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The A,B and C

of

Lifecycle Components

Nishant Srivastava

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Nishant Srivastava

twitter.com/nisrulz

github.com/nisrulz

www.nisrulz.com

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Soundbrenner

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The Challenge

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The Challenge

Android activity lifecycle..

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The Challenge

Android activity lifecycle

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The Challenge

Android activity lifecycle

Many states

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The Challenge

Android activity lifecycle

Many states
Repeats on configuration changes

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The Challenge

Android activity lifecycle

Many states
Repeats on configuration changes

Not to forget...

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The Challenge

...the Fragment lifecycle.

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The Challenge

...the Fragment lifecycle.

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Architecture

Components

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Lifecycle

Components

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Lifecycle Components

Series of classes designed to help deal with lifecycles in a more consistent fashion.

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Lifecycle Components

Series of classes designed to help deal with lifecycles in a more consistent fashion.

Lifecycle
LifecycleOwner
LifecycleObserver

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Lifecycle

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Lifecycle

Series of states an object can be in.

For Android:�Object that defines Android lifecycle states. i.e. Activity & Fragment

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Lifecycle

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Lifecycle

dependencies {� def lifecycle_version = "1.1.1"� // Support library already depends on this (since v26.1.0)

// Both AppCompatActivity & Support Fragment implement

// LifecycleOwner interface.

// Lifecycles only

implementation "android.arch.lifecycle:runtime:$lifecycle_version"� ...�}

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Lifecycle

// Source code�public abstract class Lifecycle {� // Adds a LifecycleObserver� addObserver(@NonNull LifecycleObserver observer)�� // Removes the given observer from the observers list� removeObserver(@NonNull LifecycleObserver observer)�� // Current state of the Lifecycle� getCurrentState()�� // Compares the lifecycle states� isAtLeast(@NonNull State state)� ...�}

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Lifecycle

// Source code�public abstract class Lifecycle {� // Adds a LifecycleObserver� addObserver(@NonNull LifecycleObserver observer)�� // Removes the given observer from the observers list� removeObserver(@NonNull LifecycleObserver observer)�� // Current state of the Lifecycle� getCurrentState()�� // Compares the lifecycle states� isAtLeast(@NonNull State state)� ...�}

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Lifecycle

// Source code�public abstract class Lifecycle {� // Adds a LifecycleObserver� addObserver(@NonNull LifecycleObserver observer)�� // Removes the given observer from the observers list� removeObserver(@NonNull LifecycleObserver observer)�� // Current state of the Lifecycle� getCurrentState()�� // Compares the lifecycle states� isAtLeast(@NonNull State state)� ...�}

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LifecycleOwner

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LifecycleOwner

Interface that goes through Android Lifecycle.

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LifecycleOwner

Interface that goes through Android Lifecycle.

// Source code

public interface LifecycleOwner {� // Returns the Lifecycle of the provider.� @NonNull� Lifecycle getLifecycle();�}

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LifecycleOwner

class MainActivity : AppCompatActivity() {

// Missing myLifecycleObserver

� override fun onResume() {� // Add lifecycle observer� lifecycle.addObserver(myLifecycleObserver)� }�� override fun onStop() {� // Remove lifecycle observer� lifecycle.removeObserver(myLifecycleObserver)� }�}

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LifecycleOwner

Fun Fact:�Activities & fragments are not the only things with lifecycle by default

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LifecycleOwner

Fun Fact:�Activities & fragments are not the only things with lifecycle by default

You also have

LifecycleService
ProcessLifecycleOwner

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LifecycleService

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LifecycleService

A service that is also a LifecycleOwner

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LifecycleService

A service that is also a LifecycleOwner

// Source code

public class LifecycleService extends Service implements LifecycleOwner {� ...�}

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ProcessLifecycleOwner

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ProcessLifecycleOwner

Class that tracks the lifecycle of

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ProcessLifecycleOwner

Class that tracks the lifecycle of
whole application process

or

all the activities combined

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ProcessLifecycleOwner

Class that tracks the lifecycle of
whole application process

or

all the activities combined�

Useful for reacting to app coming to foreground or going to background

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ProcessLifecycleOwner

dependencies {� def lifecycle_version = "1.1.1"

� // For ProcessLifecycleOwner� implementation "android.arch.lifecycle:extensions:$lifecycle_version"� ...�}

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ProcessLifecycleOwner

ON_CREATE

ON_START & ON_RESUME

ON_PAUSE & ON_STOP

ON_DESTROY

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ProcessLifecycleOwner

ON_CREATE (Only 1 time)

ON_START & ON_RESUME

ON_PAUSE & ON_STOP

ON_DESTROY

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ProcessLifecycleOwner

ON_CREATE (Only 1 time)

ON_START & ON_RESUME (First Activity pass)

ON_PAUSE & ON_STOP

ON_DESTROY

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ProcessLifecycleOwner

ON_CREATE (Only 1 time)

ON_START & ON_RESUME (First Activity pass)

ON_PAUSE & ON_STOP (after 700ms delay)

ON_DESTROY

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ProcessLifecycleOwner

ON_CREATE (Only 1 time)

ON_START & ON_RESUME (First Activity pass)

ON_PAUSE & ON_STOP (after 700ms delay)

ON_DESTROY

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ProcessLifecycleOwner

ON_CREATE (Only 1 time)

ON_START & ON_RESUME (First Activity pass)

ON_PAUSE & ON_STOP (after 700ms delay)

ON_DESTROY

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ProcessLifecycleOwner

ON_PAUSE & ON_STOP (after 700ms delay)

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ProcessLifecycleOwner

ON_PAUSE & ON_STOP (after 700ms delay)

// Source code

public class ProcessLifecycleOwner implements LifecycleOwner {� static final long TIMEOUT_MS = 700; //mls� ...�}

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ProcessLifecycleOwner

Guarantee that ProcessLifecycleOwner won’t send any events if activities are

Destroyed
Recreated due to configuration change

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ProcessLifecycleOwner

Comes with cost:

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ProcessLifecycleOwner

Comes with cost:

extension artifact automatically adds <provider> element to your manifest

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ProcessLifecycleOwner

<manifest >� <application>� ...� <provider

android:name="android.arch.lifecycle.ProcessLifecycleOwnerInitializer"

android:authorities="com.example.app.lifecycle-trojan"� android:exported="false"� android:multiprocess="true" />

</application>

</manifest>

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ProcessLifecycleOwner

// Source code

// Internal class to initialize Lifecycles.�public class ProcessLifecycleOwnerInitializer extends ContentProvider {� @Override� public boolean onCreate() {� ...

ProcessLifecycleOwner.init(getContext());� return true;� }� ...�}

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ProcessLifecycleOwner

Side-effect:

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ProcessLifecycleOwner

Side-effect:

Inits ProcessLifecycleOwner even if your app does not use it!

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ProcessLifecycleOwner

Side-effect:

Inits ProcessLifecycleOwner even if your app does not use it!�

Why?

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ProcessLifecycleOwner

Side-effect:

Inits ProcessLifecycleOwner even if your app does not use it!�

Why? So that ProcessLifecycleOwner can be invoked as soon as process starts

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Application.ActivityLifecycleCallback

vs

ProcessLifecycleOwner

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Application.ActivityLifecycleCallback

vs or

ProcessLifecycleOwner

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Application.ActivityLifecycleCallback

// Source code

public interface ActivityLifecycleCallbacks {

� void onActivityCreated(Activity var1, Bundle var2);�� ...

� void onActivitySaveInstanceState(Activity var1, Bundle var2);�� void onActivityDestroyed(Activity var1);�}

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Application.ActivityLifecycleCallback

// Register for the callback

application� .registerActivityLifecycleCallbacks(object:� Application.ActivityLifecycleCallbacks{� override fun onActivityCreated(activity: Activity?, bundle: Bundle?) {}� ...� })

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ProcessLifecycleOwner

// Source code

public class ProcessLifecycleOwner implements LifecycleOwner {� ...� void attach(Context context) {� ...� Application app = (Application) context.getApplicationContext();� app.registerActivityLifecycleCallbacks� (new EmptyActivityLifecycleCallbacks() {� @Override� public void onActivityCreated(Activity activity,� Bundle savedInstanceState) { .. }� ...� });� }�}

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ProcessLifecycleOwner

// Source code

public class ProcessLifecycleOwner implements LifecycleOwner {� ...� void attach(Context context) {� ...� Application app = (Application) context.getApplicationContext();� app.registerActivityLifecycleCallbacks� (new EmptyActivityLifecycleCallbacks() {� @Override� public void onActivityCreated(Activity activity,� Bundle savedInstanceState) { .. }� ...� });� }�}

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ProcessLifecycleOwner

// Source code

public class ProcessLifecycleOwner implements LifecycleOwner {� ...� void attach(Context context) {� ...� Application app = (Application) context.getApplicationContext();� app.registerActivityLifecycleCallbacks� (new EmptyActivityLifecycleCallbacks() {� @Override� public void onActivityCreated(Activity activity,� Bundle savedInstanceState) { .. }� ...� });� }�}

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ProcessLifecycleOwner

// Source code

class EmptyActivityLifecycleCallbacks� implements Application.ActivityLifecycleCallbacks {�� @Override� public void onActivityCreated(Activity activity,� Bundle savedInstanceState) {

//Empty method body� }�� ...�}

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ProcessLifecycleOwner

// Source code

class EmptyActivityLifecycleCallbacks� implements Application.ActivityLifecycleCallbacks {�� @Override� public void onActivityCreated(Activity activity,� Bundle savedInstanceState) {

//Empty method body� }�� ...�}

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LifecycleRegistry

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LifecycleRegistry

Implementation of Lifecycle that can handle multiple observers

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LifecycleRegistry

Implementation of Lifecycle that can handle multiple observers

// Source code

public class LifecycleRegistry extends Lifecycle {� ...�}

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LifecycleRegistry

Implementation of Lifecycle that can handle multiple observers

// Source code

public class LifecycleRegistry extends Lifecycle {� ...�}

However, you need to dispatch the events yourself.

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LifecycleRegistry

class MyLifecycleOwner : LifecycleOwner {� private var registry: LifecycleRegistry = LifecycleRegistry(this)�� init {� registry.handleLifecycleEvent(Lifecycle.Event.ON_CREATE)� }�� override fun getLifecycle(): Lifecycle = registry�� fun startListening() {� registry.handleLifecycleEvent(Lifecycle.Event.ON_START)� }�� fun stopListening() {� registry.handleLifecycleEvent(Lifecycle.Event.ON_STOP)� }�}

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LifecycleRegistry

class MyLifecycleOwner : LifecycleOwner {� private var registry: LifecycleRegistry = LifecycleRegistry(this)�� init {� registry.handleLifecycleEvent(Lifecycle.Event.ON_CREATE)� }�� override fun getLifecycle(): Lifecycle = registry�� fun startListening() {� registry.handleLifecycleEvent(Lifecycle.Event.ON_START)� }�� fun stopListening() {� registry.handleLifecycleEvent(Lifecycle.Event.ON_STOP)� }�}

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LifecycleRegistry

class MyLifecycleOwner : LifecycleOwner {� private var registry: LifecycleRegistry = LifecycleRegistry(this)�� init {� registry.handleLifecycleEvent(Lifecycle.Event.ON_CREATE)� }�� override fun getLifecycle(): Lifecycle = registry�� fun startListening() {� registry.handleLifecycleEvent(Lifecycle.Event.ON_START)� }�� fun stopListening() {� registry.handleLifecycleEvent(Lifecycle.Event.ON_STOP)� }�}

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LifecycleRegistry

class MyLifecycleOwner : LifecycleOwner {� private var registry: LifecycleRegistry = LifecycleRegistry(this)�� init {� registry.handleLifecycleEvent(Lifecycle.Event.ON_CREATE)� }�� override fun getLifecycle(): Lifecycle = registry�� fun startListening() {� registry.handleLifecycleEvent(Lifecycle.Event.ON_START)� }�� fun stopListening() {� registry.handleLifecycleEvent(Lifecycle.Event.ON_STOP)� }�}

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LifecycleRegistry

class MyLifecycleOwner : LifecycleOwner {� private var registry: LifecycleRegistry = LifecycleRegistry(this)�� init {� registry.handleLifecycleEvent(Lifecycle.Event.ON_CREATE)� }�� override fun getLifecycle(): Lifecycle = registry�� fun startListening() {� registry.handleLifecycleEvent(Lifecycle.Event.ON_START)� }�� fun stopListening() {� registry.handleLifecycleEvent(Lifecycle.Event.ON_STOP)� }�}

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LifecycleRegistry

val myLifecycleOwner = MyLifecycleOwner()��// Missing myLifecycleObserver��// Add lifecycle observer�myLifecycleOwner.lifecycle.addObserver(myLifecycleObserver)

// Remove lifecycle observer�myLifecycleOwner.lifecycle.removeObserver(myLifecycleObserver)

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LifecycleObserver

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LifecycleObserver

An interface for observing a Lifecycle

// Source code�public interface LifecycleObserver {

// Empty

}

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LifecycleObserver

Two ways to implement

Annotation
Callback Interface

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LifecycleObserver

dependencies {� def lifecycle_version = "1.1.1"

� // For Annotation Support

annotationProcessor "android.arch.lifecycle:compiler:$lifecycle_version"� ...�}

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LifecycleObserver

class MyLifecycleObserver : LifecycleObserver {�� @OnLifecycleEvent(Lifecycle.Event.ON_CREATE)� fun init() {}�� @OnLifecycleEvent(Lifecycle.Event.ON_START)� fun onStart() {}� ...�� @OnLifecycleEvent(Lifecycle.Event.ON_DESTROY)� fun cleanup() {}�}

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LifecycleObserver

val myLifecycleOwner = MyLifecycleOwner()��// Add lifecycle observer�myLifecycleOwner.lifecycle.addObserver(myLifecycleObserver)

// Remove lifecycle observer�myLifecycleOwner.lifecycle.removeObserver(myLifecycleObserver)

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LifecycleObserver

val myLifecycleOwner = MyLifecycleOwner()��val myLifecycleObserver = MyLifecycleObserver()��// Add lifecycle observer�myLifecycleOwner.lifecycle.addObserver(myLifecycleObserver)

// Remove lifecycle observer�myLifecycleOwner.lifecycle.removeObserver(myLifecycleObserver)

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LifecycleObserver

val myLifecycleOwner = MyLifecycleOwner()��val myLifecycleObserver = MyLifecycleObserver()��// Add lifecycle observer�myLifecycleOwner.lifecycle.addObserver(myLifecycleObserver)

// Remove lifecycle observer�myLifecycleOwner.lifecycle.removeObserver(myLifecycleObserver)

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DefaultLifecycleObserver

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DefaultLifecycleObserver

Callback interface for listening to LifecycleOwner state changes.

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DefaultLifecycleObserver

Callback interface for listening to LifecycleOwner state changes.

Recommended over annotations if using Java 8 language.

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DefaultLifecycleObserver

android {� compileOptions {� sourceCompatibility JavaVersion.VERSION_1_8� targetCompatibility JavaVersion.VERSION_1_8� }�}��dependencies {� def lifecycle_version = "1.1.1"� // For DefaultLifecycleObserver� implementation "android.arch.lifecycle:common-java8:$lifecycle_version"� ...�}

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DefaultLifecycleObserver

// Source code

public interface DefaultLifecycleObserver extends FullLifecycleObserver {

� @Override� default void onCreate(@NonNull LifecycleOwner owner) { ... }�� ...�� @Override� default void onDestroy(@NonNull LifecycleOwner owner) { ... }�}

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DefaultLifecycleObserver

// Source code

interface FullLifecycleObserver extends LifecycleObserver {

� void onCreate(LifecycleOwner owner);

� void onStart(LifecycleOwner owner);�

...

� void onDestroy(LifecycleOwner owner);�}

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DefaultLifecycleObserver

class MyLifecycleObserver : DefaultLifecycleObserver {�� override fun onCreate(owner: LifecycleOwner) {}� ...� override fun onDestroy(owner: LifecycleOwner) {}�}

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LiveData

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LiveData

A lifecycle aware base class for encapsulating loading data

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LiveData

A lifecycle aware base class for encapsulating loading data

Lightweight implementation of Observer pattern

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LiveData

dependencies {� def lifecycle_version = "1.1.1"� // For LiveData� implementation "android.arch.lifecycle:livedata:$lifecycle_version"� ...�}

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LiveData

// Source Code�public abstract class LiveData<T> {� ...� protected void postValue(T value) {...} � ...� @MainThread� protected void setValue(T value) {...} � ...� protected void onActive() {...} � protected void onInactive() {...} �}

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LiveData

// Source Code�public abstract class LiveData<T> {� ...� protected void postValue(T value) {...} // Sets the value async� ...� @MainThread� protected void setValue(T value) {...} � ...� protected void onActive() {...} � protected void onInactive() {...} �}

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LiveData

// Source Code�public abstract class LiveData<T> {� ...� protected void postValue(T value) {...} // Sets the value async� ...� @MainThread� protected void setValue(T value) {...} // Sets the value sync� ...� protected void onActive() {...} � protected void onInactive() {...} �}

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LiveData

// Source Code�public abstract class LiveData<T> {� ...� protected void postValue(T value) {...} // Sets the value async� ...� @MainThread� protected void setValue(T value) {...} // Sets the value sync� ...� protected void onActive() {...} // Has active observers i.e in Start/Resume state� protected void onInactive() {...} �}

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LiveData

// Source Code�public abstract class LiveData<T> {� ...� protected void postValue(T value) {...} // Sets the value async� ...� @MainThread� protected void setValue(T value) {...} // Sets the value sync� ...� protected void onActive() {...} // Has active observers i.e in Start/Resume state� protected void onInactive() {...} // Has 0 active observers�}

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LiveData

class MySensorLiveData(context: Context?) : LiveData<Float>() {� val sensorManager: SensorManager? = context?

.getSystemService(Service.SENSOR_SERVICE) as SensorManager�

val sensorListener: SensorEventListener = object : SensorEventListener {� override fun onSensorChanged(event: SensorEvent?) {� // Set Value

setValue(event?.values?.get(0))� }� ...� }

}

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LiveData

class MySensorLiveData(context: Context?) : LiveData<Float>() {� val sensorManager: SensorManager? = context?

.getSystemService(Service.SENSOR_SERVICE) as SensorManager�

val sensorListener: SensorEventListener = object : SensorEventListener {� override fun onSensorChanged(event: SensorEvent?) {� // Set Value

setValue(event?.values?.get(0))� }� ...� }

}

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LiveData

class MySensorLiveData(context: Context?) : LiveData<Float>() {� ...� override fun onActive() {� ...� sensorManager?.registerListener(sensorListener,� sensorManager.getDefaultSensor(Sensor.TYPE_ACCELEROMETER),� SensorManager.SENSOR_DELAY_FASTEST)� }�� override fun onInactive() {� ...� sensorManager.unregisterListener(sensorListener)� }�}

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LiveData

class MySensorLiveData(context: Context?) : LiveData<Float>() {� ...� override fun onActive() {� ...� sensorManager?.registerListener(sensorListener,� sensorManager.getDefaultSensor(Sensor.TYPE_ACCELEROMETER),� SensorManager.SENSOR_DELAY_FASTEST)� }�� override fun onInactive() {� ...� sensorManager.unregisterListener(sensorListener)� }�}

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LiveData

val mySensorLiveData = MySensorLiveData(this)

�// Observe for values�mySensorLiveData.observe(this, Observer<Float>{ floatVal ->� // Update the UI�})

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ViewModel

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ViewModel

Hold & manage UI related data in Lifecycle conscious way

Survives configuration changes

Prevents unnecessary reloading of data

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ViewModel

dependencies {� def lifecycle_version = "1.1.1"� // For ViewModel� implementation "android.arch.lifecycle:viewmodel:$lifecycle_version"� ...�}

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ViewModel

// Source code�public abstract class ViewModel {

// Called when ViewModel is destroyed� protected void onCleared() {� }�}

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ViewModel