I&#39;ve just published sample app based on Gradle which integrates Dagger2, retrolambda, butterknife and lombok. You can find it here: https://github.com/mgrzechocinski/dagger2-example. 

Hope it would help :)


I&#39;ve just ported [u2020-mvp][1] app to Dagger 2. We use it as our sandbox app. Dagger 2 has nice implementation of scopes by the way. Components are really big deal. 
And it is based on [u2021][2] made by Christian Gruber. You can check that as well.

Hope it helps :)


  [1]: https://github.com/LiveTyping/u2020-mvp
  [2]: https://github.com/cgruber/u2020/tree/dagger2

For anyone looking for a simple and straightforward way to just build a Dagger 2 project on Gradle/Android Studio, check out https://github.com/bytehala/dagger2-gradle-quickstart

In the [commit messages][1], I also enumerate the steps to convert a fully functioning project to Dagger 2.

&gt; The target audience for this project is anyone who has no experience with dependency injection.

No other library besides Butterknife is used.

**WARNING**
The aim of this sample project is simplicity, not completeness.
Only the following features were used:

 - @Module
 - @Component
 - @Injects
 - @Provides
 - @Singleton

Topics such as scopes, submodules, etc are left as an exercise.


  [1]: https://github.com/bytehala/dagger2-gradle-quickstart/commits/master

CoffeeMaker sample without android: https://github.com/yongjhih/dagger2-sample

Steps:

    git clone https://github.com/yongjhih/dagger2-sample
    cd dagger2-sample
    ./gradlew execute



I have, what I think to be, a very simple Spring WebSocket application.  However, I&#39;m trying to use path variables for the subscription as well as the message mapping.

I&#39;ve posted a paraphrased example  below. I would expect the `@SendTo` annotation to return back to the subscribers based on their `fleetId`.  ie, a `POST` to `/fleet/MyFleet/driver/MyDriver` should notify subscribers of `/fleet/MyFleet`, but I&#39;m not seeing this behavior.

It&#39;s worth noting that subscribing to literal `/fleet/{fleetId}` works.  Is this intended?  Am I missing some piece of configuration?  Or is this just not how it works?

I&#39;m not very familiar with WebSockets or this Spring project yet, so thanks in advance.

**Controller.java**

    ...
    @MessageMapping(&quot;/fleet/{fleetId}/driver/{driverId}&quot;)
	@SendTo(&quot;/topic/fleet/{fleetId}&quot;)
	public Simple simple(@DestinationVariable String fleetId, @DestinationVariable String driverId) {
		return new Simple(fleetId, driverId);
	}
    ...


**WebSocketConfig.java**

    @Configuration
    @EnableWebSocketMessageBroker
    public class WebSocketConfig extends AbstractWebSocketMessageBrokerConfigurer {
    	@Override
    	public void configureMessageBroker(MessageBrokerRegistry config) {
    		config.enableSimpleBroker(&quot;/topic&quot;);
    		config.setApplicationDestinationPrefixes(&quot;/live&quot;);
    	}
    
    	@Override
    	public void registerStompEndpoints(StompEndpointRegistry registry) {
    		registry.addEndpoint(&quot;/fleet&quot;).withSockJS();
    	}
    }

**index.html**

	var socket = new SockJS(&#39;/fleet&#39;);
	var stompClient = Stomp.over(socket);
	stompClient.connect({}, function(frame) {
        // Doesn&#39;t Work
        stompClient.subscribe(&#39;/topic/fleet/MyFleet&#39;, function(greeting) {
        // Works
		stompClient.subscribe(&#39;/topic/fleet/{fleetId}&#39;, function(greeting) {
			// Do some stuff
		});
	});

**Send Sample**

		stompClient.send(&quot;/live/fleet/MyFleet/driver/MyDriver&quot;, {}, JSON.stringify({
			// Some simple content
		}));

Path variables in Spring WebSockets @SendTo mapping

I have some `bytes`.

    b&#39;\x01\x02\x03&#39;

And an `int` in range 0..255.

    5

Now I want to append the `int` to the `bytes` like this:

    b&#39;\x01\x02\x03\x05&#39;

How to do it? There is no `append` method in `bytes`. I don&#39;t even know how to make the integer become a single byte.

    &gt;&gt;&gt; bytes(5)
    b&#39;\x00\x00\x00\x00\x00&#39;

How to append to bytes in python 3

Dagger 2 is around the corner but the available examples wouldn&#39;t even compile right off the box, and the documentation is a copy-paste-replace from Dagger 1.

Does anyone have an example of a proper application working on Google&#39;s Dagger 2?

Dagger 2 examples

<p>Dagger 2 is around the corner but the available examples wouldn't even compile right off the box, and the documentation is a copy-paste-replace from Dagger 1.</p>
<p>Does anyone have an example of a proper application working on Google's Dagger 2?</p>


I try to use the `CardView` and it works well below 5.0, but looks strange on Lollipop.

![enter image description here][1]


![enter image description here][2]


  [1]: http://i.stack.imgur.com/Ww4QH.png
  [2]: http://i.stack.imgur.com/uhjLN.png

    &lt;?xml version=&quot;1.0&quot; encoding=&quot;utf-8&quot;?&gt;
    &lt;LinearLayout xmlns:android=&quot;http://schemas.android.com/apk/res/android&quot;
    android:layout_width=&quot;match_parent&quot;
    android:layout_height=&quot;match_parent&quot;
    android:orientation=&quot;vertical&quot;
    android:paddingBottom=&quot;@dimen/activity_vertical_margin&quot;
    android:paddingLeft=&quot;@dimen/activity_horizontal_margin&quot;
    android:paddingRight=&quot;@dimen/activity_horizontal_margin&quot;
    android:paddingTop=&quot;@dimen/activity_vertical_margin&quot;&gt;

    &lt;android.support.v7.widget.CardView android:layout_width=&quot;match_parent&quot;
        android:layout_height=&quot;200dp&quot;&gt;
        &lt;TextView
            android:id=&quot;@+id/textView&quot;
            android:layout_width=&quot;wrap_content&quot;
            android:layout_height=&quot;wrap_content&quot;
            android:text=&quot;card1&quot;
            android:textAppearance=&quot;?android:attr/textAppearanceLarge&quot; /&gt;
    &lt;/android.support.v7.widget.CardView&gt;
    &lt;android.support.v7.widget.CardView android:layout_width=&quot;match_parent&quot;
        android:layout_height=&quot;200dp&quot;&gt;

        &lt;TextView
            android:id=&quot;@+id/textView2&quot;
            android:layout_width=&quot;wrap_content&quot;
            android:layout_height=&quot;wrap_content&quot;
            android:text=&quot;card2&quot;
            android:textAppearance=&quot;?android:attr/textAppearanceLarge&quot; /&gt;
    &lt;/android.support.v7.widget.CardView&gt;
    &lt;/LinearLayout&gt;

I meet the same question when i use the `RecyclerView`, should I have to add something if it runs on Lollipop?


Why there is no space between CardViews on Lollipop?

How to use Dagger? How to configure Dagger to work in my Android project?

I&#39;d like to use Dagger in my Android project, but I find it confusing.

EDIT: Dagger2 is also out since 2015 04 15, and it&#39;s even more confusing!


*[This question is a &quot;stub&quot; on which I am adding to my answer as I learned more about Dagger1, and learn more about Dagger2. This question is more of a **guide** rather than a &quot;question&quot;.]*

How to set up DAGGER dependency injection from scratch in Android project?

I&#39;m trying to get the SHA1 fingerprint so I can get an Google API key.
Im in the following directory: 

&gt; /Library/Java/JavaVirtualMachines/jdk1.8.0_20.jdk/Contents/Home/bin

Then I execute the command from the google site : 

&gt; keytool -list -v -keystore mystore.keystore

But it gives this error:

    keytool error: java.lang.Exception: Keystore file does not exist: mystore.keystore
    java.lang.Exception: Keystore file does not exist: mystore.keystore
    	at sun.security.tools.keytool.Main.doCommands(Main.java:742)
    	at sun.security.tools.keytool.Main.run(Main.java:340)
    	at sun.security.tools.keytool.Main.main(Main.java:333)

I followed tutorials but I can&#39;t get it to work!
Does anyone know what I am doing wrong?

BTW: I&#39;m using a Macbook Pro with Xamarin Studio 5.5.2.


Keystore file doesn&#39;t exist

I am using Google notifications in my app, and until now I have done below in the manifest:

    &lt;!-- GCM --&gt;
    &lt;uses-permission android:name=&quot;android.permission.GET_ACCOUNTS&quot; /&gt; &lt;!-- GCM requires a Google account. --&gt;
    &lt;uses-permission android:name=&quot;android.permission.WAKE_LOCK&quot; /&gt; &lt;!-- Keeps the processor from sleeping when a message is received. --&gt; 
    &lt;uses-permission android:name=&quot;com.google.android.c2dm.permission.RECEIVE&quot; /&gt; &lt;!-- This app has permission to register and receive data message. --&gt; 
        
    &lt;!-- Creates a custom permission so only this app can receive its messages. NOTE: APP_PACKAGE.permission.C2D_MESSAGE --&gt;   
    &lt;permission android:name=&quot;com.myapp.permission.C2D_MESSAGE&quot; android:protectionLevel=&quot;signature&quot; /&gt;
    &lt;uses-permission android:name=&quot;com.myapp.permission.C2D_MESSAGE&quot; /&gt;    
    &lt;!-- END GCM --&gt;

It worked perfectly until I updated my Nexus 7 to Android 5.0.  
Now when I try to install the app in this device with Eclipse, I get this error:

&gt;INSTALL_FAILED_DUPLICATE_PERMISSION perm=com.myapp.permission.C2D_MESSAGE pkg=com.myapp

I don&#39;t understand what is wrong? It was working perfectly until Android 5.0.  
I know that I am using `C2D_MESSAGE` in two lines, `permission` and `uses-permission` but I have copied that code from the original Google GCM guide, so it must be fine.

INSTALL_FAILED_DUPLICATE_PERMISSION... C2D_MESSAGE

How to get indeterminate circular indicator for &quot;Scroll up to load more&quot; in a grid RecycleView?

The pattern is described there: http://www.google.com/design/spec/components/progress-activity.html#progress-activity-behavior in &quot;Two-phased loads&quot; and &quot;Example 2: Scroll up to load more&quot; example videos.

I&#39;m trying to accomplish this using the new RecyclerView, but I can&#39;t find a &quot;not-too-hackish&quot; way to do that, firstly because there is not a way to add a footer that cover a full row in the grid. Any suggestions?

Put an indeterminate progressbar as footer in a RecyclerView grid

I use Dagger2 for DI in my android application. I found that I have to write inject method for every class that uses @Inject field. Is there a way that I can just inject the parent class so that I don&#39;t have to call inject on every subclass?
Take Activity for example. I have a `BaseActivity` that that every Activity extends from. Is there a way that I can just create an inject method in the component for BaseActivity and just call inject in BaseActivity&#39;s onCreate, and @inject fields in sub activities get injected automatically?


Can I just inject super class when use dagger2 for dependency injection?

Dagger 1&#39;s `plus()` method is something I used quite often in previous applications, so I understand situations where you might want to have a subcomponent with full access to the parent graphs bindings.

In what situation would it be beneficial to use a *component dependency* instead of a *subcomponent dependency* and why? 

Dagger 2 subcomponents vs component dependencies

From the dagger 2 [Documentation][1] I noticed that you can have a `@Singleton` annotated class. What is the purpose of marking a class as `@Singleton` as I have tried to do this in my code but a singleton object is NOT produced. I&#39;m not clear on what use marking my class with this annotation serves.  

From the documentation please focus on the following statement:

&gt; The @Singleton annotation on an injectable class also serves as
&gt; documentation. It reminds potential maintainers that this class may be
&gt; shared by multiple threads.*

```java  
@Singleton
class CoffeeMaker {
    // ...
}
```

  [1]: http://google.github.io/dagger/

UPDATE: After reviewing froger_mcs answer I see that in Dagger 2 you can provide injections either by a module OR by a constructor injection. So the following class, although not in a module, can be injected:


```java
@Singleton
public class MyClass {
    @Inject
    public MyClass() {
    
    }
}
```

In this version the constructor is injected for us and in an Android activity you would just do the following and it will get provided:

```java
@Inject
MyClass myClass;
//then in onCreate actually inject(this) from your graph of course.
```


Dagger 2 - what is the purpose of a @Singleton annotation class

I&#39;m getting this note in the build whenever I do an inject into a kotlin class (btw, I have a mixed android project with both kotlin and java).

For example, after this gradle task: `compileStagingDebugJavaWithJavac` (StagingDebug is my build variant), I get this message:

&gt; &quot;Note: Generating a MembersInjector or Factory for com.packageNameXXX.CourseDiscoveryMapFragment. Prefer to run the dagger processor over that class instead.&quot;

My **CourseDiscoveryMapFragment** code can be seen here:

    class CourseDiscoveryMapFragment : Fragment(){
    
        @Inject
        lateinit var presenter: CourseDiscoveryMapPresenter
    
        lateinit var mapView: MapView
    
        override fun onCreateView(inflater: LayoutInflater, container: ViewGroup?, savedInstanceState: Bundle?): View? {
    
            val view = inflater.inflate(R.layout.fragment_discovery_map, container, false)
    
            MapsInitializer.initialize(activity)
    
            mapView = view.mapView
            mapView.onCreate(savedInstanceState?.getBundle(BUNDLE_KEY_MAP_STATE))
    
            (activity as BaseActivity)
                    .activityComponent.inject(this)
    }

And my **ActivityComponent** is :

    @ActivityScope
    @Subcomponent(modules = ActivityModule.class)
    public interface ActivityComponent {
    
        void inject(BaseActivity baseActivity);
    
        void inject(CourseDiscoveryMapFragment fragment);
    
        //Exposed to sub-graphs.
        Activity activity();
    }

So, I&#39;m having dagger component and modules written in Java, while having dagger injections in Kotlin.

Is this anything that I should be worried about?

Thank you. 

&quot;Prefer to run the dagger processor over that class instead&quot; in Kotlin

I&#39;m having a problem in understanding why the following code doesn&#39;t work.

I have following project structure:

    @Component(modules = CCModule.class) 
    public interface CComponent {
        XXX getXXX();
    }

where 

    @Module
    public class CCModule {

        @Provides @Singleton
        public XXX provide XXX(){
            return new XXX();
        }
    }

and 

    @Component(dependencies = CComponent.class, modules = AAModule.class) 
    public interface AComponent {
        YYY getYYY();
    }

where

    class YYY {
       @Inject
       public YYY(XXX xxx) {
           ...
       }
    }

I initialize everything as:

    CComponent c_component = Dagger_CComponent.builder().cCModule(new CCModule()).build();

    AComponent a_component = Dagger_AComponent.builder()
            .cComponent(c_component)
            .aAModule(new AAModule())
            .build();

Once compilation takes place i get the following error:

&gt; Error:(11, 1) error:
&gt; com.test.CComponent (unscoped) may not
&gt; reference scoped bindings: @Provides @Singleton
&gt; com.test.XXX
&gt; com.test.CCModule.provideXXX()

What I&#39;m aiming for is to have one component inherit bindings from other components to have the same references to an objects (singletons).

Problems with singletons when using component dependencies

I&#39;m trying to wrap my head around scopes in Dagger 2, specifically the lifecycle of scoped graphs. How do you create a component that will be cleaned up when you leave the scope.

In the case of an Android application, using Dagger 1.x you generally have a root scope at the application level which you&#39;d extend to create a child scope at the activity level.

    public class MyActivity {

        private ObjectGraph mGraph;

        public void onCreate() {
            mGraph = ((MyApp) getApplicationContext())
                .getObjectGraph()
                .plus(new ActivityModule())
                .inject(this);
        }

        public void onDestroy() {
            mGraph = null;
        }
    }

The child scope existed as long as you kept a reference to it, which in this case was the lifecycle of your Activity. Dropping the reference in onDestroy ensured the scoped graph was free to be garbage collected.

**EDIT**

Jesse Wilson recently posted a [mea culpa](https://publicobject.com/2014/11/15/dagger-2-has-components/)

&gt; Dagger 1.0 badly screwed up its scope names ... The @Singleton annotation is used for both root graphs and custom graphs, so it&#39;s tricky to figure out what the actual scope of a thing is.

and everything else I&#39;ve read/heard points towards Dagger 2 improving the way scopes work, but I&#39;m struggling to understand the difference. According to @Kirill Boyarshinov&#39;s comment below, the lifecycle of a component or dependency is still determined, as usual, by concrete references. So is the difference between Dagger 1.x and 2.0 scopes purely a matter of semantic clarity?

## My understanding

### Dagger 1.x

Dependencies were either `@Singleton` or not. This was equally true of dependencies in the root graph and subgraphs, leading to ambiguity as to which graph the dependency was bound to (see https://stackoverflow.com/questions/25953525/in-dagger-are-singletons-within-the-sub-graph-cached-or-will-they-always-be-recr)

### Dagger 2.0

Custom scopes allow you to create semantically clear scopes, but are functionally equivalent to applying `@Singleton` in Dagger 1.x.

    // Application level
    @Singleton
    @Component( modules = MyAppModule.class )
    public interface MyAppComponent {
        void inject(Application app);
    }

    @Module
    public class MyAppModule {

        @Singleton @Named(&quot;SingletonScope&quot;) @Provides
        StringBuilder provideStringBuilderSingletonScope() {
            return new StringBuilder(&quot;App&quot;);
        }
    }

---

    // Our custom scope
    @Scope public @interface PerActivity {}

---

    // Activity level
    @PerActivty
    @Component(
        dependencies = MyAppComponent.class,
        modules = MyActivityModule.class
    )
    public interface MyActivityComponent {
        void inject(Activity activity);
    }

    @Module
    public class MyActivityModule {

        @PerActivity @Named(&quot;ActivityScope&quot;) @Provides
        StringBuilder provideStringBuilderActivityScope() {
            return new StringBuilder(&quot;Activity&quot;);
        }

        @Name(&quot;Unscoped&quot;) @Provides
        StringBuilder provideStringBuilderUnscoped() {
            return new StringBuilder(&quot;Unscoped&quot;);
        }
    }

---

    // Finally, a sample Activity which gets injected
    public class MyActivity {

        private MyActivityComponent component;

        @Inject @Named(&quot;AppScope&quot;)
        StringBuilder appScope

        @Inject @Named(&quot;ActivityScope&quot;)
        StringBuilder activityScope1

        @Inject @Named(&quot;ActivityScope&quot;)
        StringBuilder activityScope2

        @Inject @Named(&quot;Unscoped&quot;)
        StringBuilder unscoped1

        @Inject @Named(&quot;Unscoped&quot;)
        StringBuilder unscoped2

        public void onCreate() {
            component = Dagger_MyActivityComponent.builder()
                .myApplicationComponent(App.getComponent())
                .build()
                .inject(this);

            appScope.append(&quot; &gt; Activity&quot;)
            appScope.build() // output matches &quot;App (&gt; Activity)+&quot; 

            activityScope1.append(&quot;123&quot;)
            activityScope1.build() // output: &quot;Activity123&quot;

            activityScope2.append(&quot;456&quot;)
            activityScope1.build() // output: &quot;Activity123456&quot;

            unscoped1.append(&quot;123&quot;)
            unscoped1.build() // output: &quot;Unscoped123&quot;

            unscoped2.append(&quot;456&quot;)
            unscoped2.build() // output: &quot;Unscoped456&quot;

        }

        public void onDestroy() {
            component = null;
        }

    }

The takeaway being that using `@PerActivity` communicates your *intention* regarding the lifecycle of this component, but ultimately you can use the component anywhere/anytime. Dagger&#39;s only promise is that, for a given component, scope annotated methods will return a single instance. I also assume Dagger 2 uses the scope annotation on the component to verify that modules only provide dependencies that are either in the same scope or non-scoped.

### In Summary

Dependencies are still either singleton or non-singleton, but `@Singleton` is now intended for application-level singleton instances and custom scopes are the preferred method for annotating singleton dependencies with a shorter lifecycle.

The developer is responsible for managing the lifecycle of components/dependencies by dropping references that are no longer needed and responsible for ensuring that components are only created once in the scope for which they are intended, but custom scope annotations make it easier to identify that scope.

## The $64k Question*

Is my understanding of Dagger 2 scopes and lifecycles correct?

*\* Not actually a $64&#39;000 question.*

What determines the lifecycle of a component (object graph) in Dagger 2?

I&#39;m trying to add Dagger2 to my project in Android Studio but I can&#39;t find proper dependency to paste in build.gradle. Could you help and send me the proper line?

Content Type	Original Author	Original Content on Stackoverflow
Question	MLProgrammer-CiM	View Question on Stackoverflow
Solution 1 - Android	mateusz.grzechocinski	View Answer on Stackoverflow
Solution 2 - Android	Kirill Boyarshinov	View Answer on Stackoverflow
Solution 3 - Android	lemuel	View Answer on Stackoverflow
Solution 4 - Android	Andrew Chen	View Answer on Stackoverflow

Dagger 2 examples

Android Problem Overview

Android Solutions

Solution 1 - Android

Solution 2 - Android

Solution 3 - Android

Solution 4 - Android

How to append to bytes in python 3

Path variables in Spring WebSockets @SendTo mapping

Attributions