Android Development with Kotlin (AndroidKW #001)

Jake Wharton
Android Development
with Kotlin

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Why do we need Kotlin?

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• Stuck on Java 6(.5)ish

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• No javax.time

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• No javax.time
• No streams

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• No javax.time
• No streams
• No lambdas, method refs, non-capturing anon class

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• No javax.time
• No streams
• No try-with-resources

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• No javax.time Use ThreeTenBP / ThreeTenABP
• No streams

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• No streams Use backport or RxJava

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• No lambdas, method refs, non-capturing anon class Use Retrolambda

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• No lambdas, method refs, non-capturing anon class Use Retrolambda
• No try-with-resources minSdkVersion=19 or Retrolambda

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• Java language restrictions and problems

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• Inability to add methods to platform types

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• Inability to add methods to platform types ("Util" hell)

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• Nullability problems

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• Mutability problems

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• Mutability problems
• General verbosity of common idioms

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• Android API design problems

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• Inheritance party

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• Nullability everywhere

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• Nullability everywhere
• Ceremony of APIs

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Kotlin
Statically typed programming language
for the JVM, Android, and the browser
100% interoperable with Java™

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Syntax Crash Course

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Syntax Crash Course
fun sum(a: Int, b: Int): Int { 
return a + b 
}

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Syntax Crash Course
fun sum(a: Int, b: Int): Int { 
return a + b 
}X

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Syntax Crash Course
fun sum(a: Int, b: Int) = a + b

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Syntax Crash Course
fun main(args: Array) { 
println("Args: $args") 
}

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Syntax Crash Course
fun main(args: Array) { 
println("Args: $args") 
}X

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Syntax Crash Course
val name = "Jake" 
val people: List = ArrayList()

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Extension Functions

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Extension Functions
static boolean isTuesday(Date date) { 
return date.getDay() == 2; 
}

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Extension Functions
}
boolean tuesday = DateUtils.isTuesday(date);

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Extension Functions
fun Date.isTuesday(): Boolean { 
return getDay() == 2 
}X

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Extension Functions
return getDay() == 2 
}X
val tuesday = date.isTuesday()

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Extension Functions
return day == 2 
}X

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Extension Functions
fun Date.isTuesday() = day == 2

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Extension Functions
// com/example/util/DateExtensions.kt
// com/example/TuesdayActivity.kt

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Extension Functions
// com/example/TuesdayActivity.kt
import com.example.util.isTuesday

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Extension Functions
final static isTuesday(Ljava/util/Date;)Z
L0
ALOAD 0
INVOKEVIRTUAL java/util/Date.getDay ()I
ICONST_2
IF_ICMPNE L1
ICONST_1
GOTO L2
L1
ICONST_0
L2
IRETURN

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Extension Functions
}X

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Extension Functions
// com/example/util/DateExtensionsKt.java
}X

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Extension Functions
@file:JvmName("DateUtils")
// com/example/util/DateExtensionsKt.java
}X

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Extension Functions
@file:JvmName("DateUtils")
// com/example/util/DateUtils.java
}X

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Extension Functions
fun Date.getDay() = 2

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Extension Functions
fun View.isAttachedToWindow() =
if (Build.VERSION.SDK_INT < 19)
ViewCompat.isAttachedToWindow(this)
else
super.isAttachedToWindow()

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Extension Functions
fun View.isAttachedToWindowCompat() =
if (Build.VERSION.SDK_INT < 19)
ViewCompat.isAttachedToWindow(this)
else
isAttachedToWindow()

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Extension Functions
String firstName1=2cursor.getString(
cursor.getColumnIndexOrThrow("first_name"));

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Extension Functions
String firstName1= null; 
int firstNameColumn = cursor.getColumnIndexOrThrow("first_name"); 
if (!cursor.isNull(firstNameColumn)) { 
firstName3=2cursor.getString(firstNameColumn); 
}

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Extension Functions
String firstName1= null; 
int firstNameColumn = cursor.getColumnIndexOrThrow("first_name"); 
if (!cursor.isNull(firstNameColumn)) { 
firstName3=2cursor.getString(firstNameColumn); 
}
fun Cursor.getStringOrNull(columnName: String): String? { 
val index = getColumnIndexOrThrow(columnName) 
return if (isNull(index)) null else getString(index) 
}X 
fun Cursor.getString(columnName: String): String =
getStringOrNull(columnName)!!

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Extension Functions
}X 

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Extension Functions
}X 
val firstName = cursor.getStringOrNull("first_name")

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Extension Functions
}X 
val firstName: String? = cursor.getStringOrNull("first_name")

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Extension Functions
}X 
if (firstName != null) {
firstNameView.setText(firstName)
}X

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Extension Functions
}X 
if (firstName != null) {
firstNameView.setText(firstName) // firstName not String?, now String
}X

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Extension Functions
}X 
firstNameView.setText(firstName ?: "Jake")

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Extension Functions
}X 
val firstName = cursor.getString("first_name")

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Extension Functions
}X 
val firstName: String = cursor.getString("first_name")

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Extension Functions
}X 
val firstName: String = cursor.getString("first_name")
firstNameView.setText(firstName)

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Function Expressions

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{ it.toString() }

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{ x, y -> x + y }
{ it.toString() }

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{ x, y -> x + y }
{ x: Int, y: Int -> x + y }
{ it.toString() }
{ x, y -> x + y }
{ x: Int, y: Int -> x + y }

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{ x, y -> x + y }
{ x: Int, y: Int -> x + y }
val sum = { x: Int, y: Int -> x + y }
val sum: (Int, Int) -> Int = { x, y -> x + y }
{ it.toString() }

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{ !it.isEmpty() }
{ it.length() > 4 }
{ it.matches("\\d{4}") }
{ luhnCheck(it) }

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val notEmpty: (String) -> Boolean = { !it.isEmpty() }
val atLeastFour: (String) -> Boolean = { it.length() > 4 }
val fourDigits: (String) -> Boolean = { it.matches("\\d{4}") }
val validCreditCard: (String) -> Boolean = { luhnCheck(it) }

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Higher-Order Functions

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fun List.filter(predicate: (T) -> Boolean): List {
// ... 
}X

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fun List.filter(predicate: (T) -> Boolean): List { 
val newList = ArrayList()
// ... 
return newList 
}X

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val newList = ArrayList() 
for (item in this) {
// ... 
}Y 
return newList 
}X

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for (item in this) { 
if (predicate(item)) {
// ... 
}Z 
}Y 
return newList 
}X

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if (predicate(item)) { 
newList.add(item) 
}Z 
}Y 
return newList 
}X

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if (predicate(item)) { 
newList.add(item) 
} 
} 
return newList 
}
val names = listOf("Jake", "Jesse", "Matt", "Alec") 
val jakes = names.filter { it == "Jake" } 

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data class Lock(private val obj: T) { 
public fun acquire(func: (T) -> Unit) { 
synchronized (obj) { 
func(obj) 
}X 
}X 
}X

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func(obj) 
} 
} 
}

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func(obj) 
} 
} 
}
val readerLock = Lock(JsonReader(stream))

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func(obj) 
} 
} 
}
val readerLock = Lock(JsonReader(stream)) 
 
// Later 
readerLock.acquire {  
println(it.readString()) 
}

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firstName.validateWith(notEmpty)
lastName.validateWith(notEmpty)
username.validateWith(atLeastFour)
pin.validateWith(fourDigits)
creditCard.validateWith(validCreditCard)
{ !it.isEmpty() }

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firstName.validateWith { !it.isEmpty() }
lastName.validateWith { !it.isEmpty() }
username.validateWith { it.length() > 4 }
pin.validateWith { it.matches("\\d{4}") }
creditCard.validateWith { luhnCheck(it) }

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firstName.validateWith(notEmpty)
lastName.validateWith(notEmpty)
username.validateWith { it.length() > 4 }
pin.validateWith { it.matches("\\d{4}") }
creditCard.validateWith { luhnCheck(it) }
{ !it.isEmpty() }

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Extension Function Expressions

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• Extension Functions — Functions added to a type without modifying
the original.

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the original.
• Function Expressions — Undeclared function bodies used an as
expression (i.e., as data).

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the original.
• Function Expressions — Undeclared function bodies used an as
expression (i.e., as data).
• Higher-Order Functions: A function which takes a function or returns
a function.

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db.beginTransaction(); 
try { 
db.delete("users", "first_name = ?", new String[] { "Jake" }); 
} finally { 
db.endTransaction(); 
}X

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try { 
db.delete("users", "first_name = ?", new String[] { "Jake" }); 
db.setTransactionSuccessful(); 
} finally { 
}X

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fun SQLiteDatabase.inTransaction(func: () -> Unit) { 
beginTransaction() 
try { 
func() 
setTransactionSuccessful() 
} finally { 
endTransaction() 
} 
}

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try { 
func( 
} finally { 
endTransaction() 
}Y 
}X
db.inTransaction {  
}X
)

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try { 
func( 
} finally { 
endTransaction() 
}Y 
}X
db.delete("users", "first_name = ?", arrayOf("Jake")) 
}X
)

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fun SQLiteDatabase.inTransaction(func: (SQLiteDatabase) -> Unit) { 
try { 
func( 
} finally { 
endTransaction() 
}Y 
}X
}X
)

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try { 
func(this 
} finally { 
endTransaction() 
}Y 
}X
}X
)

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try { 
func(this 
} finally { 
endTransaction() 
}Y 
}X
it.delete("users", "first_name = ?", arrayOf("Jake")) 
}X
)

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fun SQLiteDatabase.inTransaction(func: SQLiteDatabase.() -> Unit) { 
try { 
func(this 
} finally { 
endTransaction() 
}Y 
}X
}X
)

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try { 
this.func( 
} finally { 
endTransaction() 
}Y 
}X
}X
)

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try { 
func( 
} finally { 
endTransaction() 
}Y 
}X
}X
)

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try { 
func() 
} finally { 
endTransaction() 
}Y 
}X
delete("users", "first_name = ?", arrayOf("Jake")) 
}X

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}X

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NEW MyClassKt$deleteUsers$1
DUP
ALOAD 2
INVOKESPECIAL MyClassKt$deleteUsers$1. (Ljava/lang/String;)V
CHECKCAST kotlin/jvm/functions/Function1
INVOKESTATIC DbExtensionsKt.inTransaction
(Landroid/database/sqlite/SQLiteDatabase;Lkotlin/jvm/functions/Function1;)V
}X

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DbExtensions.inTransaction(db, new Function1() { 
@Override public Unit invoke(SQLiteDatabase db) { 
db.delete("users", "first_name = ?", new String[] { "Jake "}); 
return null; 
} 
});
}X

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try { 
func() 
} finally { 
endTransaction() 
}Y 
}X

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inline fun SQLiteDatabase.inTransaction(func: SQLiteDatabase.() -> Unit) { 
try { 
func() 
} finally { 
endTransaction() 
}Y 
}X

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L6
ALOAD 2
INVOKEVIRTUAL com/example/SQLiteDatabase.beginTransaction ()V
L0
NOP
L9
ALOAD 2
CHECKCAST com/example/SQLiteDatabase
ASTORE 3
L10
ALOAD 3
LDC "users"
LDC "first_name = ?"
ICONST_1
ANEWARRAY java/lang/String
DUP
ICONST_0
LDC "Jake"
AASTORE
CHECKCAST [Ljava/lang/String;
INVOKEVIRTUAL com/example/SQLiteDatabase.delete (Ljava/lang/String;Ljava/lang/String;[Ljava/lang/String;)V
L11
L12
GETSTATIC kotlin/Unit.INSTANCE : Lkotlin/Unit;
POP
L13
ALOAD 2
INVOKEVIRTUAL com/example/SQLiteDatabase.setTransactionSuccessful ()V
L1
ALOAD 2
INVOKEVIRTUAL com/example/SQLiteDatabase.endTransaction ()V
L14
GOTO L15
L2
ASTORE 3
L3
ALOAD 2
INVOKEVIRTUAL com/example/SQLiteDatabase.endTransaction ()V

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try { 
} finally { 
}X

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try { 
} finally { 
}X
}X
+
inline fun
=

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inline fun SharedPreferences.edit(func: SharedPreferences.Editor.() -> Unit) { 
val editor = edit() 
editor.func() 
editor.apply() 
}

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editor.func() 
editor.apply() 
}X
preferences.edit {  
putString("foo", "bar") 
putString("fizz", "buzz") 
remove("username") 
}X

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editor.func() 
editor.apply() 
}X
 
fun SharedPreferences.Editor.set(pair: Pair) = 
putString(pair.first, pair.second)
preferences.edit {  
putString("foo", "bar") 
putString("fizz", "buzz") 
}X

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editor.func() 
editor.apply() 
}X
 
fun SharedPreferences.Editor.set(pair: Pair) = 
putString(pair.first, pair.second)
preferences.edit { 
set("foo" to "bar") 
set("fizz" to "buzz") 
}X
 
 
 
 
 
 
 
putString 
putString

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inline fun notification(context: Context,
func: Notification.Builder.() -> Unit): Notification { 
val builder = Notification.Builder(context) 
builder.func() 
return builder.build() 
}

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inline fun notification(context: Context,
func: Notification.Builder.() -> Unit): Notification { 
val builder = Notification.Builder(context) 
builder.func() 
return builder.build() 
}
val n = notification(context) { 
setContentTitle("Hi") 
setSubText("Hello") 
}

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verticalLayout { 
padding = dip(30) 
editText { 
hint = "Name" 
textSize = 24f 
} 
editText { 
hint = "Password" 
textSize = 24f 
} 
button("Login") { 
textSize = 26f 
} 
}

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Resources

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Resources
• Website and documentation 
https://kotlinlang.org/

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Resources
• Online IDE 
http://try.kotlinlang.org/

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Resources
• Online IDE 
http://try.kotlinlang.org/
• Kotlin Koans 
http://try.kotlinlang.org/koans

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jakewharton
jakewharton
jakewharton
twitter.com/
google.com/+
.com
Android Development
with Kotlin

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Android Development with Kotlin (AndroidKW #001)

Android Development with Kotlin (AndroidKW #001)

Jake Wharton
PRO

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Transcript

Android Development with Kotlin (AndroidKW #001)

Android Development with Kotlin (AndroidKW #001)

Jake Wharton PRO

More Decks by Jake Wharton

Other Decks in Programming

Featured

Transcript

Jake Wharton
PRO