Passing Application Context in Activity in Dagger 2 (NullPointerException)

Question

I am trying to pass Application context Activity in Dagger 2. Any bits of help is well appreciated!! I have provided my Logcat console at the end.

The project by Gregory Kick gives me the same problem as shown below at last error section. https://github.com/gk5885/dagger-android-sample

I have also tried to improve based on this issue: https://github.com/google/dagger/issues/832

Nothing worked! I know Application context is, actually, not needed in Activity because there is Activity context in the Activity. But just curious to learn how can I pass Application context in any classes (for instance, Activity)?

apply plugin: 'com.android.application'

android {
    compileSdkVersion 27
    buildToolsVersion "27.0.3"

    testBuildType "staging"

    testOptions {
        reportDir "$rootDir/test-reports"
        resultsDir "$rootDir/test-results"
        unitTests {
            returnDefaultValues true
            all {
                // Sets JVM argument(s) for the test JVM(s).
                jvmArgs '-XX:MaxPermSize=256m'

                // You can also check the task name to apply options to only the tests you specify.
                if (it.name == 'testDebugUnitTest') {
                    systemProperty 'debug', 'true'
                }
            }
        }
    }
    defaultConfig {
        applicationId "com.nexuslab.forensics.grr.nanny"
        minSdkVersion 21
        targetSdkVersion 27
        versionCode 1
        versionName "1.0"
        testInstrumentationRunner "android.support.test.runner.AndroidJUnitRunner"

        testHandleProfiling true
        testFunctionalTest true
    }
    signingConfigs {
        debugKey {
            keyAlias 'android'
            keyPassword 'android'
            storeFile file('keys/platform.jks')
            storePassword 'android'
        }
    }
    buildTypes {
        debug {
            signingConfig signingConfigs.debugKey
        }
        release {
            minifyEnabled false
            proguardFiles getDefaultProguardFile('proguard-android.txt'), 'proguard-rules.pro'
        }
        staging {
            minifyEnabled false
            proguardFiles getDefaultProguardFile('proguard-android.txt'), 'proguard-rules.pro'
        }
    }

    compileOptions {
        sourceCompatibility JavaVersion.VERSION_1_7
        targetCompatibility JavaVersion.VERSION_1_7
    }
    configurations.all {
        resolutionStrategy.force 'com.google.code.findbugs:jsr305:1.3.9'
    }
}

dependencies {
    implementation fileTree(include: ['*.jar'], dir: 'libs')
    implementation 'com.android.support:appcompat-v7:27.1.0'
    implementation 'com.android.support.constraint:constraint-layout:1.0.2'
    compileOnly 'org.projectlombok:lombok:1.16.20'
    annotationProcessor 'org.projectlombok:lombok:1.16.20'
    //java vm based test
    testImplementation 'org.hamcrest:hamcrest-core:1.3'
    testImplementation 'junit:junit:4.12'
    testImplementation 'org.powermock:powermock-api-mockito:1.6.5'
    testImplementation 'org.powermock:powermock-module-junit4-rule-agent:1.6.5'
    testImplementation 'org.powermock:powermock-module-junit4-rule:1.6.5'
    testImplementation 'org.powermock:powermock-module-junit4:1.6.5'
    testImplementation 'org.mockito:mockito-core:2.15.0'
    //instrumentation test
    androidTestImplementation 'com.android.support.test:runner:1.0.1'
    androidTestImplementation 'com.android.support.test.espresso:espresso-core:3.0.1'
    androidTestImplementation 'com.android.support:support-annotations:27.1.0'
    androidTestImplementation 'com.android.support.test:runner:1.0.1'
    androidTestImplementation 'com.android.support.test:rules:1.0.1'
    androidTestImplementation 'org.hamcrest:hamcrest-library:1.3'
    androidTestImplementation 'com.android.support.test.uiautomator:uiautomator-v18:2.1.3'
    androidTestImplementation 'junit:junit:4.12'
    //dagger 2
    implementation 'com.google.dagger:dagger:2.14.1'
    annotationProcessor 'com.google.dagger:dagger-compiler:2.14.1'
    //to enable DaggerActivity, DaggerBroadcastReceiver, DaggerFragment etc classes
    implementation 'com.google.dagger:dagger-android:2.14.1'
    annotationProcessor 'com.google.dagger:dagger-android-processor:2.14.1'
    //support libraries with dagger 2
    implementation 'com.google.dagger:dagger-android-support:2.14.1'
    implementation 'com.android.support:support-v4:27.1.0'
}

Application class (NannyApplication.java)

package com.nexuslab.forensics.grr.nanny;

import android.app.Application;

import com.nexuslab.forensics.grr.nanny.di.component.DaggerNannyApplicationComponent;
/**
 * Created by gaute on 3/25/18.
 */

public class NannyApplication extends Application {

    @Override
    public void onCreate() {
        super.onCreate();
        DaggerNannyApplicationComponent.builder().create(this);
    }
}

MainActivity.java (Here, I want to inject context from NannyApplication.java)

package com.nexuslab.forensics.grr.nanny;

import android.os.Bundle;
import android.support.annotation.Nullable;
import android.support.v7.app.AppCompatActivity;

import javax.inject.Inject;

/**
 * @author gaute
 */
public class MainActivity extends AppCompatActivity {

    @Inject
    NannyApplication nannyApplication;

    @Override
    protected void onCreate(@Nullable Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
    }

    @Override
    protected void onStart() {
        super.onStart();
        Utils.schedule(nannyApplication, HeartbeatService.class, Constants.HEARTBEAT_CHECK_INTERVAL);
        finishAndRemoveTask();
    }

}

Dagger Application Component (NannyApplicationComponent.java)

package com.nexuslab.forensics.grr.nanny.di.component;


import com.nexuslab.forensics.grr.nanny.NannyApplication;
import com.nexuslab.forensics.grr.nanny.di.module.NannyApplicationModule;

import javax.inject.Singleton;

import dagger.Component;
import dagger.android.AndroidInjector;

/**
 * Created by gaute on 3/25/18.
 */

@Singleton
@Component(modules = NannyApplicationModule.class)
public interface NannyApplicationComponent extends AndroidInjector<NannyApplication> {

    @Component.Builder
    abstract class Builder extends AndroidInjector.Builder<NannyApplication> {
    }
}

Application Module (NannyApplicationModule.java)

package com.nexuslab.forensics.grr.nanny.di.module;

import com.nexuslab.forensics.grr.nanny.NannyApplication;

import javax.inject.Singleton;

import dagger.Module;
import dagger.Provides;
import dagger.android.AndroidInjectionModule;

@Module(includes = AndroidInjectionModule.class)
public class NannyApplicationModule {

    @Provides
    @Singleton
    NannyApplication getNannyApplication(NannyApplication nannyApplication) {
        return nannyApplication;
    }

}

Error, I got

03-27 19:08:37.107 10619-10619/com.nexuslab.forensics.grr.nanny E/AndroidRuntime: FATAL EXCEPTION: main
    Process: com.nexuslab.forensics.grr.nanny, PID: 10619
    java.lang.RuntimeException: Unable to start activity ComponentInfo{com.nexuslab.forensics.grr.nanny/com.nexuslab.forensics.grr.nanny.MainActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'java.lang.String[] com.nexuslab.forensics.grr.nanny.NannyApplication.databaseList()' on a null object reference
        at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2946)
        at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3046)
        at android.app.ActivityThread.-wrap11(Unknown Source:0)
        at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1688)
        at android.os.Handler.dispatchMessage(Handler.java:105)
        at android.os.Looper.loop(Looper.java:164)
        at android.app.ActivityThread.main(ActivityThread.java:6809)
        at java.lang.reflect.Method.invoke(Native Method)
        at com.android.internal.os.Zygote$MethodAndArgsCaller.run(Zygote.java:240)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:767)
     Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'java.lang.String[] com.nexuslab.forensics.grr.nanny.NannyApplication.databaseList()' on a null object reference
        at com.nexuslab.forensics.grr.nanny.MainActivity.onStart(MainActivity.java:26)
        at android.app.Instrumentation.callActivityOnStart(Instrumentation.java:1412)
        at android.app.Activity.performStart(Activity.java:7015)
        at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2909)
        at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3046) 
        at android.app.ActivityThread.-wrap11(Unknown Source:0) 
        at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1688) 
        at android.os.Handler.dispatchMessage(Handler.java:105) 
        at android.os.Looper.loop(Looper.java:164) 
        at android.app.ActivityThread.main(ActivityThread.java:6809) 
        at java.lang.reflect.Method.invoke(Native Method) 
        at com.android.internal.os.Zygote$MethodAndArgsCaller.run(Zygote.java:240) 
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:767) 

I Can't use any sorts of constructor injection in an Activity as below.

 private NannyApplication nannyApplication;

    @Inject
    public MainActivity() {
        this.nannyApplication = nannyApplication;
    }

That's why I used filed injection:

@Inject NannyApplication nannyApplication; //Problem here

Answer 1

This is a working solution.

Rule: For any Service Component T, we must provide T’s instance as a seedInstance into the AndroidInjector.Builder<T> class. It means if you do AndroidInjector.inject(this) inside MainActivity's lifecycle callback, you initialized seedInstance = mainActivity inside AndroidInjector.Builder<MainActivity> class.

This AndroidInjector.Builder<MainActivity>, you will see inside the DaggerNannyApplicationComponent's Builder inner class because, in the NannyApplicationComponent, you will gonna write

@Component.Builder /* Simply tells this Builder is DaggerNannyApplicationComponent’s inner Builder class */
    abstract class Builder extends AndroidInjector.Builder<NannyApplication> {
    } 

The Sample project in Github: https://github.com/uddhavgautam/Dagger2ApplicationContextToActivity

NannyApplicationComponent.java

@Singleton
@Component(modules = {
        AndroidSupportInjectionModule.class /* it makes Dagger generates DaggerNannyApplicationComponent */,
        ApplicationBindingModule.class /* it generats AndroidInjector.Builder<MainActivity>, which
        is used to inject requested dependencies by MainActivity */
})
public interface NannyApplicationComponent extends AndroidInjector<NannyApplication> {

    @Component.Builder /* Simply tells this Builder is DaggerNannyApplicationComponent’s inner Builder class */
    abstract class Builder extends AndroidInjector.Builder<NannyApplication> {
    }
}

ApplicationBindingModule.java

 @Module
    public interface ApplicationBindingModule {

/* These two lines, actually, makes Dagger generates ApplicationBindingModule_MainActivity class */
        @ContributesAndroidInjector
        MainActivity mainActivity();
    }

NannyApplicationModule.java

@Module
public class NannyApplicationModule {
}

MainActivity.java

//MainActivity is a consumer because it has requested nannyApplication using @Inject annotation
public class MainActivity extends DaggerAppCompatActivity {

    @Inject
    NannyApplication nannyApplication /* You got the ApplicationContext */;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        // AndroidInjection.inject(this); 
/* if Consumers want MainActivity instance then uncomment AndroidInjection.inject(this) line. Doing this makes MainActivity Consumer as well as Service component. Because it consumed nannyApplication but it has also provided (serviced) it's instance to the external world */
    }

    @Override
    protected void onStart() {
        super.onStart();
        //check nannyApplication
        Log.i("Cls-loader: ", nannyApplication.getClassLoader() + "");
    }
}

NannyApplication.java

public class NannyApplication extends DaggerApplication {

    @Override
    public void onCreate() {
        super.onCreate();
    }

    /**
     * applicationInjector() gets called inside onCreate()
     */
    @Override
    protected AndroidInjector<? extends DaggerApplication> applicationInjector() {
        return DaggerNannyApplicationComponent
                .builder()
                .create(this);
    }
}