Develop Reference

How to have some injections and some provided classes into a provided class

I'm getting started with Dagger 2 and trying to work out how to get #Inject and #Provides to work together well. It's easy to get everything working when the top-level class is injected. Like this:
class TopLevelClass {
#Inject
SecondaryClass1 class1;
private final SecondaryClass2 class2;
#Inject
TopLevelClass(SecondaryClass2 class2) {
this.class2 = class2;
}
}
#Module
class MyModule {
#Provides
SecondaryClass2 provideSecondaryClass2() {
return new SecondaryClass2();
}
}
However, everything stops working when I have to make a #Provides method for the top level class as well. Like this:
class TopLevelClass {
#Inject
SecondaryClass1 class1;
private final SecondaryClass2 class2;
TopLevelClass(SecondaryClass2 class2) {
this.class2 = class2;
}
}
#Module
class MyModule {
#Provides
TopLevelClass provideTopLevelClass(SecondaryClass2 class2) {
return new TopLevelClass(class2);
}
#Provides
SecondaryClass2 provideSecondaryClass2() {
return new SecondaryClass2();
}
}
With this example, I find that SecondaryClass1 never gets injected, so I get an NPE when I try to access it. Is there a different way that I'm supposed to do this for a provided top-level class?
P.S. I don't think it's relevant, but here's the component I'm using just in case it matters:
#Component(modules = {MyModule.class})
interface MyComponent {
TopLevelClass getTopLevelClass();
}
Thanks!

You have 2 options:
Make use of constructor injection and let Dagger create & inject the object (without any #Provides annotated method) The object will be ready to use without any need for code. This is where Dagger shines.
Create the object yourself and make sure it is correctly set up before returning it from the #Provides annotated method
I don't know why you would prefer the second option, or why you would even want to use field injection when you can make use of the constructor, but, as you found out, fields won't be injected if you manually construct the object. None of the generated Dagger code will run—you'll have to do this yourself.
One way that comes to mind is to request the component and then inject the object.
#Provides
TopLevelClass provideTopLevelClass(SecondaryClass2 class2, MyComponent component) {
TopLevelClass tlc = new TopLevelClass(class2);
component.inject(tlc);
return tlc;
}

Dagger 2 Object cannot be provided without an #Inject constructor

I'm fairly new to Dagger 2 and I have the following classes.
I have 2 modules:
DaoSessionModule
#Module
public class DaoSessionModule {
private DaoSession daoSession;
private Context context;
public DaoSessionModule(Context context) {
this.context = context;
if(daoSession == null) {
DaoMaster.DevOpenHelper helper = new DaoMaster.DevOpenHelper(this.context, "my_pocket");
Database db = helper.getWritableDb();
daoSession = new DaoMaster(db).newSession();
}
}
#Provides
LanguageDao providesLanguageDao() {
return daoSession.getLanguageDao();
}
#Provides
CategoryDao providesCategoryDao() {
return daoSession.getCategoryDao();
}
}
and GlobalPrefModule
#Module
public class GlobalPrefModule {
private GlobalPref globalPerf;
public GlobalPrefModule(GlobalPref globalPerf) {
this.globalPerf = globalPerf;
}
#Provides
public GlobalPref providesGlobalPref() {
return this.globalPerf;
}
}
and their components go as:
#Singleton
#Component(modules = {DaoSessionModule.class})
public interface DaoSessionComponent {
void inject(SplashActivity activity);
}
and
#Singleton
#Component(modules = {GlobalPrefModule.class })
public interface GlobalPrefComponent {
void inject(SplashActivity activity);
}
and I build both in my application class:
daoSessionComponent = DaggerDaoSessionComponent.builder()
.daoSessionModule(new DaoSessionModule(this))
.build();
globalPrefComponent = DaggerGlobalPrefComponent.builder()
.globalPrefModule(new GlobalPrefModule(new GlobalPref()))
.build();
and inject them in my splash activity:
public class SplashActivity extends BaseActivity {
#Inject
LanguageDao languageDao;
#Inject
GlobalPref globalPerf;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
initInjections();
}
private void initInjections() {
ZoopiApplication.app().getDaoSessionComponent().injectDao(this);
ZoopiApplication.app().getGlobalPrefComponent().injectGlobalPref(this);
}
}
now the problem I'm facing is that if I only inject DaoSession in my splash and comment out the GlobalPref impl it'll simply work but the moment I add GlobalPref along side with Daosession it fails to build and gives me the following error messages:
Error:(8, 52) error: cannot find symbol class DaggerDaoSessionComponent
Error:(9, 52) error: cannot find symbol class DaggerGlobalPrefComponent
Error:(16, 10) error: mypocket.com.zoopi.GlobalPref cannot be provided without an #Inject constructor or from an #Provides- or #Produces-annotated method.
mypocket.com.zoopi.GlobalPref is injected at
mypocket.com.zoopi.activities.SplashActivity.globalPerf
mypocket.com.zoopi.activities.SplashActivity is injected at
mypocket.com.zoopi.dagger.dagger2.components.DaoSessionComponent.injectDao(activity)
Error:(16, 10) error: mypocket.com.zoopi.models.LanguageDao cannot be provided without an #Inject constructor or from an #Provides- or #Produces-annotated method.
mypocket.com.zoopi.models.LanguageDao is injected at
mypocket.com.zoopi.activities.SplashActivity.languageDao
mypocket.com.zoopi.activities.SplashActivity is injected at
mypocket.com.zoopi.dagger.dagger2.components.GlobalPrefComponent.injectGlobalPref(activity)
and both generated classes DaggerDaoSessionComponent and DaggerGlobalPrefComponent are generated in the build foloder.
What could be the reason that I can't inject both objects into the same activity?

Injection has to be done from one component, and one component only.
It should be easy to see that the error message states that the object that can't be provided is the one you try to inject by the other component.
Dagger does not do "half" injections and one component has to inject all the fields. If partial injection would be possible you could end up with inconsistent states, since Dagger has no way of knowing how, when, or where you'd inject the rest of the fields. In short, it's just not possible. You'll have to use a single component.
but then I'll have many more modules soon and I don't know if it's a good idea to have one component to handle all modules...
That's okay. You will end up with quite a bunch of modules and possible quite a few components, depending on your setup. Make sure to use SubComponents where appropriate and you can even have modules include other modules, if you have big dependency groups split over multiple modules.

Mocking an injected field in unit tests

I have a Presenter class which uses a field injected through Dagger, it looks something like this:
public class RssListPresenter {
#Inject
RssService rssService; // <-- injected field
public RssListPresenter() {
setupDI();
}
private void setupDI() {
DaggerNetworkComponent.builder()
.networkModule(new NetworkModule())
.build()
.inject(this);
}
public void loadItems() {
Rss rss = rssService.getRssFeed()
// ....
}
}
Everything works fine. Now, I would like to unit test the RssListPresenter class. The question is how do I provide a mock RssService to the presenter?
Ofcourse I can add a new method setRssService(RssService rssService) to the presenter and use it to provide the mock from unit tests, but adding this method just for unit tests does not feel right. What would be the correct way to handle this?
For completeness here are the module and component declarations:
#Singleton
#Component(modules = NetworkModule.class)
public interface NetworkComponent {
void inject(RssListPresenter presenter);
}
#Module
public class NetworkModule {
#Provides
Retrofit provideRetrofit() {
// ...
}
#Provides
#Singleton
RssService providePcWorldRssService(Retrofit retrofit) {
return retrofit.create(RssService.class);
}
}

Property injection is like that is not so easy to test. In this case, Constructor injection is much better. Refactor your constructor to look like this:
private final RssService rssService;
#Inject
public RssListPresenter(RssService rssService) {
this.rssService = rssService;
}
Now you can test it easily:
//mocks
RssService mockRssService;
//system under test
RssListPresenter rssListPresenter;
#Before
public void setup() {
mockRssService = Mockito.mock(RssService.class);
rssListPresenter = new RssListPresenter(mockRssService);
}
You probably shouldn't be using DaggerNetworkComponent.inject(this) inside RssListPresenter. Instead you should be configuring dagger so that when it injects members into your top-level classes (Activity, Fragment, Service) it can access the object graph and create an instance of your RssPresenter.
Why only put injectors in Activity and Service and not in something like RssListPresenter? These are classes that are instantiated by the Android system and so you have no choice but to use injectors.
To clarify, Activity, Fragment etc. are ideal injection targets. RssListPresenter etc. are injected dependencies. You need to configure the dependency injection framework, dagger, so that it can provide the correct dependencies to inject into the injection targets.
So you will also need to write a #Provides method for RssListPresenter
#Provides provideRssListPresenter(RssService rssService) {
return new RssListPresenteR(rssService);
}

Your class violates some of the S.O.L.I.D principles, and this makes it very difficult to unit test it. Your class for sure violats the SRP(Single Responsability Principle) as it has more than one reason to change. There is also a possible Dependency Inversion violation.
I advice to rethink the model of the classes, so that each of them performs a specific function, and has one reason to change.

Dagger 2 on Android #Singleton annotated class not being injected

I am currently trying to integrate Dagger 2 into an Android application. My project setup is as follows:
library
app (depends on library)
In my library project I defined a class that I'll later inject into other classes that need it (Activities and regular classes) in the library as well as the app project.
#Singleton
public class MyManager{
#Inject
public MyManager(){
//Do some initializing
}
}
Now - for instance in my Fragments or Activities or regular classes I'd inject the above Singleton as follows:
public class SomeClass{
#Inject
MyManager myManager;
}
Or so I thought, because in practice myManager is always null. And apparently it's constructor is never called either, so I guess I must be missing something configuration-wise? Or maybe I misunderstood the documentation and it's not meant to work this way at all? The purpose of MyManager class is to be an application-wide accessible component-accumulating entity - that's why I went for the #Singleton.
UPDATE
To avoid confusion: I mentioned my having components somewhere in a comment I think - this refers to components in the sense of "component based design" and has nothing to do with dagger. The dagger-based code I have is all listed above - there is nothing else related to dagger in my code.
When I started adding #Component I had some compiler issues, because my dagger2 was not setup properly - check out this really helpful thread on how to setup dagger2 correctly: https://stackoverflow.com/a/29943394/1041533
UPDATE 2
Here is my updated code, based on G. Lombard's suggestions - I changed the code as follows - the original Singleton is in the library project:
#Singleton
public class MyManager{
#Inject
public MyManager(){
//Do some initializing
}
}
Also in the library project is the bootstrap class:
#Singleton
#Component
public interface Bootstrap {
void initialize(Activity activity);
}
Then I use the above Bootstrap class in my activity (in my concrete app, NOT in the library project! I do however also have Classes/Activities in the library that'll access Bootstrap to inject MyManager):
public class MyActivity extends Activity{
#Inject
MyManager manager;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
//DONT DO THIS !!! AS EXPLAINED BY EpicPandaForce
DaggerBootstrap.create().initialize(this);
}
}
But even after this line:
DaggerBootstrap.create().initialize(this);
the manager instance is still null, i.e. not injected.
I just found this: https://stackoverflow.com/a/29326023/1041533
Which if I don't misread, implies I need to specify every single class in the Bootstrap class that will use #Inject to have stuff injected. Sadly - this is not an option, as I have more than 40 classes and activities for which I'd have to do that.
Meaning my Bootstrap interface apparently would have to look something like this:
#Singleton
#Component
public interface Bootstrap {
void initialize(ActivityA activity);
void initialize(ActivityB activity);
void initialize(ActivityC activity);
void initialize(ActivityD activity);
void initialize(ActivityE activity);
void initialize(ActivityF activity);
//and so on and so forth...
}
If the above is true, that would not be worth it for my use case. Plus: Seems there is no compile-time check, if I forgot to specify one of my 40+ classes here? It just wont work - i.e. crash the app at runtime.

You're making a mistake in that you are using
DaggerBootstrap.create().initialize(this);
in your Activity, as scopes are not shared across multiple component instances. What I recommend is using a custom application class
public class CustomApplication extends Application {
#Override
public void onCreate() {
super.onCreate();
Bootstrap.INSTANCE.setup();
}
}
#Component
#Singleton
public interface _Bootstrap {
void initialize(ActivityA activityA);
//void initiali...
}
public enum Bootstrap {
INSTANCE;
private _Bootstrap bootstrap;
void setup() {
bootstrap = Dagger_Bootstrap.create();
}
public _Bootstrap getBootstrap() {
return bootstrap;
}
}
Then you could call it as
Bootstrap.INSTANCE.getBootstrap().initialize(this);
This way, you share the component across your classes. I personally named Bootstrap as injector, and _Bootstrap as ApplicationComponent, so it looks like this:
Injector.INSTANCE.getApplicationComponent().inject(this);
But that's just my typical setup. Names don't really matter.
EDIT: To your last question, you can solve this by subscoping and component dependencies.
Your library project should be able to see only the library classes, correct? In that case, all you do is
#Scope
#Retention(RetentionPolicy.RUNTIME)
public #interface LibraryScope {
}
#Component(modules={LibraryModule.class})
#LibraryScope
public interface LibraryComponent {
LibraryClass libraryClass(); //provision method for `MyManager`
}
#Module
public class LibraryModule {
#LibraryScope
#Provides
public LibraryClass libraryClass() { //in your example, LibraryClass is `MyManager`
return new LibraryClass(); //this is instantiation of `MyManager`
}
}
public enum LibraryBootstrap {
INSTANCE;
private LibraryComponent libraryComponent;
static {
INSTANCE.libraryComponent = DaggerLibraryComponent.create();
}
public LibraryComponent getLibraryComponent() {
return libraryComponent;
}
}
#Scope
#Retention(RetentionPolicy.RUNTIME)
public #interface ApplicationScope {
}
#Component(dependencies={LibraryComponent.class}, modules={AdditionalAppModule.class})
#ApplicationScope
public interface ApplicationComponent extends LibraryComponent {
AdditionalAppClass additionalAppClass();
void inject(InjectableAppClass1 injectableAppClass1);
void inject(InjectableAppClass2 injectableAppClass2);
void inject(InjectableAppClass3 injectableAppClass3);
}
#Module
public class AdditionalAppModule {
#ApplicationScope
#Provides
public AdditionalAppClass additionalAppClass() { //something your app shares as a dependency, and not the library
return new AdditionalAppClass();
}
}
public enum ApplicationBootstrap {
INSTANCE;
private ApplicationComponent applicationComponent;
void setup() {
this.applicationComponent = DaggerApplicationComponent.builder()
.libraryComponent(LibraryBootstrap.INSTANCE.getLibraryComponent())
.build();
}
public ApplicationComponent getApplicationComponent() {
return applicationComponent;
}
}
Then
#Inject
LibraryClass libraryClass; //MyManager myManager;
...
ApplicationBootstrap.INSTANCE.getApplicationComponent().inject(this);

It's hard to say what your problem was, since you didn't show what your Component looks like and whether you have multiple components etc.
Assuming this logical structure:
/app
MainComponent
SomeClass // where MyManager is to be injected
MainActivity // where SomeClass is to be injected
/library
LibraryComponent
MyManager // Singleton
Then your classes as listed would inject correctly with the following configuration:
#Singleton
#Component
public interface LibraryComponent {
MyManager getMyManager();
}
and the app-level component to inject dependencies into the activity:
#ActivityScope
#Component(dependencies = LibraryComponent.class)
public interface MainComponent {
void inject(MainActivity mainActivity);
}
Note that MainComponent depends on LibraryComponent, but because the latter has singleton scope, you need to define a scope for the other one too, which I was I used the "activity scope" here. (Or you could also just make the MainComponent a singleton and get rid of the LibraryComponent completely if that suits your needs.)
Finally it's all injected into the activity like this:
#Inject
SomeClass someClass;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
DaggerMainComponent.builder()
.libraryComponent(DaggerLibraryComponent.create())
.build()
.inject(this);
someClass.doSomething();
}
I've put a working sample here on GitHub
Update 1:
If I understand your setup correctly, you've so far only used the #Singleton and #Inject annotations on the two classes listed (MyManager and SomeClass), and there is no other Dagger-related code in your project.
In that case, the reason your MyManager isn't getting injected, is because Dagger doesn't know how to provide/instantiate the dependencies. This is where the "components" come in that I mentioned above. Without any Dagger 2 components (interface or abstract class annotated with #Component), your dependencies won't get injected automatically.
I don't know if you have experience with Dependency Injection concepts, but assuming you don't, I'll step through the minimum basics you'll need to understand to get your MyManager injected into SomeClass:
First: when you use DI, you need to understand the difference between "newables" and "injectables". This blogpost by Misko Hevery explains the details.
This means, you can't new up your SomeClass. This won't work:
mSomeClass = new SomeClass();
Because if you did that (say in an activity or fragment), Dagger will have no idea that you expected a dependency to get injected into SomeClass and it has no opportunity to inject anything.
In order for its dependencies to get injected, you have to instantiate (or inject) SomeClass itself through Dagger too.
In other words, say in your Activity where SomeClass is used, you'll need:
#Inject
SomeClass mSomeClass;
Next, you need a Dagger component to perform the actual injection. To create a component, you create an interface with a method that takes your root object (say MainActivity) as argument, e.g.:
#Singleton
#Component
public interface Bootstrap {
void initialize(MainActivity activity);
}
Now when you build your project, Dagger 2 generates a class called DaggerBootstrap that implements this interface. You use this generated class to perform the injection, say in your activity's onCreate:
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
DaggerBootstrap.create().initialize(this);
mSomeClass.doSomething();
}
I believe this generated component is the key part you're missing. Full code for above here.
Some useful Dagger 2 resources:
the official Dagger 2 guide
reddit page with lots of links
Update 2:
Seems like the final missing piece of the puzzle was that your component provided an inject method for the Activity base class, but not for your actual concrete activity.
Unfortunately Dagger 2 requires an inject method for each activity or other class you want to inject into.
As you mentioned, this will be annoying when you have many different activities in your app. There some possible workarounds for this, search for "dagger 2 inject base class", for example this suggestion by #EpicPandaForce: Dagger 2 base class injections
Also note, as pointed out by #EpicPandaForce in the comments, that in my simplistic example I called DaggerLibraryComponent.create() every time which is probably not what you want, since that component is supposed to provide your singletons, so you're probably better off getting the existing instance from somewhere else such as from your Application instance.

Module depending on another module in Dagger

I'm trying to use Dagger to do Dependency Injection on an app that I'm building, and running into trouble constructing proper DAGs when I have one package's Module depending on values provided by the Injector (presumably provided by another Module).
If I have a simple module for some configurable variables (that I might want to swap out for testing environments, for example)
#Module(
injects = DependentModule.class,
)
public class ConfigModule {
#Provides #Named("ConfigOption") String provideConfigOption() {
return "This Module's configurable option!";
}
}
and another module depends on it, e.g.
#Module(
injects = {
TopLevelClass.class
}
)
public class DependentModule {
#Inject #Named("ConfigOption") String configOption;
public DependentModule() {
ObjectGraph.create(this).inject(this);
doSomethingWithConfig(configOption);
}
#Provides #Singleton UsefulValue provideUsefulValue() {
// Whatever this module needs to do...
}
}
The line where I try to bootstrap the injection in the constructor fails, and it complains that I haven't specified an explicit injects line in a proper module.
Through trial-and-error I see this goes away if in #Module I add a line include = ConfigModule.class, but this strikes me as semantically wrong, since a) the DAG I'll be creating will now include the values of both modules, rather than just one, and b) it defeats the purpose/flexibility of DI in the first place to link a specific Module rather than simply let Dagger inject the appropriate value.
I'm presuming I shouldn't be creating an Object Graph with this only to inject into it? But then I run into the issue of not linking a specific Module...
Succinctly:
What is the 'proper' way to Inject values into one Modules that may be provided from other Modules? Here I'm using field injection, but my experiments with constructor injection have also resulted in a lot of failure.
Relatedly, when is it appropriate to use addsTo vs. includes?
Thanks :)

You don't need to do any of injection (field or constructor) in one module from another explicitly. Just use addsTo and includes.
includes allows to add modules to another and use everything they provide. Example:
#Module()
public class ModuleA {
#Provides #Named("ValueA") String provideValueA() {
return "This is ValueA";
}
}
#Module(
includes = ModuleA.class
)
public class ModuleB {
// ValueA comes from ModuleA
#Provides #Named("ValueB") String provideValueB(#Named("ValueA") String valueA) {
return valueA + " and ValueB";
}
}
addsTo is used with ObjectGraph.plus(Object... modules). When graph is already created and contains some modules (e.g. in Application class), you can create new graph (e.g. in Activity) using plus. Example:
#Module()
public class ApplicationModule {
#Provides #Named("ValueA") String provideValueA() {
return "This is ValueA";
}
}
#Module(
addsTo = ApplicationModule.class
)
public class ActivityModule {
// ValueA comes from ApplicationModule
#Provides #Named("ValueB") String provideValueB(#Named("ValueA") String valueA) {
return valueA + " and ValueB";
}
}
public class DemoApplication extends Application {
private ObjectGraph graph;
#Override public void onCreate() {
super.onCreate();
graph = ObjectGraph.create(getModules().toArray());
}
protected List<Object> getModules() {
return Arrays.asList(
new ApplicationModule()
);
}
public void inject(Object object) {
graph.inject(object);
}
public ObjectGraph getObjectGraph() {
return graph;
}
}
public class DemoActivity extends Activity {
private ObjectGraph activityGraph;
#Override protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
// Create the activity graph by .plus-ing our modules onto the application graph.
DemoApplication application = (DemoApplication) getApplication();
activityGraph = application.getApplicationGraph().plus(new ActivityModule());
// Inject ourselves so subclasses will have dependencies fulfilled when this method returns.
activityGraph.inject(this);
}
#Override protected void onDestroy() {
// Eagerly clear the reference to the activity graph to allow it to be garbage collected as
// soon as possible.
activityGraph = null;
super.onDestroy();
}
}
Also you can check this example to create scopes of graphs.