Dagger Hilt Android Example kotlin

To understand the concept we use the same example where a Car class depends on an Engine class.


1/  Create A New Project.

2/ Modify build.gradle.kts (app level)

add -> 

               id("kotlin-kapt")

       id("dagger.hilt.android.plugin")

add -> below two dependency
       implementation("com.google.dagger:hilt-android:2.51.1")

       kapt("com.google.dagger:hilt-android-compiler:2.51.1")

plugins {
    alias(libs.plugins.android.application)
    alias(libs.plugins.kotlin.android)
    id("kotlin-kapt")
    id("dagger.hilt.android.plugin")
}

android {
    namespace = "com.zissofworks.daggerhiltandroidexamplekotlin"
    compileSdk = 35

    defaultConfig {
        applicationId = "com.zissofworks.daggerhiltandroidexamplekotlin"
        minSdk = 28
        targetSdk = 34
        versionCode = 1
        versionName = "1.0"

        testInstrumentationRunner = "androidx.test.runner.AndroidJUnitRunner"
    }

    buildTypes {
        release {
            isMinifyEnabled = false
            proguardFiles(
                getDefaultProguardFile("proguard-android-optimize.txt"),
                "proguard-rules.pro"
            )
        }
    }
    compileOptions {
        sourceCompatibility = JavaVersion.VERSION_1_8
        targetCompatibility = JavaVersion.VERSION_1_8
    }
    kotlinOptions {
        jvmTarget = "1.8"
    }
}

dependencies {

    implementation(libs.androidx.core.ktx)
    implementation(libs.androidx.appcompat)
    implementation(libs.material)
    implementation(libs.androidx.activity)
    implementation(libs.androidx.constraintlayout)
    testImplementation(libs.junit)
    androidTestImplementation(libs.androidx.junit)
    androidTestImplementation(libs.androidx.espresso.core)

    implementation("com.google.dagger:hilt-android:2.51.1")
    kapt("com.google.dagger:hilt-android-compiler:2.51.1")
}

3/ Modify build.gradle.kts (project level)

add ->   id("com.google.dagger.hilt.android") version "2.51.1" apply false

// Top-level build file where you can add configuration options common to all sub-projects/modules.
plugins {
    alias(libs.plugins.android.application) apply false
    alias(libs.plugins.kotlin.android) apply false
    id("com.google.dagger.hilt.android") version "2.51.1" apply false
}

4/ Create a class Engine with @Inject annotation

package com.zissofworks.daggerhiltandroidexamplekotlin

import android.util.Log
import javax.inject.Inject

class Engine @Inject constructor() {
    fun start(){
        Log.d("DaggerHiltExample", "Engine Start")
    }
}

5/  Create a class Car with @Inject annotation and this class is dependent on the Engine class taking the Engine class object as a parameter

package com.zissofworks.daggerhiltandroidexamplekotlin

import android.util.Log
import javax.inject.Inject

class Car @Inject constructor(private val engine: Engine) {
    fun drive(){
        engine.start()
        Log.d("DaggerHiltExample", "car drive")
    }
}

6/ Create a class MyApplication which extends the Application. Annotation this class with @HiltAndroidApp  and add on manifest file.

It ensures that the hilt is properly initialized for your application. And this step is mandatory.

package com.zissofworks.daggerhiltandroidexamplekotlin

import android.app.Application
import dagger.hilt.android.HiltAndroidApp

@HiltAndroidApp
class MyApplication : Application() {

}

7/ Add the MyApplication in AndroidManifest.xml file application tag

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools">

    <application
        android:name=".MyApplication"
        android:allowBackup="true"
        android:dataExtractionRules="@xml/data_extraction_rules"
        android:fullBackupContent="@xml/backup_rules"
        android:icon="@mipmap/ic_launcher"
        android:label="@string/app_name"
        android:roundIcon="@mipmap/ic_launcher_round"
        android:supportsRtl="true"
        android:theme="@style/Theme.DaggerHiltAndroidExampleKotlin"
        tools:targetApi="31">
        <activity
            android:name=".MainActivity"
            android:exported="true">
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />

                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>
    </application>

</manifest>

8/ Modify MainActivity.Kt

   here we just add the variable for the Car object and never initialize or create the object. Dagger will provide the instance of Car by the @Inject annotation. We don't need to do it manually. 

Annotation with @AndroidEntryPoint with this activity.

package com.zissofworks.daggerhiltandroidexamplekotlin

import android.os.Bundle
import androidx.activity.enableEdgeToEdge
import androidx.appcompat.app.AppCompatActivity
import androidx.core.view.ViewCompat
import androidx.core.view.WindowInsetsCompat
import dagger.hilt.android.AndroidEntryPoint
import javax.inject.Inject

@AndroidEntryPoint
class MainActivity : AppCompatActivity() {

    @Inject
    lateinit var car: Car

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        enableEdgeToEdge()
        setContentView(R.layout.activity_main)
        ViewCompat.setOnApplyWindowInsetsListener(findViewById(R.id.main)) { v, insets ->
            val systemBars = insets.getInsets(WindowInsetsCompat.Type.systemBars())
            v.setPadding(systemBars.left, systemBars.top, systemBars.right, systemBars.bottom)
            insets
        }

        car.drive()
    }
}