I have an unscoped binding inside the appModule and the same class as constructor injected using the Singleton scope. when I add a declaration inside the appComponent for Foo, the generated code picks up the module binding without any DoubleCheck i.e unscoped binding over the constructor injected Singleton binding why is it so?
#Module
public class AppModule {
#Provides
public Foo provideFoo() {
return new Foo();
}
}
#Component(module = AppModule.class)
#Singleton
public interface AppComponent {
Foo getFoo();
}
#Singleton
class Foo #Inject constructor(){
//..
}
There is some hierarchy in how dependencies are provided, I haven't found documentation on this yet, but I ran into the same thing as well. If I recall it correctly from my testing, the hierarchy of where Dagger tries to get the dependency from is the following:
Bound instances (via component builder methods; i.e. #BindsInstance)
Module provision
Constructor injected classes
Somewhere in this list provisioned dependencies should probably also be included (provisioned from a parent component your component has a dependency on), but I dont know where it would be then in the hierarchy.
Usually there is no need to provide the same dependency in multiple ways, why would you both want to provide the dependency via a Module and via constructor injection? If there are multiple dependencies, but they live in a different scope, try using different scopes instead of just the singleton one.
I can think of one reason where you want to use this mechanic, and thats when you normally want a certain dependency to be provided via either constructor or module injection, but specifically for a test build, you want to overwrite that dependency with a different dependency by changing how the component is composed in a test build (i.e. then changing the DaggerComponent so it requires a #BindsInstance method to overwrite the default dependency with a test dependency).
Related
Hilt is not supportting non epmty constructor modules. If we need to migrate partially to Hilt from dagger , how we can inject dependencies from legacy dagger modules having non empty constrctors to hilt components such as HiltViewModel.
// Legacy Dagger module
#Module
public class DaggerModule {
private final Boolean customBoolean;
DaggerModule(Boolean customBoolean) {
this.customBoolean = customBoolean;
}
#Provides
#Singleton
CustomClass provideCustomClass() {
return CustomClass(customBoolean);
}
}
#Module
public class AnotherDaggerModule {
#Provides
#Singleton
AnotherClassDepndsOnCustomClass provideAnotherClass(CustomClass customClass) {
return AnotherClassDepndsOnCustomClass(customClass);
}
}
// Migrated Hilt module
#HiltViewModel
class HiltViewModel #Inject constructor(
private val anotherClass: AnotherClassDepndsOnCustomClass
) : ViewModel() {
...
}
Since we are not using components to pass some custom parameters while initialising modules, is there any solution which I'm not aware already exists?
While running the app, the app crashing with error DaggerModule must be set.
You'll need to refactor.
The documentation on Migrating to Hilt describes this case under the heading "Handling Component Arguments", since instantiable modules would otherwise be treated as component arguments passed through a Builder or Factory:
Hilt components cannot take component arguments because the initialization of the component is hidden from users. [...]
If your component has any other arguments either through module instances passed to the builder or #BindsInstance, read this section on handling those. Once you handle those, you can just remove your #Component.Builder interface as it will be unused.
Under "Component arguments" the Hilt documentation confirms that a refactor is required:
Because component instantiation is hidden when using Hilt, it is not possible to add in your own component arguments with either module instances or #BindsInstance calls. If you have these in your component, you’ll need to refactor your code away from using these.
You can consider some of these structures:
Replacement module / subclassing Modules
In your example, you might need to create a replacement Module that provides a binding for CustomClass. This might be as straightforward as subclassing the Module and providing a public no-arg constructor that provides the super(value) constructor call your module needs. If your Module would only ever get a single value in your graph (but might get a different value in a separate application), then this might be enough.
#Module
public class AdaptedDaggerModule extends DaggerModule {
AdaptedDaggerModule() {
super(true);
}
}
Note that module subclasses are somewhat limited in utility, and should not be used for testing overrides.
Custom subcomponents
However, you also wrote "components are created in respective modules where we need to use" in a comment, and you can continue doing so using custom subcomponents in Hilt, with more comprehensive documentation in javadoc or the main Dagger subcomponent documentation. Because you would create this component through an explicit call to a Builder or Factory, you could provide the Module instance there. Subcomponents inherit bindings from their parent components, so you could avoid specifying your entire list of Modules.
Note that doing this as a subcomponent is mostly valuable when you have a dense tree with multiple references to the instance you're providing in the constructor. If this is simply a matter of combining graph-based constructor arguments with one-off constructor arguments, assisted injection is probably a better option.
/** Subcomponents are usually declared on modules. You can also reuse one you have. */
#Module(subcomponents={YourSubcomponent.class})
public interface IncludeThisInYourHiltModuleList {}
#Subcomponent(modules={DaggerModule.class, AnotherDaggerModule.class})
public interface YourSubcomponent {
AnotherClassDepndsOnCustomClass anotherClass();
#Subcomponent.Builder
interface Builder {
Builder daggerModule(DaggerModule daggerModule); // arbitrary name
YourSubcomponent build(); // arbitrary name
}
}
#HiltViewModel
class HiltViewModel #Inject constructor(
private val yourSubcomponentBuilder: YourSubcomponent.Builder
) : ViewModel() {
fun yourMethod() {
val subcomponent =
yourSubcomponentBuilder.daggerModule(DaggerModule(false)).build()
val anotherClass = subcomponent.anotherClass()
// ...
}
}
Constructor values in Hilt-managed components
The most difficult case would be where your Module would want separate values in each of your Hilt-managed components, e.g. each Activity needing to pass a different constructor argument. In that case you might need to rephrase the customBoolean (or other parameters) as deriving the value from the Activity instance itself. This maintains Hilt's expectation that it can create an Activity component for each Activity instance that Android unpredictably creates or recreates, and it can do so without specifying any other constructor parameters.
I have the following module that is used in the data layer of my application which is a plain Android Library.
#Module
interface MapperModule {
#Binds
fun bindDomainToDataMapper(domainToDataMapperImp: DomainToDataMapperImp)
: DomainToDataMapper<TodoTaskEntity, ToDoTaskModel>
#Binds
fun bindDataToDomainMapper(dataToDomainMapperImp: DataToDomainMapperImp)
: DataToDomainMapper<ToDoTaskModel, TodoTaskEntity>
}
I am just wondering what the #InstallIn scope should be as this is the Data Layer so is not specific to any android components.
I was thinking of using #InstallIn(SingleComponent::class) but I don't want these classes to be singleton.
Any ideas of what this should be?
Hilt has predefined components for Android that are managed for you. However, there may be situations where the standard Hilt components do not match the object lifetimes or needs of a particular feature
Custom component limitations
Custom component definitions currently have some limitations:
Components must be a direct or indirect child of the
SingletonComponent. Components may not be inserted between any of the
standard components. For example, a component cannot be added between
the ActivityComponent and the FragmentComponent.
To create a custom Hilt component, create a class annotated with #DefineComponent. This will be the class used in #InstallIn annotations.
The parent of your component should be defined in the value of the #DefineComponent annotation. Your #DefineComponent class can also be annotated with a scope annotation to allow scoping objects to this component.
#DefineComponent(parent = SingletonComponent::class)
interface MyCustomComponent
A builder interface must also be defined. If this builder is missing, the component will not be generated since there will be no way to construct the component. This interface will be injectable from the parent component and will be the interface for creating new instances of your component. As these are custom components, once instances are built, it will be your job to hold on to or release component instances at the appropriate time.
Builder interfaces are defined by marking an interface with #DefineComponent.Builder. Builders must have a method that returns the #DefineComponent type. They may also have additional methods (like #BindsInstance methods) that a normal Dagger component builder may have.
#DefineComponent.Builder
interface MyCustomComponentBuilder {
fun fooSeedData(#BindsInstance foo: Foo): MyCustomComponentBuilder
fun build(): MyCustomComponent
}
While the #DefineComponent.Builder class can be nested within the #DefineComponent, it is usually better as a separate class. It may be separated into a different class as long as it is a transitive dependency of the #HiltAndroidApp application or #HiltAndroidTest test. Since the #DefineComponent class is referenced in many places via #InstallIn, it may be better to separate the builder so that dependencies in the builder do not become transitive dependencies of every module installed in the component.
For the same reason of avoiding excessive dependencies, methods are not allowed on the #DefineComponent interface. Instead, Dagger objects should be accessed via entry points.
#EntryPoint
#InstallIn(MyCustomComponent::class)
interface MyCustomEntryPoint {
fun getBar(): Bar
}
class CustomComponentManager #Inject constructor(
componentBuilder: MyCustomComponentBuilder) {
fun doSomething(foo: Foo) {
val component = componentBuilder.fooSeedData(foo).build();
val bar = EntryPoints.get(component, MyCustomEntryPoint::class.java).getBar()
// Don't forget to hold on to the component instance if you need to!
}
Conclusion:
Even if you create a custom component indirectly, it will look like a Singleton.
Even if you use #InstallIn(SingleComponent::class) without #Singleton annotation these object won' t be singleton. They will be non-scoped objects, and for every request, you will have new instance for these classes.
I was thinking of using #InstallIn(SingleComponent::class) but I don't want these classes to be singleton.
It means you can use #InstallIn(SingleComponent::class) without #Singleton annotation.
This is a Canonical Question because this is a common error with Dagger 2.
If your question was flagged as a duplicate please read this post carefully and make sure to understand what this error means and why it occured. If this post does not work for you make sure to include where and how you provide the mentioned classes and include the full error message in your question like the one here.
I tried to use a dependency with Dagger 2, but I receive the following error when I try to compile my project:
error: com.example.MyDependency cannot be provided without an #Inject constructor or from an #Provides-annotated method.
com.example.MyDependency is provided at
com.example.MyComponent.myDependency()
What does this mean and how can I fix it?
I have a component and tried to provide a dependency. My basic setup looks like this:
// this is the dependency I try to use
class MyDependency {}
#Component
interface MyComponent {
// I want to make it accessible to be used with my component
MyDependency myDependency();
}
tl;dr You forgot to either add an #Inject to your constructor so that Dagger can use Constructor Injection to provide the object, or you need some method in one of your Modules that creates or binds the object.
What's going on?
Have a good look at the error message: It states that you try to request a dependency but Dagger has no way to provide or create it. It simply does not know how to, because it cannot be provided without an #Inject constructor or from an #Provides-annotated method.
A close look at the error message shows the class (a) that you are trying to provide and the component (b) that needs it.
com.example.MyDependency (a) is provided at
com.example.MyComponent.myDependency() (b)
You have to make sure that (b) can create or provide (a) to fix your issue.
It looks a bit more complex if you tried to inject your dependency somewhere else, but you can still see the full stack of events—in this case a constructor injection missing a dependency. The class (a) that you are trying to provide and the location (b) where Dagger tried injecting it. It also tells you where that dependent class was created (c) and again the component (d) that failed providing (a).
com.example.MyDependency cannot be provided without an #Inject constructor or from an #Provides-annotated method.
com.example.MyDependency (a) is injected at
com.example.DependentClass.(dependency) (b)
com.example.DependentClass is provided at (c)
com.example.MyComponent.myDependency() (d)
The same applies here: Make sure that (d) knows how to provide (a) and you're good to go.
How do I fix this?
Have a look at the error as shown above. Make sure you understand where it occured and what you are trying to inject. Then tell Dagger how to provide your object.
an #Inject constructor
As the error states, you try to use MyDependency but MyComponent does not know how to do that. If we have a look at the example it becomes clear why:
class MyDependency {}
The class has no #Inject annotated constructor! And there is no other module in the component, so there is nothing Dagger could do.
If you want to use constructor injection you can just add an #Inject annotated constructor and are done. Dagger will see this constructor and know how to create your class.
class MyDependency {
#Inject
MyDependency() { /**/ }
}
That is all you have to do when you can make use of constructor injection.
from an #Provides-annotated method
The error message states a second option, which allows you to provide an object if you don't want—or can't—use constructor injection. You can also add a #Provides annotated method to a module and add this module to your component.
#Module
class MyModule {
#Provides
MyDependency provideMyDependency() {
return new MyDependency();
}
}
#Component(modules = MyModule.class)
interface MyComponent {
MyDependency myDependency();
}
This way Dagger can use your module to create and provide your dependency. It is a little bit more boilerplate than using Constructor Injection, but you will have to use Modules for everything that needs further setup or that does not have an annotated constructor, e.g. third party libraries like Retrofit, OkHttp, or Gson.
There are also other ways to provide a dependency from a component. A #SubComponent has access to its parents dependencies, and a component dependency can expose some of its dependencies to its dependent components. But at some point everything Dagger provides needs to either have an #Inject constructor or a Module providing it.
But I did add MyDependency!
Pay close attention to the details. You probably are using an interface when you are only providing the implementation, or try to use a parent class when Dagger only knows about the subclass.
Maybe you added a custom #Qualifier or used #Named("typeA") with it. To Dagger this is a completely different object! Double check that you actually provide and request the same dependency.
Read the error and make sure that you either have an #Inject annotated constructor, a module that has a #Provides method that provides that type, or a parent component that does.
What if I want to provide an implementation for my interface?
A simple example like the following shows how one class extends another:
class MyDependency extends MyBaseDependency {
#Inject MyDependency() { super(); }
}
This will inform Dagger about MyDependency, but not about MyBaseDependency.
If you have one class implementing an interface or extending a super class you have to declare that. If you provide MyDependency this does not mean that Dagger can provide MyBaseDependency. You can use #Binds to tell Dagger about your implementation and provide it when the super class is required.
#Module
interface MyModule {
#Binds
MyBaseDependency provideMyBaseDependency(MyDependency implementation);
}
Say I have a class (or a #Provides method) annotated with #Singleton. This makes sense to me, whenever a dependency is provided from this class, the same instance will always be returned.
What I am trying to understand is why there is then a requirement for components that use that module to also be marked as #Singleton. The purpose of adding a scope to a component does not make sense to me. A component is an interface, that dagger uses to implement the actual injection.
If I try to compile my app with my dependency class marked as #Singleton, but do not have #Singleton marked on a component that injects this dependency, I get an error.
com.example.whatever.MyComponent (unscoped) cannot depend on scoped components
Adding #Singleton to the component makes this error go away, but I want to understand why. Can anyone help me understand this? Thanks!
Adding #Singleton on your component allows you to use #Singleton on your provider methods in your module you specify for your component. Scoped providers make it so that you can have only one instance from that given module without any additional magic beyond what Dagger2 generates for you.
#Singleton
#Component(module={BlahModule.class})
public interface SingletonComponent {
Blah blah();
}
#Module
public class BlahModule {
#Provides
#Singleton
public Blah blah() {
return new BlahImpl();
}
}
According to the Dagger 2 design doc, it is meant to make intention clear ("a declaration of intention") and to allow for better compile-time checking.
That declaration enables dagger to enforce the following constraints:
A given component may only have bindings (including scope annotations
on classes) that are unscoped or of the declared scope. I.e. a
component cannot represent two scopes. When no scope is listed,
bindings may only be unscoped.
A scoped component may only have one
scoped dependency. This is the mechanism that enforces that two
components don’t each declare their own scoped binding. E.g. Two
Singleton components that each have their own #Singleton Cache would
be broken.
The scope for a component must not appear in any of its
transitive dependencies. E.g.: SessionScoped -> RequestScoped ->
SessionScoped doesn’t make any sense and is a bug.
Singleton is
treated specially in that it cannot have any scoped dependencies.
Everyone expects Singleton to be the “root”.
This also makes some sense given the implementation of Dagger 2: Because Scopes are implemented via memoization and the user is responsible for instantiating a new Component instance for every new scope, then it makes sense that the Component has a lifetime (and set of provisions) to which the scope also applies.
What is the difference between the #Singleton annotation on Dagger2 #Component annotated classes, and #Provides annotated methods in modules?
If I have one module in which all methods are annotated with a #Singleton annotation, and a component with the same annotation which includes that module, what is the purpose of this?
#Singleton
#Component(...)
public interface AppComponent {
// ...
}
And
#Provides #Singleton Context provideContext() { return context; }
Annotating the #Provides method (or the class with an #Inject constructor) tells Dagger to implement the actual scoping functionality whereas annotating the component (which is necessary) doesn't have any functionality, but tells Dagger "I allow this component to contain bindings of this scope". Note that you can still have unscoped bindings in a scoped component, but not the other way around.
It's well within the use of a Java annotation to provide documentation to reader, which is what you're probably seeing in your first example. It's useful there so the reader can know the intended use of the class/interface without having to know the mechanism by which its instance is created or managed.