Add in MainActivity “selectedHero” property (in Kotlin, or use field in Java)

Start with: https://github.com/jacklt/KotlinExample/tree/java-version or https://github.com/jacklt/KotlinExample/tree/kotlin-version

Solution: https://github.com/jacklt/KotlinExample/tree/ex1

THANKS!Omar Miatello, Member of GDG Milano (Italy)

Android Developer @ Satispay