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Dagger ‐ Scoping, normal example using singleton

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Devrath edited this page Oct 6, 2023 · 11 revisions

Observations

  • Scoping is a concept that helps to limit the instance lifecycle to a certain timeline.
  • After the timeline is complete the instance is not active and if needed it has to be re-instantiated.
  • The @component can be considered as a container and all the annotated with the container will be singleton to this container.
  • In this example you can see that we have created an annotation which is basically a singleton and we added it into the @module and @Component areas.
  • This ensures that until the component reference is destroyed, No matter how many times we use the instance of a class, it returns the same memory reference.
  • But when we retate the screen, The activity is destroyed and recreated so the component is recreated in example below so observe there is a new memory address.

Output

// ----> When the Screen is first loaded
connInterface1 reference---> 226246109
connInterface1 reference---> 226246109
// ----> App Screen is rotated and 
connInterface1 reference---> 8298091
connInterface1 reference---> 8298091

Code

implementations

Connection.kt

interface Connection {
    fun connect(endpoint:String)
}

HttpConnection.kt

class HttpConnection @Inject constructor() : Connection {
    override fun connect(endpoint: String) {
        PrintUtils.printLog("HttpConnection made")
    }
}

HttpsConnection.kt

class HttpsConnection @Inject constructor(): Connection {
    override fun connect(endpoint: String) {
        PrintUtils.printLog("HttpsConnection made")
    }
}

NetworkLibrary.kt

class NetworkLibrary @Inject constructor( val connection: Connection) {
    fun initilizeNetworkLibrary() {
        connection.connect("www.client.com")
        PrintUtils.printLog("Network library is initialized")
    }
}

Scopes

ApplicationScope.kt

@Scope
@MustBeDocumented
@Retention(AnnotationRetention.RUNTIME)
annotation class ApplicationScope

Modules

HttpConnectionModule.kt

@Module
@DisableInstallInCheck
class HttpConnectionModule {
    @Provides
    fun provideHttpConnection() : Connection { return HttpConnection() }
}

HttpConnectionModule.kt

@Module
@DisableInstallInCheck
class HttpsConnectionModule {
    @ApplicationScope
    @Provides
    fun provideHttpsConnection() : Connection { return HttpsConnection() }
}

Components

ConnectionComponent.kt

@ApplicationScope
@Component(modules = [HttpsConnectionModule::class])
interface ConnectionComponent {
    fun inject(activity: IntroScopeDemoActivity)
    fun provideHttpsConnection() : HttpsConnection
}

Activity

MyActivity.kt

class MyActivity : AppCompatActivity() {

    @Inject lateinit var connInterface1 : Connection
    @Inject lateinit var connInterface2 : Connection

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_intro_scope_demo)

        val comp = DaggerConnectionComponent.builder().build()
        comp.inject(this@IntroScopeDemoActivity)

        PrintUtils.printLog("connInterface1 reference---> "+connInterface1.hashCode().toString())
        PrintUtils.printLog("connInterface1 reference---> "+connInterface2.hashCode().toString())

    }
}
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