I'm having a project based on Dagger 2 which consists of two modules. The core module includes some interfaces and some classes that have member injections declared for these interfaces.
The actual implementations of these interfaces are included in the second module which is an Android project. So, naturally the provide methods for these are included in the Android project.
Dagger will complain during compilation about not knowing how to inject these in the core module.
Any thoughts on how to achieve this without using constructor injections?
In short, I just tried this, and it works. Be sure to check the exact error messages and make sure you are providing these interfaces and #Inject annotations are present.
There is probably just some wrong named interface or a missing annotation. Following up is a full sample using your described architecture that is compiling just fine. The issue you are currently experiencing is probably the one described in the last part of this post. If possible, you should go with the first solution though and just add those annotations.
The library
For reproducability this sample has minimalist models. First, the interface needed by my class in the library module:
public interface MyInterface {
}
Here is my class that needs that interface. Make sure to declare it in the constructor and provide the #Inject annotation!
#MyScope // be sure to add scopes in your class if you use constructor injection!
public class MyClassUsingMyInterface {
private MyInterface mMyInterface;
#Inject
public MyClassUsingMyInterface(MyInterface myInterface) {
mMyInterface = myInterface;
}
}
The idea is that the interface will be implemented by the app using MyClassUsingMyInterface and provided by dagger. The code is nicely decoupled, and my awesome library with not so many features is complete.
The application
Here need to supply the actual coupling. This means to get MyClassUsingMyInterface we have to make sure we can supply MyInterface. Let's start with the module supplying that:
#Module
public class MyModule {
#Provides
MyInterface providesMyInterface() {
return new MyInterface() {
// my super awesome implementation. MIT license applies.
};
}
}
And to actually use this, we provide a component that can inject into MyTestInjectedClass that is going to need MyClassUsingMyInterface.
#Component(modules = MyModule.class)
public interface MyComponent {
void inject(MyTestInjectedClass testClass);
}
Now we have a way to provide the requested interface. We declared that interface needed by the library class in a constructor marked with #Inject. Now I want a class that requires my awesome library class to use. And I want to inject it with dagger.
public class MyTestInjectedClass {
#Inject
MyClassUsingMyInterface mMyClassUsingMyInterface;
void onStart() {
DaggerMyComponent.create().inject(this);
}
}
Now we hit compile...and dagger will create all the factories needed.
Inject Libraries you can not modify
To just provide the full scale of dagger, this sample could also have been without actual access to the source code of the library. If there is no #Inject annotation dagger will have a hard time creating the object. Notice the missing annotation:
public class MyClassUsingMyInterface {
private MyInterface mMyInterface;
public MyClassUsingMyInterface(MyInterface myInterface) {
mMyInterface = myInterface;
}
}
In that case we have to manually provide the class. The module would be needed to be modified like the following:
#Module
public class MyModule {
#Provides
MyInterface providesMyInterface() {
return new MyInterface() {
};
}
#Provides
MyClassUsingMyInterface providesMyClass(MyInterface myInterface) {
return new MyClassUsingMyInterface(myInterface);
}
}
This introduces more code for us to write, but will make those classes available that you can not modify.
Related
My team owns a library that provides components that must be referencable by code that consumes the library. Some of our consumers use Spring to instantiate their apps; others use Guice. We'd like some feedback on best-practices on how to provide these components. Two options that present themselves are:
Have our library provide a Spring Configuration that consumers can #Import, and a Guice Module that they can install.
Have our library provide a ComponentProvider singleton, which provides methods to fetch the relevant components the library provides.
Quick sketches of what these would look like:
Present in both approaches
// In their code
#AllArgsConstructor(onConstructor = #__(#Inject))
public class ConsumingClass {
private final FooDependency foo;
...
}
First approach
// In our code
#Configuration
public class LibraryConfiguration {
#Bean public FooDependency foo() {...}
...
}
---
public class LibraryModule extends AbstractModule {
#Provides FooDependency foo() {...}
...
}
========================
========================
// In their code
#Configuration
#Import(LibraryConfiguration.java)
public class ConsumerConfiguration {
// Whatever initiation logic they want - but, crucially, does
// *not* need to define a FooDependency
...
}
---
// *OR*
public class ConsumerModule extends AbstractModule {
#Override
public void configure() {
// Or, simply specify LibraryModule when creating the injector
install(new LibraryModule());
...
// As above, no requirement to define a FooDependency
}
}
Second approach
// In our code
public class LibraryProvider {
public static final INSTANCE = buildInstance();
private static LibraryProvider buildInstance() {...}
private static LibraryProvider getInstance() {return INSTANCE;}
}
========================
========================
// In their code
#Configuration
public class ConsumerConfiguration {
#Bean public FooDependency foo() {
return LibraryProvider.getInstance().getFoo();
}
...
}
// or equivalent for Guice
Is there an accepted Best Practice for this situation? If not, what are some pros and cons of each, or of another option I haven't yet thought of? The first approach has the advantage that consumers don't need to write any code to initialize dependencies, and that DI frameworks can override dependencies (e.g. with mocked dependencies for testing); whereas the second approach has the advantage of being DI-framework agnostic (if a new consumer wanted to use Dagger to instantiate their app, for instance, we wouldn't need to change the library at all)
I think the first option is better. If your library has inter-dependencies between beans then the code of #Configuration in case of spring in the second approach) will be:
Fragile (what if application doesn't know that a certain bean should be created)
Duplicated - this code will appear in each and every consumer's module
When the new version of your library gets released and a consumer wants to upgrade- there might be changes in consumer's configuration ( the lib might expose a new bean, deprecate or even remove some old stuff, etc.)
One small suggestion:
You can use Spring factories and then you don't even need to make an #Import in case of spring boot. just add a maven dependency and it will load the configuration automatically.
Now, make sure that you work correctly with dependencies in case of that approach.
Since you code will include both spring and Juice dependent code, you'll add dependencies on both for your maven/gradle module of the library. This means, that consumer that uses, say, guice, will get all the spring stuff because of your library. There are many ways to overcome this issue depending on the build system of your choice, just want wanted to bring it up
I am having problems injecting a generic type interface. Not sure how to do this or google it since I don't know the exact terms to search for. Sorry if i'm completely wrong just getting started with dagger.
Basically I have a use case class
public class LoadConversations<C extends IConversation>
extends UseCase<List<C>, LoadConversations.Type> {
private final IConversationRepository<C> messageRepository;
#Inject LoadConversations(#NonNull IConversationRepository<C> messageRepository) {
this.messageRepository = messageRepository;
}
....
public enum Type {
ALL, NEWER, OLDER
}
}
With IConversationRepository being an interface.
public interface IConversationRepository<C extends IConversation> {
Observable<List<C>> conversations(LoadConversations.Type params);
}
IConversation being a blank interface and ConversationModule where i provide the IConversationRepository.
Im having problems injecting with the following code. Am i missing something or doing something completey wrong. Thanks in advance.
Trying to provide as follows:
#Provides IConversationRepository<Conversation> provideConversationRepository(
ConversationRepository conversationRepository) {
return conversationRepository;
}
And I'm trying to inject this to my presenter as
private final LoadConversations<Conversation> loadConversations;
#Inject public ConversationListPresenter(LoadConversations<Conversation> loadConversations) {
this.loadConversations = loadConversations;
}
Implementation of ConversationRepository
public class ConversationRepository implements IConversationRepository<Conversation> {
#Override public Observable<List<Conversation>> conversations(LoadConversations.Type params) {
....
}
}
Error Log:
Error:(15, 10) error: com.rbttalk.android.data.repository.ConversationRepository cannot be provided without an #Inject constructor or from an #Provides-annotated method.
com.rbttalk.android.data.repository.ConversationRepository is injected at
com.rbttalk.android.di.module.sub_modules.ConversationModule.provideConversationRepository(conversationRepository)
com.rbttalk.android.domain.repository.IConversationRepository<com.rbttalk.android.domain.models.Conversation> is injected at
com.rbttalk.android.domain.usecase.conversation.LoadConversations.<init>(arg0, …)
com.rbttalk.android.domain.usecase.conversation.LoadConversations<com.rbttalk.android.domain.models.Conversation> is injected at
com.rbttalk.android.ui.main.conversation.ConversationListPresenter.<init>(loadConversations)
com.rbttalk.android.ui.main.conversation.ConversationListPresenter is injected at
com.rbttalk.android.ui.main.conversation.ConversationListFragment.userListPresenter
com.rbttalk.android.ui.main.conversation.ConversationListFragment is injected at
com.rbttalk.android.di.component.ConversationComponent.inject(conversationListFragment)
You're very close! The error message says it all:
com.rbttalk.android.data.repository.ConversationRepository cannot be provided without an #Inject constructor or from an #Provides-annotated method.
Note that this is not IConversationRepository; you've provided a binding for that with your #Provides method (which you can eventually consider converting to a #Binds method). However, that #Provides method has a parameter, ConversationRepository, which effectively asks Dagger to create an instance of that concrete ConversationRepository type for you. You've made that binding correctly, but now Dagger needs to instantiate ConversationRepository for you, and it simply doesn't know how.
You'll need to create an #Inject-annotated constructor for ConversationRepository using the annotation type javax.inject.Inject, even if it just looks like this:
#Inject ConversationRepository() {}
This allows Dagger to know that yes, it is safe to call that constructor. (This differs from Guice, which was willing to call a public parameterless constructor including the default constructor provided by Java.) Though you are welcome to accept injector-provided parameters in that annotated constructor (which might be nice if your repository has dependencies, because then you can keep the fields final), you may also choose to simply annotate some fields with #Inject and let the injector populate those after creation.
I'm starting to use Dagger 2 in an application I'm developing but I have some questions about how Dagger 2 works.
I get the all the logic behind the #Provides methods and the #Inject annotation for initialising your dependencies, but the #Inject annotation to class constructors kind of bugs my mind.
For example:
Im my app, I have one module defined, the ContextModule, to retrieve the context of my application:
ContextModule.java
#Module
public class ContextModule {
private final Context context;
public ContextModule(Context context) {
this.context = context;
}
#Provides
public Context context() {
return this.context;
}
}
This module is used by my BaseActivityComponent:
BaseActivityComponent.java
#BaseActivityScope
#Component(modules = ContextModule.class)
public interface BaseActivityComponent {
void injectBaseActivity(BaseActivity baseActivity);
}
So far so good.. then I have an AuthController class, that depends on the context and I want to inject it in my BaseActivity. So in my AuthControllers.class I have something like:
public class AuthController {
private Context context;
#Inject
public AuthController(Context context) {
this.context = context;
}
public void auth() {
// DO STUFF WITH CONTEXT
}
}
And I inject it in my BaseActivity like:
public class BaseActivity extends AppCompatActivity {
#Inject
AuthController authController;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
BaseActivityComponent component = DaggerBaseActivityComponent.builder()
.contextModule(new ContextModule(this))
.build();
component.injectBaseActivity(this);
authController.auth();
}
}
Now my question is, how does dagger knows that my AuthControllers is a dependency for BaseActivity? Just by declaring
#Inject
AuthController authController;
it's like the same thing as if I created a ControllerModule like:
#Module(includes = ContextModule.class)
public class ControllerModule {
#Provides
AuthController authController(Context context) {
return new AuthController(context);
}
}
And then in my BaseActivityComponent I would add my AuthController getter and change my dependency module to ControllersModule:
#BaseActivityScope
#Component(modules = ControllersModule.class)
public interface BaseActivityComponent {
void injectBaseActivity(BaseActivity baseActivity);
AuthController getAuthController();
}
When I call injectBaseActivity(this) it "tells" dagger that all #Inject annotations are dependencies of my class, and then it searchers my project for #Inject annotated constructors that matches that type?
I thought a good thing about Dagger 2 is that the Module files could be used as a "documentation" of my dependencies three. But if just add #Inject in all the constructors I have control of, couldn't it get a little confusing in the future, since you don't know what actually depends on what? (I mean, you know what depends on what, you just have to browse a lot of files to really find out)
Is there any best practices for when using #Inject annotations in constructors or when to add the #Provides method in Modules files?
I get that using #Inject in constructor I don't need to change the constructor definition in my Module file, but is there any downside?
Thanks.
When I call injectBaseActivity(this) it "tells" dagger that all #Inject annotations are dependencies of my class, and then it searches my project for #Inject annotated constructors that matches that type?
Exactly. But it's not done when you call injectBaseActivity, but it all happens during compile time. This is one way of annotation processing (another makes use of reflection at runtime).
When you build your project the dagger-annotation-processor you include (as a dependency)in your build.gradle file gets called with a list of all your fields, classes, etc annotated by the #Inject annotation and builds a dependency graph with it. It then resolves the graph, generating source code that provides all the dependencies for the items on the graph.
injectBaseActivity just executes the code which was generated before, and assigns all the dependencies to your object. It is proper source code, which you can read, and debug.
The reason this is a compile step—simply put—is performance and validation. (e.g. If you have some dependency cycle, you get a compile error)
how does dagger knows that my AuthControllers is a dependency for BaseActivity?
#Inject
AuthController authController;
By annotating the field #Inject dagger knows you want an AuthController. So far so good. Now dagger will look for some means to provide the controller, looking for it within the component, the components dependencies, and the components modules. It will also look whether the class can be supplied on its own, because it knows about its constructor.
How does dagger know about the objects constructor if you don't include it in any module?
#Inject
public AuthController(Context context) { /**/ }
By annotating the constructor with inject you also told dagger that there is a class called AuthController and you need a context for it to be instantiated. It is basically the same as adding it to your module.
A module #Provides method should be used if you don't have the source code to just add the #Inject annotation to the constructor, or if the object needs further initialization. Or in your case...
[...]the Module files could be used as a "documentation" of my dependencies tree [...]
Yes, of course you could do that. But as your project grows you will have to maintain a lot of unnecessary code, since the same could have been done with a simple annotation on the constructor.
Is there any best practices for when using #Inject annotations in constructors or when to add the #Provides method in Modules files?
If you want to provide different versions for a different context (e.g. implementing an interface in 2 different ways) there is also the #Binds annotation that tells dagger which class you wish to provide as implementation.
Other than that I believe you should always use constructor injection when possible. If something changes you don't have to touch any other parts of your code, and it is just less code that you write, and hence less places where you could include a bug.
Also Dagger can and does optimize a lot by knowing more, and if you implement unnecessary code it will have to work with the overhead you introduced
Of course in the end it is all up to what you think is best. After all it is you that has to work with your code ;)
I have a project that provides an interface, let's call it IImplementMe, which i want to inject into my project. This interface will be implemented by various producers, so I need to inject all implementations. I am trying to use TypeLiteral for this.
Here is the code of the producer :
#Singleton
public class SomeImplementation implements IImplementMe {
private final String value;
#Inject
public SomeImplementation(final SomeOtherConfig configuration) {
this.value= configuration.getValue();
}
#Override
public String getValue() {
return value;
}
}
And in my registry class I have register(IImplementMe.class).to(SomeImplementation.class);
Then, in my project I inject it like this :
#Inject
public SomeEndpoint(final List<IImplementMe> implementations){
///
}
and i bind it like
private static class MarketDataSetTypeLiteral extends TypeLiteral<List<IImplementMe>> {
}
bind(new MarketDataSetTypeLiteral()).toRegistry();
I made sure my SomeIMplementation constructor gets called, but in my endpoint the List is empty, so no implementation is provided. I'm using guice for injection. Any ideas ?
LE: It turns out that the provided implementation is created after my endpoint class is created (at creation time it injects a reference of an empty list). Later in the lifecycle the reference is updated with the implementation, so I actually have access to it after guice does it's stuff.
I'm guessing it's due to the maven dependencies, and how guice handles the instantiations. Since the producer must have a dependency on my project, I guess it makes sense it gets instantiated last, thus causing my initial problem.
You are looking for multibindings -> https://github.com/google/guice/wiki/Multibindings
public class IImplementMeModule extends AbstractModule {
public void configure() {
Multibinder< IImplementMe > uriBinder = Multibinder.newSetBinder(binder(), IImplementMe.class);
uriBinder.addBinding().to(SomeImplementationOfIImplementMe.class);
uriBinder.addBinding().to(AnotherImplementationOfIImplementMe.class);
... // bind plugin dependencies, such as our Flickr API key
}
}
Then you can inject the set of IImplemetnMe as following
#Inject TweetPrettifier(Set<IImplemetnMe> implementations)
I would suggest you to have a look at MapBindings which allows you provide keys for each implementation and then you will be able to inject your bindings as a Map
Let's say I have the following classes and dagger module
public class Base implements IBase {
private IDependency dependency; //IDependency is an interface
Base(IDependency dependency) {
this.dependency = dependency
}
}
public class SubClass extends Base implements ISubclass {
Base(IDependency dependency) {
super(dependency)
}
}
#Module
public class MyModule {
// Let's assume some other class use SubClass and requires this
#Provides
ISubclass providesSubclass(IDependency dependency) {
return new SubClass(dependency);
}
}
If I add a new parameter to Base constructor, I'll have to go to MyModule and modify provides method to include this new parameter (besides obviusly chaging Base and Subclass constuctors). It seems to me that using propery injection I don't have this problem since I'm not using any constructor.
My feeling is that I might be doing something wrong or I have some concept wrong. I prefer constructor injection over property injection but right now I have to add a constructor parameter to a base class used by 40 other classes and not only I have to modify those 40 classes constructors, I also have to modify modules to reflect new constructors parameters.
Am I missing something? Am I correct if I say that doing constructor injection I'll write much more less code and maintenance will be easier?
Yes, you are missing some awesome feature: You can still use constructor injection in this case! And you don't even have to write it yourself.
If all of the dependencies can be provided, dagger can and will create the object for you. Given that you can provide IDependency you just need to modify your code like the following:
public class SubClass extends Base implements ISubclass {
#Inject // Don't forget the annotation!
public Base(IDependency dependency) {
super(dependency)
}
}
#Module
public class MyModule {
#Provides
ISubclass providesSubclass(SubClass subclass) {
return subclass;
}
}
You provide the interface, yet you depend on your implementation to provide it. Dagger will resolve this, and you can merrily add as many parameters to the constructor as you like. (Apart from the obvious changes to the actual constructors you already pointed out)
Don't forget the #Inject annotation!