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https://github.com/ravidsrk/blrkotlin2018
Slides and references used for "Pragmatic Kotlin for Android Developers" talk at #BlrKotlin2018
https://github.com/ravidsrk/blrkotlin2018
android kotlin
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Slides and references used for "Pragmatic Kotlin for Android Developers" talk at #BlrKotlin2018
- Host: GitHub
- URL: https://github.com/ravidsrk/blrkotlin2018
- Owner: ravidsrk
- License: mit
- Created: 2018-01-05T12:00:42.000Z (almost 7 years ago)
- Default Branch: master
- Last Pushed: 2018-01-06T03:10:08.000Z (almost 7 years ago)
- Last Synced: 2024-04-14T20:02:32.575Z (7 months ago)
- Topics: android, kotlin
- Language: Kotlin
- Size: 8.84 MB
- Stars: 9
- Watchers: 2
- Forks: 0
- Open Issues: 0
-
Metadata Files:
- Readme: README.md
- License: LICENSE
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README
# Pragmatic **Kotlin :heart:**
##### Practical Tips to migrate your Android App to Kotlin
###### By Ravindra Kumar [@ravidsrk](https://twitter.com/ravidsrk)
---
# About **Me**
* Ravindra Kumar **[@ravidsrk](https://ravidsrk.com/)**
* Android Developer **[@Fueled](https://fueled.com/ravindra-kumar/)**
* Speaker at **Droidcon In, Jsfoo, TiConf, Devfest**
* Creator of **[AndroidStarters.com](http://androidstarters.com/)** and **[KotlinExtensions.com](http://kotlinextensions.com/)**
* Open source contributor **[@ravidsrk](https://github.com/ravidsrk)**
* Author of [**Android Testing Guide**](https://leanpub.com/android-testing)
---
# Agenda
* Steps to Convert
* Common converter Issues
* Takeaways
* Eliminate all `!!` from your Kotlin code
* Kotlin Extensions
* Kotlin Android Extensions
---
# Steps to **Convert**
Once you learn basics syntax of **Kotlin**
1. Convert files, one by one, via **"⌥⇧⌘K",** make sure tests still pass
---
# Steps to **Convert**
Once you learn basics syntax of **Kotlin**
1. Convert files, one by one, via **"⌥⇧⌘K",** make sure tests still pass
2. Go over the Kotlin files and make them more [idiomatic](https://blog.philipphauer.de/idiomatic-kotlin-best-practices/).
---
# Steps to **Convert**
Once you learn basics syntax of **Kotlin**
1. Convert files, one by one, via **"⌥⇧⌘K",** make sure tests still pass
2. Go over the Kotlin files and make them more [idiomatic](https://blog.philipphauer.de/idiomatic-kotlin-best-practices/).
3. Repeat step 2 until you convert all the files.
---
# Steps to **Convert**
Once you learn basics syntax of **Kotlin**
1. Convert files, one by one, via **"⌥⇧⌘K",** make sure tests still pass
2. Go over the Kotlin files and make them more [idiomatic](https://blog.philipphauer.de/idiomatic-kotlin-best-practices/).
3. Repeat step 2 until you convert all the files.
4. Ship it.
---
# Common Converter **Issues**
* **TypeCasting** for the sake of Interoperability.
* **Companion** will add extra layer.
* If java method starting with **getFoo()**, converter looks for property with the name **foo**.
* Generics are hard to get it right on the first go.
* No argument captor.
* **git diff** If two developers are working on same java file and one guy converts it to Kotlin, it will be rework.
---
# **TypeCasting** for the sake of **Interoperability**
Here is the Java class:
```java
public class DemoFragment extends BaseFragment implements DemoView {
@Override
public void displayMessageFromApi(String apiMessage) {
...
}
}
```
---
# **TypeCasting** for the sake of **Interoperability**
```kotlin
// Kotlin class
class DemoResponse {
@SerializedName("message") var message: String? = null
}
```
---
# **TypeCasting** for the sake of **Interoperability**
```kotlin
// Kotlin class
class DemoResponse {
@SerializedName("message") var message: String? = null
}
// Typecasting to String
mainView?.displayMessageFromApi(demoResponse.message)
```
---
# **TypeCasting** for the sake of **Interoperability**
```kotlin
// Kotlin class
class DemoResponse {
@SerializedName("message") var message: String? = null
}
// Typecasting to String
mainView?.displayMessageFromApi(demoResponse.message) // Compiler Error
```
---
# **TypeCasting** for the sake of **Interoperability**
```kotlin
// Kotlin class
class DemoResponse {
@SerializedName("message") var message: String? = null
}
// Typecasting to String
mainView?.displayMessageFromApi(demoResponse.message as String)
```
---
# **Companion** will add extra layer
Here is Java class:
```java
public class DetailActivity extends BaseActivity implements DetailMvpView{
public static final String EXTRA_POKEMON_NAME = "EXTRA_POKEMON_NAME";
public static Intent getStartIntent(Context context, String pokemonName) {
Intent intent = new Intent(context, DetailActivity.class);
intent.putExtra(EXTRA_POKEMON_NAME, pokemonName);
return intent;
}
}
```
---
# **Companion** will add extra layer
Converted Kotlin class:
```kotlin
class DetailActivity : BaseActivity(), DetailMvpView {
companion object {
val EXTRA_POKEMON_NAME = "EXTRA_POKEMON_NAME"
fun getStartIntent(context: Context, pokemonName: String): Intent {
val intent = Intent(context, DetailActivity::class.java)
intent.putExtra(EXTRA_POKEMON_NAME, pokemonName)
return intent
}
}
}
```
---
# **Companion** will add extra layer
```java
public class MainActivity extends BaseActivity implements MainMvpView {
private void pokemonClicked(Pokemon pokemon) {
startActivity(DetailActivity.Companion.getStartIntent(this, pokemon))
}
}
```
---
# Add `@JvmStatic`
Converted Kotlin class:
```kotlin
class DetailActivity : BaseActivity(), DetailMvpView {
companion object {
val EXTRA_POKEMON_NAME = "EXTRA_POKEMON_NAME"
@JvmStatic
fun getStartIntent(context: Context, pokemonName: String): Intent {
val intent = Intent(context, DetailActivity::class.java)
intent.putExtra(EXTRA_POKEMON_NAME, pokemonName)
return intent
}
}
}
```
---
# Add `@JvmStatic`
```java
public class MainActivity extends BaseActivity implements MainMvpView {
private void pokemonClicked(Pokemon pokemon) {
startActivity(DetailActivity.getStartIntent(this, pokemon))
}
}
```
---
# Add `@JvmStatic`
```java
public class MainActivity extends BaseActivity implements MainMvpView {
private void pokemonClicked(Pokemon pokemon) {
startActivity(DetailActivity.getStartIntent(this, pokemon))
}
}
```
> **Remember:** *you do not need to stress about migrating the entire codebase.
---
# Method names starting with **get**
Here is the Java class:
```java
public interface DemoService {
@GET("posts")
Observable getDemoResponse();
@GET("categories")
Observable getDemoResponse2();
}
```
---
# Method names starting with **get**
```kotlin
interface DemoService {
@get:GET("posts")
val demoResponse: Observable
@get:GET("categories")
val demoResponse2: Observable
}
```
Expecting methods **demoResponse** and **demoResponse2**, They are being interpreted as getter methods, this will cause lots of issues.
---
# No **ArgumentCaptor**
If you are using Mockito’s ArgumentCaptor you will most probably get following error
```
java.lang.IllegalStateException: classCaptor.capture() must not be null
```
---
# No **ArgumentCaptor**
If you are using Mockito’s ArgumentCaptor you will most probably get following error
```
java.lang.IllegalStateException: classCaptor.capture() must not be null
```
The return value of **classCaptor.capture()** is null, but the signature of **SomeClass#someMethod(Class, Boolean)** does not allow a *null* argument.
---
# No **ArgumentCaptor**
If you are using Mockito’s ArgumentCaptor you will most probably get following error
```
java.lang.IllegalStateException: classCaptor.capture() must not be null
```
The return value of **classCaptor.capture()** is null, but the signature of **SomeClass#someMethod(Class, Boolean)** does not allow a *null* argument.
**[mockito-kotlin](https://github.com/nhaarman/mockito-kotlin)** library provides supporting functions to solve this problem
---
# Key **Takeaways**
* **annotationProcessor** must be replaced by **kapt** in build.gradle
---
# Key **Takeaways**
* **annotationProcessor** must be replaced by **kapt** in build.gradle
* Configure tests to mock final classes
---
# Key **Takeaways**
* **annotationProcessor** must be replaced by **kapt** in build.gradle
* Configure tests to mock final classes
* If you are using android **data-binding**, include:
```groovy
kapt com.android.databinding:compiler:3.0.0
```
---
# Key **Takeaways**
* **annotationProcessor** must be replaced by **kapt** in build.gradle
* Configure tests to mock final classes
* If you are using android **data-binding**, include:
```groovy
kapt com.android.databinding:compiler:3.0.0
```
* `@JvmField` to rescue while using ButterKnife `@InjectView` and Espresso `@Rule`
---
# Eliminate all **!!** from your **Kotlin** code
1. Use **val** instead of **var**
2. Use **lateinit**
3. Use **let** function
4. User **Elivis** operator
---
# Use **val** instead of **var**
* Kotlin makes you think about immutability on the language level and that’s great.
* *var* and *val* mean "writable" and "read-only"
* If you use them as immutables, you don’t have to care about nullability.
---
# Use **lateinit**
```kotlin
private var adapter: RecyclerAdapter? = null
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
mAdapter = RecyclerAdapter(R.layout.item_droid)
}
fun updateTransactions() {
adapter!!.notifyDataSetChanged()
}
```
---
# Use **lateinit**
```kotlin
private lateinit var adapter: RecyclerAdapter
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
mAdapter = RecyclerAdapter(R.layout.item_droid)
}
fun updateTransactions() {
adapter?.notifyDataSetChanged()
}
```
---
# Use **let** function
```kotlin
private var photoUrl: String? = null
fun uploadClicked() {
if (photoUrl != null) {
uploadPhoto(photoUrl!!)
}
}
```
---
# Use **let** function
```kotlin
private var photoUrl: String? = null
fun uploadClicked() {
photoUrl?.let { uploadPhoto(it) }
}
```
---
# User **Elivis** operator
Elvis operator is great when you have a fallback value for the null case. So you can replace this:
```kotlin
fun getUserName(): String {
if (mUserName != null) {
return mUserName!!
} else {
return "Anonymous"
}
}
```
----
# User **Elivis** operator
Elvis operator is great when you have a fallback value for the null case. So you can replace this:
```kotlin
fun getUserName(): String {
return mUserName ?: "Anonymous"
}
```
---
# Kotlin Extensions
```kotlin
Toast.makeText(context, "Hello #BlrKotlin :)", Toast.LENGTH_LONG).show()
```
---
# Kotlin Extensions
```kotlin
Toast.makeText(context, "Hello #BlrKotlin :)", Toast.LENGTH_LONG).show()
```
```kotlin
/**
* Extension method to show toast for Context.
*/
fun Context?.toast(@StringRes textId: Int, duration: Int = Toast.LENGTH_LONG) =
this?.let { Toast.makeText(it, textId, duration).show() }
```
---
# Kotlin Extensions
```kotlin
Toast.makeText(context, "Hello #BlrKotlin :)", Toast.LENGTH_LONG).show()
```
```kotlin
/**
* Extension method to show toast for Context.
*/
fun Context?.toast(@StringRes textId: Int, duration: Int = Toast.LENGTH_LONG) =
this?.let { Toast.makeText(it, textId, duration).show() }
```
Check [http://kotlinextensions.com/](http://kotlinextensions.com/)
---
# Kotlin Android Extensions
* Goodbye **`findViewById`**
* Using **`Parcelize`** annotation for Parcelable
---
# Kotlin Android Extensions
* Goodbye **`findViewById`**
* Using **`Parcelize`** annotation for Parcelable
```groovy
apply plugin: 'com.android.application'
apply plugin: 'kotlin-android'
apply plugin: 'kotlin-android-extensions'
```
---
## Goodbye **`findViewById`**
```xml
```
---
# Goodbye **`findViewById`**
```kotlin
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
setContentView(R.layout.activity_main)
TextView welcomeMessageView = findViewById(R.id.welcomeMessage),
welcomeMessageView.text = "Hello BlrKotlin!"
}
```
---
# Goodbye **`findViewById`**
```kotlin
import kotlinx.android.synthetic.main.activity_main.*
```
---
# Goodbye **`findViewById`**
```kotlin
import kotlinx.android.synthetic.main.activity_main.*
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
setContentView(R.layout.activity_main)
welcomeMessage.text = "Hello BlrKotlin!"
}
```
---
# Using Parcelize annotation for Parcelable
Here is the Java Class:
```java
public class MyParcelable implements Parcelable {
private int mData;
public int describeContents() { return 0; }
public void writeToParcel(Parcel out, int flags) { out.writeInt(mData); }
public static final Parcelable.Creator CREATOR
= new Parcelable.Creator() {
public MyParcelable createFromParcel(Parcel in) { return new MyParcelable(in); }
public MyParcelable[] newArray(int size) { return new MyParcelable[size];}
};
private MyParcelable(Parcel in) { mData = in.readInt(); }
}
```
---
# Using Parcelize annotation for Parcelable
Converted Kotlin Class:
```kotlin
data class MyParcelable(var data: Int): Parcelable {
override fun describeContents() = 1
override fun writeToParcel(dest: Parcel, flags: Int) { dest.writeInt(data)}
companion object {
@JvmField
val CREATOR = object : Parcelable.Creator {
override fun createFromParcel(source: Parcel): MyParcelable {
val data = source.readInt(); return MyParcelable(data)
}
override fun newArray(size: Int) = arrayOfNulls(size)
}
}
}
```
---
# Using `Parcelize` annotation for Parcelable
To use `@Parcelize` we need to set experimental flag in `build.gradle`
```groovy
androidExtensions {
experimental = true
}
```
---
# Using `Parcelize` annotation for Parcelable
To use `@Parcelize` we need to set experimental flag in `build.gradle`
```groovy
androidExtensions {
experimental = true
}
```
```kotlin
@Parcelize
class MyParcelable(val data: Int): Parcelable
```
---
# Final tip
---
# Final tip
> Don’t try to learn the whole language at once
---
# Questions?
---
### Thank You
---
# **Android Testing Guide**
* Everything to start writing tests for Android App.
* 75% discount on my upcoming book use [BLRKOTLIN](https://leanpub.com/android-testing/c/BLRKOTLIN)
* https://leanpub.com/android-testing/c/BLRKOTLIN
