kotlin-backstack

Backstack for Model-View-Presenter (MVP) Views in a Fragment-less design, written in Kotlin.

Why?

With an MVP architecture, you may want to do away with Android's Fragments, keep Activities to a minimum, and have clean Models, Views and Presenters. To manage your Views, some kind of backstack is required...

How do I use this library?

1. git clone this library to your machine

Put this somewhere easily-accessible.

2. Add the library to your project

This can be done in one of two ways:

As a library module

• a. In Android Studio, right-click your project in the 'Project' tab, and select Open Module Settings
• b. Click the + (circled) to add a module
• c. In the Create New Module window, under Import..., set the Source Directory to the inner backstack module within the saved library project (i.e. backstack/backstack)

.aar file

• a. Copy backstack/backstack/build/outputs/aar/backstack-release.aar
• b. Paste to <app-name>/<app-module>/libs/
• c. Ensure your app module's Gradle build script imports backstack-release.aar:

Gradle build configuration scripts are written in either Groovy DSL or Kotlin DSL (domain-specific language).

If Kotlin DSL (build.gradle.kts):

dependencies {
    implementation(files("libs/backstack-release.aar"))
}

If Groovy DSL (build.gradle):

dependencies {
    implementation files('libs/backstack-release.aar')
}

3. Setup your Activity

Ensure your Activity implements BackStack.ActivityInterface.

Below is a guide of an Activity implementation: you can view a working example in the backstackexample module of this project.

class MainActivity : AppCompatActivity(), BackStack.ActivityInterface {
    private lateinit var binding: ActivityMainBinding
    private val backstack = BackStack(this)
    
    /**
     * Notes:
     * - View Binding (https://developer.android.com/topic/libraries/view-binding) is in-use
     * - Content set, view binding, and Model object creation should be done before call 
     * to `backstack.onCreate()`.
     */
    override fun onCreate(savedInstanceState: Bundle?) {
        binding = ActivityMainBinding.inflate(layoutInflater)
        setContentView(binding.root)
        model = Model()
        backstack.onCreate()
        super.onCreate(savedInstanceState)
    }

    override fun onBackPressed() {
        super.onBackPressed()
        backstack.goBack()
    }

    override fun getInitialView(): BackStackView {
        return ExampleView()
    }

    override fun addView(view: ViewGroup) {
        binding.container.addView(view)
    }

    override fun removeAllViews() {
        binding.container.removeAllViews()
    }

    /**
     * I have opted to create the Model in onCreate().
     */
    override fun getModel(): ModelInterface {
        return model
    }

    override fun getContext(): Context {
        return this
    }
}

4. Setup your view(s)

Assumption: you already have an MVP architecture setup for this application - if not, see the code in backstackexample for an example:

class ExampleView: BackStackView() {
    private lateinit var presenter: ExamplePresenterInterface
    private lateinit var binding: ExampleViewBinding

    /********** public */
    
    override fun getLayout(): Int = R.layout.example_view

    override fun onCreate(backstack: BackStackInterface, model: ModelInterface,
                          context: AndroidContextInterface) {
        binding = ViewBinding.bind(view!!)
        setupButtonOnClickListener()
        /** This should be last as Presenter will likely use views defined above. **/
        this.presenter = ExamplePresenter(this, model as ExampleModelInterface, backstack)
    }

    override fun onResume(context: AndroidContextInterface) {
        binding = ViewBinding.bind(view!!)
        this.presenter.onResume()
    }
}

Notes:

• I have not tested any kind of compatibility with Jetpack Compose.