this is a non-work-related homework n00b dagger2 problem (please accord it only that much respect :)

[Eric Flatt]

I decided to kill a bunch birds w/ one stone and use java (which I never do) and dagger2 (which I never have) in some homework problem for a machine learning class I'm taking.  The problem I have here is lifted from the web as a toy example to simplify things down.  I basically have a Bar class that has a dependency on a BarDatabase (I forget where I stole the example from).

Problem is, I think I've done all the right steps (see below), but when push comes to shove in my MainActivity (doing this in android studio) and Dagger_BarComponent should be there to autocomplete or bind, it isn't.  The code isn't getting generated.  Please waste little time on this, but if something obvious sprung up, I wanted to ask.

1. Here's my bar module BarModule.java:

/**
 * Created by eflatt on 4/26/16.
 */
@Module
public class BarModule {

    @Provides @Singleton
    BarDatabase provideBarDatabase () {
        return new BarDatabase();
    }

    @Provides @Singleton
    Bar provideBar () {
        return new Bar(new BarDatabase());
    }
}

2.  Here's me @Injecting the ctor in Bar.java:

public class Bar {
    // Bar depends on BarDatabase
    private BarDatabase db;

    @Inject
    public Bar(BarDatabase db) {
        this.db = db;
    }

    public BarDatabase getBar() { return db; }

    public Cocktail getCocktail(String name) {
        String row = db.getCocktail(name);
        return new Cocktail(row);
    }
}

3.  Here's my BarComponent.java (where I define the component, naturally):

/**
 * Created by eflatt on 4/26/16.
 */
@Singleton
@Component(modules = {BarModule.class})
public interface BarComponent {
    Bar provideBar();
}

4.  But when I try to use it in my MainActivity.java:

BarComponent component = Dagger   // broken, it can't find the component, so no autocomplete, no dagger.

My build.gradle files look like this:

// Top-level build file where you can add configuration options common to all sub-projects/modules.

buildscript {
    repositories {
        jcenter()
    }
    dependencies {
        classpath 'com.android.tools.build:gradle:2.0.0'

        // Assists in working with annotation processors for Android Studio.
        classpath 'com.neenbedankt.gradle.plugins:android-apt:1.4'
    }
}

allprojects {
    repositories {
        jcenter()
    }
}

task clean(type: Delete) {
    delete rootProject.buildDir
}

and my app level build.gradle:
apply plugin: 'com.android.application'

// Assists in working with annotation processors for Android Studio.
apply plugin: 'com.neenbedankt.android-apt'

android {
    compileSdkVersion 23
    buildToolsVersion "23.0.3"

    defaultConfig {
        applicationId "com.example.eflatt.di"
        minSdkVersion 19
        targetSdkVersion 23
        versionCode 1
        versionName "1.0"
    }
    buildTypes {
        release {
            minifyEnabled false
            proguardFiles getDefaultProguardFile('proguard-android.txt'), 'proguard-rules.pro'
        }
    }
}

dependencies {
    compile fileTree(dir: 'libs', include: ['*.jar'])
    testCompile 'junit:junit:4.12'
    compile 'com.android.support:appcompat-v7:23.3.0'

    // Dagger 2 and Compiler
    compile 'com.google.dagger:dagger:2.0.1'
    apt "com.google.dagger:dagger-compiler:2.0.1"

    // Needed for @Generated annotation (missing in Android API jar)
    // No longer needed in dagger >= 2.1-SNAPSHOT (github.com/google/dagger/issues/95)
    compile 'javax.annotation:jsr250-api:1.0'
}

[David P. Baker]

I see some problems with your component, but they shouldn't lead to a build error.

1. Bar has an @Inject constructor, but you also have a @Provides method that returns a Bar. In any component with that @Provides method, the @Inject constructor will be ignored. (A @Provides method takes precedence.)
   
2. The @Provides method that returns a Bar calls new BarDatabase() explicitly, rather than letting Dagger call the constructor. If you want to use a @Provides method for Bar, it should take dependencies as parameters:
   
   @Provides static Bar provideBar(BarDatabase barDatabase) {
     return new Bar(barDatabase);
   }
   
   (Also, making @Provides methods static like this lets Dagger skip instantiating the module at all.)

I don't know Gradle, but I see you have some annotation processors configured there. Do you have to apply Dagger as well?

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