Android App Architecture & Navigation

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Android App Architecture & Navigation Bryan Herbst (@bryancherbst)

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Activities & Fragments

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STOP

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STOP If you like what you have, keep it

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When to use what?

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Where we’ve been

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In the beginning there was Activity

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Activity Entry point to your application

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Activity Entry point to your application Has a Window

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Activity Entry point to your application Has a Window Has a lifecycle

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Activity Entry point to your application Has a Window Has a lifecycle Responds to configuration changes

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Activity Entry point to your application Has a Window Has a lifecycle Responds to configuration changes ActivityManager handles back stack

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Activity Layout inflation View manipulation Click handlers Animations Navigation Menu creation Menu item callbacks Database calls Networking calls Disk I/O Sensor input Geolocation

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Activity Window transitions can be difficult !

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Activity Window transitions can be difficult A lot of plumbing !

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Activity Window transitions can be difficult A lot of plumbing Nuanced (and limited) backstack !

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Enter Honeycomb (3.0)

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No content

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Fragments!

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Fragment Has lifecycle (less than Activity)

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Fragment Has lifecycle (less than Activity) Backstack via FragmentManager

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Fragment Has lifecycle (less than Activity) Backstack via FragmentManager Composable

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Fragment Has lifecycle (less than Activity) Backstack via FragmentManager Composable Belong to an Activity

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Fragments Transactions are annoying !

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Fragments Transactions are annoying Lifecycles are annoying !

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Fragments Transactions are annoying Lifecycles are annoying Can still be too big !

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Fragments Transactions are annoying Lifecycles are annoying Can still be too big Bugs !

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Fragments Transactions are annoying Lifecycles are annoying Can still be too big Bugs Differences from Activity !

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Meanwhile

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View-based architecture

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View Draws things Reacts to user interaction

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View Almost no lifecycle No backstack !

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Where are we now?

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Single activity app Easier to manage transitions

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Single activity app Easier to manage transitions Composable UI elements

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Single activity app Easier to manage transitions Composable UI elements Google can be opinionated

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Don’t like lifecyles? Use Lifecycle

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class MainActivity : Activity { override fun onStart() { super.onStart() analytics.reportStart() } }

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activity.lifecycle .addObserver(AnalyticsObserver()) class AnalyticsObserver : LifecycleObserver { @OnLifecycleEvent(ON_START) fun trackPageLoad() { analytics.reportStart() } }

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activity.lifecycle .addObserver(AnalyticsObserver()) class AnalyticsObserver : LifecycleObserver { @OnLifecycleEvent(ON_START) fun trackPageLoad() { analytics.reportStart() } }

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Fragment refresher

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Which Fragments? Framework fragments Support fragments

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Which Fragments? Framework fragments Support fragments ! "

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Fragment transactions

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Fragment transactions fragmentManager.beginTransaction()

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Fragment transactions fragmentManager.beginTransaction() .add()

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Fragment transactions fragmentManager.beginTransaction() .remove()

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Fragment transactions fragmentManager.beginTransaction() .replace()

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Fragment transactions fragmentManager.beginTransaction() .show()

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Fragment transactions fragmentManager.beginTransaction() .hide()

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Fragment transactions fragmentManager.beginTransaction() .addToBackstack()

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Fragment transactions fragmentManager.beginTransaction() .commit()

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Fragment transactions fragmentManager.beginTransaction() .add() .replace() .hide() .addToBackstack() .commit()

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Transactions are asynchronous

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The IllegalStateException com.awesomeapp E/MainActivity: java.lang.IllegalStateException: Cannot perform this action after onSaveInstanceState

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The IllegalStateException FM State

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The IllegalStateException FM State add()

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The IllegalStateException FM State add()

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The IllegalStateException FM State add() hide()

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The IllegalStateException FM State add() hide() onStop()!!

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The IllegalStateException FM State add() hide() onStop()!! Persisted add() hide()

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The IllegalStateException FM State onStart() Persisted add() hide()

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The IllegalStateException FM State add() hide() Persisted add() hide() replace()

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The IllegalStateException After onSaveInstanceState any future changes may be lost

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Okay, but async transactions suck

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Commit() commit() executePendingTransactions() commitAllowingStateLoss() commitNow() commitNowAllowingStateLoss()

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Commit() commit() executePendingTransactions() commitAllowingStateLoss() commitNow() commitNowAllowingStateLoss()

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Commit() commit() executePendingTransactions() commitAllowingStateLoss() commitNow() commitNowAllowingStateLoss()

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Commit() commit() executePendingTransactions() commitAllowingStateLoss() commitNow() commitNowAllowingStateLoss()

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Back stack addToBackStack(null)

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Back stack popBackStack()

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Back stack addToBackStack("screenA")

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Back stack addToBackStack("screenA")

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Back stack addToBackStack("screenB")

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Back stack addToBackStack("screenC")

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Back stack popBackStack("screenA", 0)

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But that’s a lot of work

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Navigation

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Navigation Challenges Transitions

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Navigation Challenges Transitions Back stack management

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Navigation Challenges Transitions Back stack management Up vs. back

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Navigation Challenges Transitions Back stack management Up vs. back Passing data

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Navigation Challenges Transitions Back stack management Up vs. back Passing data Deep linking

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Android Jetpack: Navigation

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Principles Navigation is a stack

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Principles Navigation is a stack Up never exits the app

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Principles Navigation is a stack Up never exits the app Up = Back within your app

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Principles Navigation is a stack Up never exits the app Up = Back within your app Deep linking should yield the same stack

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Navigation (the library)

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Navigation library No more Fragment transactions!

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Navigation library No more Fragment transactions! No more startActivity()!

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Navigation library No more Fragment transactions! No more startActivity()! Just call navigate()

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Navigation Graph All the destinations in your app, plus the action that connect them.

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Navigation Graph New XML resource type!

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Navigation tooling

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Navigator What destination types are available?

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NavHost Where do those destinations reside?

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NavController How do I get there?

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Current Navigators ActivityNavigator

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Current Navigators ActivityNavigator FragmentNavigator

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Do the navigation Navigation .findNavController(view) .navigate(R.id.action_id)

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Destinations: Deep link Destinations can have deep links

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Actions: Animations Actions can have transition animations

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Actions: back stack Each action can define its own behavior

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Arguments Actions can all have arguments

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Arguments Works with deep links!

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Safeargs androidx.navigation.safeargs

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Safeargs androidx.navigation.safeargs Generates argument wrapper classes

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Safeargs Demo time!

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Demo time!

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Custom destination You can make your own Navigator!

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What’s missing Some integration with common elements like bottom navigation

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What’s missing Some integration with common elements like bottom navigation Shared element transitions

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What’s missing Some integration with common elements like bottom navigation Shared element transitions Nested navigation graphs

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What’s missing Some integration with common elements like bottom navigation Shared element transitions Nested navigation graphs Result data (e.g. startActivityForResult())

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What if I want to migrate to Navigation?

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I currently have…

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Single Activity

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Single Activity Set up navigation graph

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Single Activity Set up navigation graph Each Fragment is a destination

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Single Activity Set up navigation graph Each Fragment is a destination Every transaction is an action

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Single Activity Set up navigation graph Each Fragment is a destination Every transaction is an action Define arguments

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Single Activity Set up navigation graph Each Fragment is a destination Every transaction is an action Define arguments Replace transactions with NavController.navigate()

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Multiple activities Start by making a graph for each Activity

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Multiple activities Start by making a graph for each Activity If you want a single Activity, combine Activities one screen at a time

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Activity Chrome

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Activity Chrome CoordinatorLayout .setStatusBarBackgroundColor()

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Activity Features

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Activity Features activity.window .setSoftInputMode(SOFT_INPUT_ADJUST_PAN)

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More complex Watch for updates! Provide feedback!

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Resources https://developer.android.com /topic /libraries /architecture /navigation