Power navigation	Multibackstack	Result listeners

Cicerone (a guide who gives information about antiquities and places of interest to sightseers) is a lightweight library that makes the navigation in an Android app easy.
It was designed to be used with the MVP/MVVM/MVI patterns but will work great with any architecture.

• Is not tied to Fragments
• Not a framework (very lightweight)
• Short navigation calls (no builders)
• Static typed checks for screen parameters!
• Lifecycle-safe!
• Functionality is simple to extend
• Suitable for Unit Testing

• Opening several screens inside single call (for example: deeplink)
• Provides FragmentFactory if it needed
• add or replace strategy for opening next screen (see router.navigateTo last parameter)
• Implementation of parallel navigation (Instagram like)
• Predefined navigator ready for Single-Activity apps
• Predefined navigator ready for setup transition animation

Add the dependency in your build.gradle:

dependencies {
    //Cicerone
    implementation("com.github.terrakok:cicerone:X.X.X")
}

Initialize the library (for example in your Application class):

class App : Application() {
    private val cicerone = Cicerone.create()
    val router get() = cicerone.router
    val navigatorHolder get() = cicerone.getNavigatorHolder()

    override fun onCreate() {
        super.onCreate()
        INSTANCE = this
    }

    companion object {
        internal lateinit var INSTANCE: App
            private set
    }
}

The Presenter calls the navigation method of Router.

class SamplePresenter(
    private val router: Router
) : Presenter<SampleView>() {

    fun onOpenNewScreen() {
        router.navigateTo(SomeScreen())
    }

    fun onBackPressed() {
        router.exit()
    }
}

Router converts the navigation call to the set of commands and sends them to CommandBuffer.

CommandBuffer checks whether there are the _"active"_ Navigator:

• If yes, it passes the commands to the Navigator. Navigator will process them to achive the desired transition.
• If no, then CommandBuffer saves the commands in a queue, and will apply them as soon as a new _"active"_ Navigator will appear.

fun executeCommands(commands: Array<out Command>) {
    navigator?.applyCommands(commands) ?: pendingCommands.add(commands)
}

Navigator processes the navigation commands. Usually it is an anonymous class inside Activity. Activity provides Navigator to the CommandBuffer in _onResume_ and removes it in _onPause_.

Attention: Use _onResumeFragments()_ with FragmentActivity (more info)

private val navigator = AppNavigator(this, R.id.container)

override fun onResumeFragments() {
    super.onResumeFragments()
    navigatorHolder.setNavigator(navigator)
}

override fun onPause() {
    navigatorHolder.removeNavigator()
    super.onPause()
}

These commands will fulfill the needs of the most applications. But if you need something special - just add it!

• Forward - Opens new screen
• Back - Rolls back the last transition
• BackTo - Rolls back to the needed screen in the screens chain
• Replace - Replaces the current screen

The library provides predefined navigator for Fragments and Activity. To use, just provide it with the container and FragmentManager.

private val navigator = AppNavigator(this, R.id.container)

A custom navigator can be useful sometimes:

private val navigator = object : AppNavigator(this, R.id.container) {
    override fun setupFragmentTransaction(
        screen: FragmentScreen,
        fragmentTransaction: FragmentTransaction,
        currentFragment: Fragment?,
        nextFragment: Fragment
    ) {
        //setup your animation
    }

    override fun applyCommands(commands: Array<out Command>) {
        hideKeyboard()
        super.applyCommands(commands)
    }
}

Describe your screens as you like e.g. create a Kotlin object with all application screens:

object Screens {
    fun Main() = FragmentScreen { MainFragment() }
    fun AddressSearch() = FragmentScreen { AddressSearchFragment() }
    fun Profile(userId: Long) = FragmentScreen("Profile_$userId") { ProfileFragment(userId) }
    fun Browser(url: String) = ActivityScreen { Intent(Intent.ACTION_VIEW, Uri.parse(url))  }
}

Additional you can use FragmentFactory for creating your screens:

fun SomeScreen() = FragmentScreen { factory: FragmentFactory -> ... }

//you have to specify screen parameters via new FragmentScreen creation
fun SelectPhoto(resultKey: String) = FragmentScreen {
    SelectPhotoFragment.getNewInstance(resultKey)
}

//listen result
fun onSelectPhotoClicked() {
    router.setResultListener(RESULT_KEY) { data ->
        view.showPhoto(data as Bitmap)
    }
    router.navigateTo(SelectPhoto(RESULT_KEY))
}

//send result
fun onPhotoClick(photo: Bitmap) {
    router.sendResult(resultKey, photoRes)
    router.exit()
}

To see how to add, initialize and use the library and predefined navigators see the sample project
(thank you @Javernaut for support new library version and migrate sample project to Kotlin!)

For more complex use case check out the GitFox (Android GitLab client)

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• Idea and code - Konstantin Tskhovrebov (@terrakok)
• Architecture advice, documentation and publication - Vasili Chyrvon (@Jeevuz)

MIT License

Copyright (c) 2017 Konstantin Tskhovrebov (@terrakok)
                   and Vasili Chyrvon (@Jeevuz)

Permission is hereby granted, free of charge, to any person obtaining a copy
of this software and associated documentation files (the "Software"), to deal
in the Software without restriction, including without limitation the rights
to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
copies of the Software, and to permit persons to whom the Software is
furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all
copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
SOFTWARE.