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Fragments

Tangle performs Fragment injection using constructor injection, just like the rest of a typical Dagger/Anvil graph. There are several steps to configuration, with two different paths at the end.

1. Set up Gradle​

// any Android module's build.gradle.kts
plugins {
  id("android-library") // or application, etc.
  kotlin("android")
  id("com.rickbusarow.tangle")
}

tangle {
  fragmentsEnabled = true // default is null
}

2. Use Anvil for the app-scoped Component​

Tangle uses the MergeComponent annotation from Anvil to identify the application's Component and add its own dependencies to the Dagger graph.

For anyone already using Anvil, there's probably nothing to be done here.

Anvil uses KClass<T> references to define scopes. A common pattern is to define an AppScope class specifically for this purpose in a low-level shared (Gradle) module:

package myApp.core.anvil

abstract class AppScope private constructor()

Then at your application Component, use MergeComponent with this scope:

package myApp.app

import com.squareup.anvil.annotations.MergeComponent
import myApp.core.anvil.AppScope

@MergeComponent(AppScope::class)
interface MyAppComponent

3. Set the custom FragmentFactory​

New Fragment instances are provided by TangleFragmentFactory. This custom factory is automatically added to any Dagger graph for any @MergeComponent-annotated Component.

note

If a requested Fragment is not contained within Tangle's bindings, TangleFragmentFactory will fall back to using the default initialization with an empty constructor. This means that large projects can be migrated gradually.

If a project was already doing Fragment constructor injection using vanilla Dagger, they were probably already binding into a Map<Class<out Fragment>, Provider<@JvmSuppressWildcards Fragment>>. That is what Tangle uses, so existing multi-bound graphs will often support gradual migrations as well.

Any FragmentManager used within the application will need to have its fragmentFactory property set to a TangleFragmentFactory instance. This means the AppCompatActivity.supportFragmentManager, and possibly Fragment.childFragmentManager as well. This is easiest if your application uses an abstract base class.

abstract class BaseActivity : AppCompatActivity() {

  override fun onCreate(savedInstanceState: Bundle?) {
    supportFragmentManager.fragmentFactory = Components.get<BaseActivityComponent>()
                                              .tangleFragmentFactory
    super.onCreate(savedInstanceState)
  }
}
Click to see how Components works

In a core module, define this singleton.

package myApp.core.anvil

object Components {
  @PublishedApi
  internal val _components = mutableSetOf<Any>()

  /** Set by Application class after creating app component */
  fun add(component: Any) {
    _components.add(component)
  }

  inline fun <reified T> get(): T = _components
    .filterIsInstance<T>()
    .single()
}

In your application, save off the AppComponent instance.

package myApp.core.anvil

class MyApplication : Application() {

  override fun onCreate() {
    val component = DaggerMyAppComponent.factory()
                      .create(/*...*/)

    Components.add(component)

    super.onCreate()
  }
}

Anywhere you need to, create a "component" interface with whatever dependency properties you need, and annotate it with @ContributesTo(<some scope definition>). Your AppComponent will automatically implement this interface, which means that an implementation of it will be stored in Components.

import com.squareup.anvil.annotations.ContributesTo

@ContributesTo(AppScope::class)
interface BaseActivityComponent {
  val tangleFragmentFactory: TangleFragmentFactory
}

Now, Components.get<BaseActivityComponent>() will return MyAppComponent safely cast to BaseActivityComponent, and you can access its properties.

val fragmentFactory = Components.get<BaseActivityComponent>()
                                .tangleFragmentFactory

4. Contribute Fragments to the graph​

Finally, add the Fragments themselves. For basic injection, the only difference from any other constructor-injected class is that you must add the ContributesFragment annotation. This will ensure that the Fragment is included in the TangleFragmentFactory.

import tangle.fragment.ContributesFragment

@ContributesFragment(AppScope::class)
class MyFragment @Inject constructor(
  val myRepository: MyRepository
) : Fragment() {
  // ...
}

5. Create Fragments with the FragmentManager​

All the pieces are now in place, and your FragmentManagers are able to create Fragments with Dagger dependencies.

class MyActivity: BaseActivity() {

  override fun onCreate(savedInstanceState: Bundle?) {
    super.onCreate(savedInstanceState)
    supportFragmentManager.beginTransaction()
      .add<MyFragment>(R.id.fragmentContainer)
      .commit()
  }
}

Next step -- "Assisted" Bundle injection​

Tangle is able to generate type-safe factories for Bundle arguments, similar to AssistedInject. Read about this more in bundle injection.

@ContributesFragment(AppScope::class)
class MyFragment @FragmentInject constructor() : Fragment() {

  val name by arg<String>("name")

  @FragmentInjectFactory
  interface Factory {
    fun create(@TangleParam("name") name: String): MyFragment
  }
}