Develop a weather app with Kotlin (AndroidMakers 17)

Develop a
weather app
with K

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Develop a weather app with
https://github.com/Ekito/2017-handson-kotlinAndroid
Grab your stuﬀ !
#androiddev #kotlin #AndroidMakersFr @ekito
WIFI: AndroidMakers / Makers2017

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Schedule
9:45 - Introduction

9:50 - Intro to Kotlin part 1

10:10 - Project presentation & setup

10:20 - Hands-on part 1 (55 minutes)

11:15 - Coﬀee break



12:40 - Final Part

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Practical notes
Grab your stuﬀ !

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@Baresse
Work @ ekito
Developer & Geek
Fullstack & Mobile
Laurent BARESSE
@arnogiu
Work @ ekito
Core & Gear Maker
Mobile & Cloud
Arnaud GIULIANI

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https://www.ekito.fr/careers
Join the team !

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Intro to
part 1

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« production ready »
15.02.2016

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Kotlin 1.1.1 @ 15.03.2017

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Yet another JVM
Language ?

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The new « Swift »
for Android ?

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Kotlin clearly considered
by the Java community !
https://spring.io/blog/2017/01/04/introducing-kotlin-support-in-
spring-framework-5-0
http://www.javamagazine.mozaicreader.com/
#&pageSet=5&page=0&contentItem=0 (March/April
2017)
https://www.thoughtworks.com/radar/languages-and-frameworks/kotlin

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- Conciseness & Smarter API
- Null Safety & Immutability protection
- Type Inference, Static Typing & Smart Casts
- Open programming styles
- Java Interop
Why
Kotlin ?

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What’s
Kotlin ?
- Fully open source (built by Jetbrains)
- Run on Java 6+
- Static typing & type inference
- Modern language features
- 1st grade tooling

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More About
Kotlin …
- String templates
- Properties
- Lambdas
- Data class
- Smart cast
- Null safety
- Lazy property
- Default values for function
parameters
- Extension Functions
- No more ;
- Single-expression
functions
- When expression
- let, apply, use, with
- Collections
- Android Extensions Plugin

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Compare with
Same conciseness and expressive code, but
Kotlin static typing and null-safety make a big
difference.
"Some people say Kotlin has 80% the power of
Scala, with 20% of the features" *  
"Kotlin is a software engineering language in
contrast to Scala which is a computing science
language." *
Swift and Kotlin are VERY similar. Swift is LLVM
based and has C interop while Kotlin is JVM based
and has Java interop.
* Quotes from Kotlin: The Ying and Yang of Programming Languages
@
sdeleuze

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is Kotlin Android friendly ?
https://github.com/SidneyXu/AndroidDemoIn4Languages
Method counts by Language

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KOTLIN is not just about writing
your app with lesser lines.
It’s all about writing
SAFER & BETTER APPS !

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20
Let’s Go !

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Typing & Inference
val a: Int = 1 
val b = 1 // `Int` type is inferred
var x = 5 // `Int` type is inferred 
x += 1
Inferred values
Mutable values
val : constant value - IMMUTABLE
var : variable value - MUTABLE
USE VAL AS MUCH AS POSSIBLE !

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Safety with Optionals
var stringA: String = "foo" 
stringA = null //Compilation error - stringA is a String (non optional) 
 
var stringB: String? = "bar" // stringB is an Optional String 
stringB = null //ok
Optional value

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// set length default value manually 
val length = if (stringB != null) stringB.length else -1 
//or with the Elvis operator 
val length = stringB?.length ?: -1
Default Value & Elvis Operator
val length = stringB.length // Compilation error - stringB can be null ! 
// use ? the safe call operator 
val length = stringB?.length //Value or null - length is type Int?
val length = stringB!!.length // Value or explicit throw NPE - length is type Int
Safe call with ?. or Explicit call with !!.

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Example
Working with optional values

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Example
Null check safety & Smart cast
Securing with default values

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Class
class User ( 
val userName: String, 
val ﬁrstName: String, 
val lastName: String, 
var location: Point? = null 
)
POJO +
- Getter
- Setter
- Constructors

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Data Class
data class User ( 
val userName: String, 
val ﬁrstName: String, 
val lastName: String, 
var location: Point? = null 
)
POJO +
- Getter
- Setter
- Constructors
- toString
- hashcode
- equals
- copy

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POJO ?
Kotlin
Java

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Properties
// readonly property 
val isEmpty: Boolean 
get() = this.size == 0
Properties can be declared in constructor or in class
You can also handle getter & setter
// customer getter & setter 
var stringRepresentation: String
set(value) { 
…
}
class ApiKey(var weatherKey: String, var geocodeKey: String){ 
var debug : Boolean = false 
}
* Late initialization, Lazy, Delegates …

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Example
data class User(val name: String = "", val age: Int = 0)
val jack = User(name = "Jack", age = 1) //no new keyword 
val anotherJack = jack.copy(age = 2)
Data Class usage
A simple GSon Class

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Object Class
// singleton 
object Resource { 
val name = "Name" 
}
class StringCalculator{
// class helper 
companion object{ 
val operators = arrayOf("+","-","x","/") 
} 
}
Singleton Class
Companion Object

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When
in ->
is ->
expression ->
when (s) { 
1 -> print("x == 1") 
2 -> print("x == 2") 
else -> { // Note the block 
print("x is neither 1 nor 2") 
} 
}
Flow Control (replace your old if blocks)
when (x) { 
in 1..10 -> print("x is in the range") 
in validNumbers -> print("x is valid") 
!in 10..20 -> print("x is outside the range") 
else -> print("none of the above") 
}
Pattern Matching
* can match with operators : in, as, is, range …

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Example
Android Page Adapter
Pattern Matching

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Collections
// immutable map 
val map = mapOf("a" to 1, "b" to 2, "c" to 3) 
for ((k, v) in map) { 
println("$k -> $v") 
}
 
map2["a"] = "my value" // direct map access with array style
// range 
for (i in 1..100) { //... }
// immutable list 
val list = listOf("a", "b", "c","aa") 
list.ﬁlter { it.startsWith("a") }
* collections operators : map, filter, take, flatMap, forEach, firstOrNull, last …

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Example
Kotlin Collection
Java 7 Collection

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InterOp Kotlin/Java
Java
Kotlin

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InterOp Java/Kotlin
object UserSingleton{ 
fun stringify(user : User) : String{ 
// … 
} 
}
fun WhatIsyourAge(user : User){ 
println("Your age is ${user.age}") 
}
data class User (val name: String, val age : Int){ 
companion object{ 
fun sayHello(user : User){
//… 
} 
} 
}
User u = new User("toto",42); 
User.Companion.sayHello(u);
UserUtilsKt.WhatIsyourAge(u);
UserSingleton.INSTANCE.stringify(u)

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Project presentation
& setup

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My Weather app

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Get the project

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Create your branch
https://github.com/Ekito/2017-handson-kotlinAndroid/blob/master/README.pdf

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Check your Kotlin plugin

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Adapt the config
In app & weathersdk modules:
- Android.BuildToolsVersion ~ 24.0.3
- com.android.support ~ 24.1.1
In root build.gradle:
- kotlin_version : 1.0.6+ (1.1.1)
- retroﬁt_version : 2.1.0+
- okhttp_version : 3.3.1+
In weathersdk module:
- rxjava : 1.2.0+ (2.0.5)
- rxandroid : 1.1.5 (2.0.1)
In root build.gradle:
- com.android.tools.build:gradle: 2.2.3
Do not upgrade to Gradle 2.3+ !

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MainApplication MainActivity
DailyForecastModel
DialogHelper
WeatherSDKUtil
WeatherSDK

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Hands-on
part 1

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9:45 - Introduction






12:40 - Final Part
Hands-on !

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9:45 - Introduction






12:40 - Final Part
Coffee Break !

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Intro to
part 2

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Sweet stuffs for

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Kotlin’s Android
Extensions
apply plugin: 'com.android.application'
apply plugin: ‘kotlin-android’
apply plugin: ‘kotlin-android-extensions’ // if use extensions
In your build.gradle

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Kotlin
Java

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Lambdas
val fab = findViewById(R.id.fab) as FloatingActionButton 
fab.setOnClickListener { view -> popLocationDialog(view) }
A lambda expression or an anonymous function is a “function literal”, i.e. a function that is
not declared, but passed immediately as an expression
- A lambda expression is always surrounded by curly braces
- Its parameters (if any) are declared before -> (parameter types may be omitted),
- The body goes after -> (when present).
myNumber.split("\n").flatMap { it.split(separator) } 
.map(Integer::parseInt) 
.map(::checkPositiveNumber) 
.filter { it <= 1000 } 
.sum()
* Method references are not surrounded by curly braces !

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Functions
fun reformat(str: String, 
normalizeCase: Boolean = true, 
upperCaseFirstLetter: Boolean = true, 
wordSeparator: Char = ' '): String { 
 
}
Named Parameters & default values
reformat(str, true, true, '_') // old way to call 
reformat(str, wordSeparator = '_') // using default values & named params

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Extensions Functions
Extension declaration
Usage

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Reactive
Programming

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Lamba expressions
Functional Programming
Reactive Streams
http://reactivex.io/documentation/operators.html
http://www.reactive-streams.org/
https://spring.io/blog/2016/06/07/notes-on-reactive-
programming-part-i-the-reactive-landscape

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Develop a weather app with Kotlin (AndroidMakers 17)

Develop a weather app with Kotlin (AndroidMakers 17)

Laurent BARESSE

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