Introduction:
When developing Android applications using Dagger 2 for dependency injection in multi-module projects, you may encounter challenges that result in runtime errors. One common issue is the “lateinit property repository has not been initialized” error, which can be frustrating and hinder the smooth execution of your app. In this blog post, we will explore the root causes of this error and provide a comprehensive solution to help you overcome it.
Understanding Dagger 2 and Multi-Module Projects:
Dagger 2 is a powerful framework for managing dependencies in Android applications. In multi-module projects, the architecture is divided into a core module and several feature modules that depend on the core module. Dagger 2 allows you to define component interfaces in each module, establishing a dependency graph that handles object creation and injection.
The Error:
The “lateinit property repository has not been initialized” error typically occurs when you attempt to access a property marked as lateinit before it has been properly initialized by Dagger. In your code snippet, the MyViewModel class includes a repository property that should be injected using Dagger’s @Inject annotation. However, due to the timing of the injection, the property may not be initialized when accessed, resulting in the runtime error.
Utilizing ViewModelFactory and Dagger:
To resolve the “lateinit property repository has not been initialized” error, we need to modify our approach to ViewModel creation and leverage the power of Dagger. Let’s walk through the steps to implement a solution:
Step 1: Constructor Injection in ViewModel:
In your MyViewModel class, ensure that you use constructor injection to provide the repository dependency. This guarantees that the dependency is properly initialized when the ViewModel is created. Update your code as follows:
code
class MyViewModel @Inject constructor(private val repository: MyRepository): ViewModel() {
val data = repository.getData()
}
Step 2: Creating a ViewModelFactory:
To instruct the ViewModelProvider on how to instantiate your ViewModel, we need to create a custom ViewModelFactory. This factory class will be responsible for providing the necessary dependencies to the ViewModel constructor. Implement the following code:
code
class ViewModelFactory @Inject constructor(private val viewModels: MutableMap<Class<out ViewModel>, Provider<ViewModel>>) :
ViewModelProvider.Factory {
override fun <T : ViewModel?> create(modelClass: Class<T>): T =
viewModels[modelClass]
?.get() as T
}
Step 3: Configuring Dagger to Create ViewModelFactory:
Next, we need to configure Dagger to create our custom ViewModelFactory. This involves creating a generic ViewModelModule class and providing the necessary bindings. Implement the following code:
code
@Module
abstract class ViewModelModule {
@Binds
internal abstract fun bindsViewModelFactory(factory: ViewModelFactory): ViewModelProvider.Factory
@Binds
@IntoMap
@ViewModelKey(MyViewModel::class)
internal abstract fun bindsMyViewModel(viewModel: MyViewModel): ViewModel
}
Make sure to include the ViewModelModule in your Dagger component:
code
@Component(modules = [ViewModelModule::class]
)
@Singleton
interface AppComponent {
// Component methods...
}
Conclusion:
By following the above solution, you can overcome the “lateinit property repository has not been initialized” error in your multi-module Android project using Dagger 2. Implementing constructor injection in your ViewModel, creating a custom ViewModelFactory, and configuring Dagger to provide the ViewModel instances will ensure proper initialization and injection of dependencies. This will lead to a more stable and efficient Android application.
