For AppComponent, we can use the @Singleton scope annotation that is the only scope annotation that comes with the javax.inject package. If we try to build again we get an error very similar to what we got before! Create a local variable before checking if the user is logged in or not. AppComponent) to our custom Application: MyApplication. Sometimes, you might want to provide the same instance of a dependency in a Component for multiple reasons: Use Scopes to have a unique instance of a type in a Component. Since RegistrationComponent is attached to the RegistrationActivity lifecycle, we have to keep a reference to the component in the Activity in the same way we kept the reference to the appComponent in the Application class. The code for that is in app/src/androidTest/java/com/example/android/dagger/MyCustomTestRunner.kt file. Now a RegistrationComponent will always provide the same instance of RegistrationViewModel. You can follow me on Medium, Twitter, Facebook, and Reddit for little tips and learning on mobile development, medium writing, etc related topics. Hey, you know what? Let's fix that by refactoring the Settings code to use Dagger. LoginComponent and RegistrationComponent are managed by its Activities but UserComponent can inject more than one Activity and the number of Activities could potentially increase. To delay the creation of the Fragment until requested by instantiate we utilize the Provider wrapper. Android Architecture Components ViewModel, Using Dagger in Android apps documentation. Now, we can subclass MyApplication and use TestAppComponent in MyTestApplication: Note: If you cannot import DaggerTestAppComponent, try to run the instrumentation tests as specified below and then try importing it. There are other annotations that can be useful in an Android project. So in short, just add lateinit var info: Info to replace the previously removed line. It generates code at compile-time using an annotation processor. Take a moment to familiarize yourself with the structure of the project.
If you try to build the app, MyTestApplication gives a compilation error as you have to remove the userManager instance from the class. RegistrationActivity is already using Dagger to manage its dependencies!
Create a new instance of RegistrationComponent in the onCreate method before calling super.onCreate and inject registrationComponent instead of injecting the activity to the appComponent: If you noticed, the variable registrationComponent is not annotated with @Inject because we're not expecting that variable to be provided by Dagger.
I want a little magic box that does the magic instantiating my member variable”, I declare my magic box like this (as an interface), I call it MagicBox just to make it different from other tutorials, so you know you could name it anything. Let’s get back to the actual code. There, create a new file called TestStorageModule.kt whose path is app/src/androidTest/java/com/example/android/dagger/di/TestStorageModule.kt. Fear not! Multibindings move the complexity from the Factory into Dagger modules which has introduces its own set of tradeoffs. The implementation is specified by adding a parameter with the interface implementation type (i.e.
Kotlin is the way of doing things today. Hey, don’t compile and run the above code, it will CRASH !
Note that Settings will cause the app to crash because it hasn't been refactored to use Dagger. We need to specify all the modules in this test Component too. Use @BindsInstance for objects that are constructed outside of the graph (e.g. A @Component interface gives the information Dagger needs to generate the graph at compile-time. But I think for a dummy like me, digesting this simple piece is a good start, and my brain needs to rest a bit to continue. Let's start refactoring the Registration flow to use Dagger. But we also want a new instance of RegistrationViewModel whenever there's a new registration flow. For field injection (that is commonly used in Activities and Fragments), we annotate with @Inject the fields that we want Dagger to provide. As UserManager has its constructor annotated with @Inject, Dagger will use it to create instances. When you run again, since we registered a user before, you'll be presented with the Login screen. You don't have to use Dagger-related code for unit tests. With Dagger 2 created, one could now make Info magically appears. Since the introduction of Jetpack, Google has recommended a Single Activity architecture which provides a convenient single entry point to application to create Fragments and the rest of the dependency graph. We're adding two types of Storage to the graph: RegistrationStorage and LoginStorage.
Dagger is one of the most popular frameworks for Dependency injection in Android Development. Multibindings are counterproductive to our goal of reducing complexity and thus won’t be covered. The test should run and pass. Therefore, we'll have the same instance provided anytime an object needs Context. If the UserManager needs to create new instances of UserComponent, it needs to access the UserComponent factory. Android doesn’t allow me to simply add any argument to its Activity’s constructor .
Note: This article is a 10 minute fun read. If you prefer a quicker and shorter tutorial, check out the 4 minute version of Even Simpler Dagger 2 Tutorial. Since the Fragment is annotated with @Inject constructor, Dagger does not require any additional configuration to be able to manage this class. Just trust Lord Dagger 2, and he shall provide. To add Dagger to your project, open the app/build.gradle file and add the two Dagger dependencies and the kapt plugin to the top of the file. The Main page should appear after the Registration flow! That’s it, we’re done. That's because kapt is not acting on the androidTest folder. It’s a way for me to tell Dagger 2, “Hey! UserManager has a dependency on Storage but since it's already in the graph, nothing else is needed.
This will be the topic for the last section of the codelab about work assignments. How to reuse instances of objects in different containers using Scopes. We need to tell Dagger what implementation of Storage we want to use. You understand Dependency Injection and know what the benefits of using Dagger in your Android app are. With the @Inject annotation, Dagger knows: For simplicity, RegistrationViewModel is not an Android Architecture Components ViewModel; it's just a regular class that acts as a ViewModel.
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