part-1.md

Hilt (Part 1)

Get dependencies

https://developer.android.com/training/dependency-injection/hilt-android

In project level build.gradle file

buildscript {

    ext.dagger_version = "2.38.1"
    
    // ...
    
    dependencies {
        // ...
        classpath "com.google.dagger:hilt-android-gradle-plugin:$dagger_version"
        
    }
}

In app level build.gradle file

plugins {
    // ...
    id 'kotlin-kapt'
    id 'dagger.hilt.android.plugin'
}

// ...

dependencies {
    // ...
    implementation "com.google.dagger:hilt-android:$dagger_version"
    kapt "com.google.dagger:hilt-compiler:$dagger_version"
}

Initialise Application class

• Create application class and add @HiltAndroidApp annotation.

  @HiltAndroidApp
  class BaseApplication: Application() {
  }
  

• Add to manifest.

  <manifest ...
    >
  
    <application
        android:name=".BaseApplication"
        ...
        >
  
        ...
  
    </application>
  
  </manifest>
  

Simple FIELD injection

• Activities / Fragment / Service / custom views, i.e. all android framework receiving an injection needs the @AndroidEntryPoint annotation

  @AndroidEntryPoint
  class MainActivity: AppCompatActivity() {
  

• The lateinit var into which injection is performed @Inject annotation.

  @Inject
  lateinit var testClass: TestClass
  

• The source class, whose instance is being injected, must also have the @Inject annotation above its constructor.

  class TestClass
  @Inject
  constructor()
  {
    ...
  }
  

Full FIELD injection sample

@AndroidEntryPoint
class MainActivity: AppCompatActivity() {

    @Inject
    lateinit var testClass: TestClass

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        println("Result: ${testClass.getSampleString()}")
    }

}

class TestClass
@Inject
constructor()
/*
 * Note that even though the constructor is empty (constructor would not have been normally needed),
 * but since we are using dependency injection, we need the @Inject annotation, on a contructor.
 */
{
    fun getSampleString() = "A sample string"
}

Simple CONSTRUCTOR injection

Almost same as above. Add @Inject annotation above the constructor where the injection is to be performed.

@AndroidEntryPoint
class MainActivity: AppCompatActivity() {

    @Inject
    lateinit var testClassAdd: TestClassAdd

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        println("Result: ${testClassAdd.getStringAddition()}")
    }

}

class TestClassAdd
@Inject             // CONSTRUCTOR INJECTION
constructor(private val n1: RandomNumberClass, private val n2: RandomNumberClass){
    fun getStringAddition() =
        "Number 1: ${n1.value}, Number 2: ${n2.value}, Addition: ${n1.value + n2.value}"
}

class RandomNumberClass
@Inject
constructor()
{
    val value = (Math.random()*100).toInt()
}

WARNING!

The source class (in the above example RandomNumberClass) cannot have constructor arguments.
Check Part 2