The A, B and C of Lifecycle Components

[Droidcon Berlin '18] If you've been developing Android applications for a while now, you know the pain of handling the lifecycle just right. It’s a pain-point that has existed since the advent of Android, up until recently when Google released Architecture components. As an Android developer you are bugged by handling activity/fragment lifecycle and flow of data in tandem to the lifecycle changes day in and out. Making your code aware about the lifecycle of the process/activity/fragment makes you more confident as a developer and enables faster development. This session would enable you to understand Lifecycle components (ProcessLifecycleOwner, LifecycleOwner, LifecycleObserver) and how they are leveraged in other architecture components like LiveData and ViewModel.

Google Slides Link: https://docs.google.com/presentation/d/1b8mEH9hwwBxUiUk4xxib15sL7UIAYrP2TiSDXY9ZGS4

Transcript

1. Nishant Srivastava
   The A,B and C
   of
   Lifecycle Components
   

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2. Nishant Srivastava
   twitter.com/nisrulz
   github.com/nisrulz
   www.nisrulz.com
   

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3. Soundbrenner
   

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4. The Challenge
   @nisrulz #DCBERLIN18
   

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5. The Challenge
   Android activity lifecycle..
   @nisrulz #DCBERLIN18
   

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6. The Challenge
   Android activity lifecycle
   @nisrulz #DCBERLIN18
   

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7. The Challenge
   Android activity lifecycle
   - Many states
   @nisrulz #DCBERLIN18
   

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8. The Challenge
   Android activity lifecycle
   - Many states
   - Repeats on configuration
   changes
   @nisrulz #DCBERLIN18
   

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9. The Challenge
   Android activity lifecycle
   - Many states
   - Repeats on configuration
   changes
   Not to forget...
   @nisrulz #DCBERLIN18
   

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10. The Challenge
    ...the Fragment lifecycle.
    @nisrulz #DCBERLIN18
    

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11. The Challenge
    ...the Fragment lifecycle.
    @nisrulz #DCBERLIN18
    

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12. Architecture
    Components
    @nisrulz #DCBERLIN18
    

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13. Lifecycle
    Components
    @nisrulz #DCBERLIN18
    

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14. Lifecycle Components
    Series of classes designed to help deal with
    lifecycles in a more consistent fashion.
    @nisrulz #DCBERLIN18
    

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15. Lifecycle Components
    Series of classes designed to help deal with
    lifecycles in a more consistent fashion.
    - Lifecycle
    - LifecycleOwner
    - LifecycleObserver
    @nisrulz #DCBERLIN18
    

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16. Lifecycle
    @nisrulz #DCBERLIN18
    

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17. Lifecycle
    Series of states an object can be in.
    For Android:
    Object that defines Android lifecycle states.
    i.e. Activity & Fragment
    @nisrulz #DCBERLIN18
    

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18. Lifecycle
    @nisrulz #DCBERLIN18
    

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19. 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"
    ...
    }
    @nisrulz #DCBERLIN18
    

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20. 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)
    ...
    }
    @nisrulz #DCBERLIN18
    

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21. 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)
    ...
    }
    @nisrulz #DCBERLIN18
    

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22. 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)
    ...
    }
    @nisrulz #DCBERLIN18
    

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23. LifecycleOwner
    @nisrulz #DCBERLIN18
    

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24. LifecycleOwner
    Interface that goes through Android Lifecycle.
    @nisrulz #DCBERLIN18
    

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25. LifecycleOwner
    Interface that goes through Android Lifecycle.
    // Source code
    public interface LifecycleOwner {
    // Returns the Lifecycle of the provider.
    @NonNull
    Lifecycle getLifecycle();
    }
    @nisrulz #DCBERLIN18
    

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26. LifecycleOwner
    class MainActivity : AppCompatActivity() {
    // Missing myLifecycleObserver
    override fun onResume() {
    // Add lifecycle observer
    lifecycle.addObserver(myLifecycleObserver)
    }
    override fun onStop() {
    // Remove lifecycle observer
    lifecycle.removeObserver(myLifecycleObserver)
    }
    }
    @nisrulz #DCBERLIN18
    

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27. LifecycleOwner
    Fun Fact:
    Activities & fragments are not the only things
    with lifecycle by default
    @nisrulz #DCBERLIN18
    

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28. LifecycleOwner
    Fun Fact:
    Activities & fragments are not the only things
    with lifecycle by default
    You also have
    - LifecycleService
    - ProcessLifecycleOwner
    @nisrulz #DCBERLIN18
    

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29. LifecycleService
    @nisrulz #DCBERLIN18
    

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30. LifecycleService
    A service that is also a LifecycleOwner
    @nisrulz #DCBERLIN18
    

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31. LifecycleService
    A service that is also a LifecycleOwner
    // Source code
    public class LifecycleService extends Service implements LifecycleOwner {
    ...
    }
    @nisrulz #DCBERLIN18
    

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32. ProcessLifecycleOwner
    @nisrulz #DCBERLIN18
    

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33. ProcessLifecycleOwner
    - Class that tracks the lifecycle of
    @nisrulz #DCBERLIN18
    

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34. ProcessLifecycleOwner
    - Class that tracks the lifecycle of
    - whole application process
    or
    - all the activities combined
    @nisrulz #DCBERLIN18
    

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35. 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
    @nisrulz #DCBERLIN18
    

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36. ProcessLifecycleOwner
    dependencies {
    def lifecycle_version = "1.1.1"
    // For ProcessLifecycleOwner
    implementation "android.arch.lifecycle:extensions:$lifecycle_version"
    ...
    }
    @nisrulz #DCBERLIN18
    

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37. ProcessLifecycleOwner
    ON_CREATE
    ON_START & ON_RESUME
    ON_PAUSE & ON_STOP
    ON_DESTROY
    @nisrulz #DCBERLIN18
    

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38. ProcessLifecycleOwner
    ON_CREATE (Only 1 time)
    ON_START & ON_RESUME
    ON_PAUSE & ON_STOP
    ON_DESTROY
    @nisrulz #DCBERLIN18
    

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39. ProcessLifecycleOwner
    ON_CREATE (Only 1 time)
    ON_START & ON_RESUME (First Activity pass)
    ON_PAUSE & ON_STOP
    ON_DESTROY
    @nisrulz #DCBERLIN18
    

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40. ProcessLifecycleOwner
    ON_CREATE (Only 1 time)
    ON_START & ON_RESUME (First Activity pass)
    ON_PAUSE & ON_STOP (after 700ms delay)
    ON_DESTROY
    @nisrulz #DCBERLIN18
    

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41. ProcessLifecycleOwner
    ON_CREATE (Only 1 time)
    ON_START & ON_RESUME (First Activity pass)
    ON_PAUSE & ON_STOP (after 700ms delay)
    ON_DESTROY
    @nisrulz #DCBERLIN18
    

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42. ProcessLifecycleOwner
    ON_CREATE (Only 1 time)
    ON_START & ON_RESUME (First Activity pass)
    ON_PAUSE & ON_STOP (after 700ms delay)
    ON_DESTROY
    @nisrulz #DCBERLIN18
    

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43. ProcessLifecycleOwner
    ON_PAUSE & ON_STOP (after 700ms delay)
    @nisrulz #DCBERLIN18
    

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44. ProcessLifecycleOwner
    ON_PAUSE & ON_STOP (after 700ms delay)
    // Source code
    public class ProcessLifecycleOwner implements LifecycleOwner {
    static final long TIMEOUT_MS = 700; //mls
    ...
    }
    @nisrulz #DCBERLIN18
    

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45. ProcessLifecycleOwner
    Guarantee that ProcessLifecycleOwner won’t send
    any events if activities are
    - Destroyed
    - Recreated due to configuration change
    @nisrulz #DCBERLIN18
    

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46. ProcessLifecycleOwner
    Comes with cost:
    @nisrulz #DCBERLIN18
    

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47. ProcessLifecycleOwner
    Comes with cost:
    extension artifact automatically adds
    element to your manifest
    @nisrulz #DCBERLIN18
    

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48. ProcessLifecycleOwner
    
    
    ...
    android:name="android.arch.lifecycle.ProcessLifecycleOwnerInitializer"
    android:authorities="com.example.app.lifecycle-trojan"
    android:exported="false"
    android:multiprocess="true" />
    
    
    @nisrulz #DCBERLIN18
    

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49. ProcessLifecycleOwner
    // Source code
    // Internal class to initialize Lifecycles.
    public class ProcessLifecycleOwnerInitializer extends ContentProvider {
    @Override
    public boolean onCreate() {
    ...
    ProcessLifecycleOwner.init(getContext());
    return true;
    }
    ...
    }
    @nisrulz #DCBERLIN18
    

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50. ProcessLifecycleOwner
    Side-effect:
    @nisrulz #DCBERLIN18
    

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51. ProcessLifecycleOwner
    Side-effect:
    Inits ProcessLifecycleOwner even if your app
    does not use it!
    @nisrulz #DCBERLIN18
    

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52. ProcessLifecycleOwner
    Side-effect:
    Inits ProcessLifecycleOwner even if your app
    does not use it!
    Why?
    @nisrulz #DCBERLIN18
    

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53. 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
    @nisrulz #DCBERLIN18
    

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54. @nisrulz #DCBERLIN18
    Application.ActivityLifecycleCallback
    vs
    ProcessLifecycleOwner
    

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55. @nisrulz #DCBERLIN18
    Application.ActivityLifecycleCallback
    vs or
    ProcessLifecycleOwner
    

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56. Application.ActivityLifecycleCallback
    // Source code
    public interface ActivityLifecycleCallbacks {
    void onActivityCreated(Activity var1, Bundle var2);
    ...
    void onActivitySaveInstanceState(Activity var1, Bundle var2);
    void onActivityDestroyed(Activity var1);
    }
    @nisrulz #DCBERLIN18
    

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57. Application.ActivityLifecycleCallback
    // Register for the callback
    application
    .registerActivityLifecycleCallbacks(object:
    Application.ActivityLifecycleCallbacks{
    override fun onActivityCreated(activity: Activity?, bundle: Bundle?) {}
    ...
    })
    @nisrulz #DCBERLIN18
    

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58. 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) { .. }
    ...
    });
    }
    }
    @nisrulz #DCBERLIN18
    

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59. 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) { .. }
    ...
    });
    }
    }
    @nisrulz #DCBERLIN18
    

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60. 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) { .. }
    ...
    });
    }
    }
    @nisrulz #DCBERLIN18
    

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61. ProcessLifecycleOwner
    // Source code
    class EmptyActivityLifecycleCallbacks
    implements Application.ActivityLifecycleCallbacks {
    @Override
    public void onActivityCreated(Activity activity,
    Bundle savedInstanceState) {
    //Empty method body
    }
    ...
    }
    @nisrulz #DCBERLIN18
    

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62. ProcessLifecycleOwner
    // Source code
    class EmptyActivityLifecycleCallbacks
    implements Application.ActivityLifecycleCallbacks {
    @Override
    public void onActivityCreated(Activity activity,
    Bundle savedInstanceState) {
    //Empty method body
    }
    ...
    }
    @nisrulz #DCBERLIN18
    

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63. LifecycleRegistry
    @nisrulz #DCBERLIN18
    

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64. LifecycleRegistry
    Implementation of Lifecycle that can handle
    multiple observers
    @nisrulz #DCBERLIN18
    

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65. LifecycleRegistry
    Implementation of Lifecycle that can handle
    multiple observers
    // Source code
    public class LifecycleRegistry extends Lifecycle {
    ...
    }
    @nisrulz #DCBERLIN18
    

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66. LifecycleRegistry
    Implementation of Lifecycle that can handle
    multiple observers
    // Source code
    public class LifecycleRegistry extends Lifecycle {
    ...
    }
    However, you need to dispatch the events yourself.
    @nisrulz #DCBERLIN18
    

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67. 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)
    }
    }
    @nisrulz #DCBERLIN18
    

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68. 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)
    }
    }
    @nisrulz #DCBERLIN18
    

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69. 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)
    }
    }
    @nisrulz #DCBERLIN18
    

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70. 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)
    }
    }
    @nisrulz #DCBERLIN18
    

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71. 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)
    }
    }
    @nisrulz #DCBERLIN18
    

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72. LifecycleRegistry
    val myLifecycleOwner = MyLifecycleOwner()
    // Missing myLifecycleObserver
    // Add lifecycle observer
    myLifecycleOwner.lifecycle.addObserver(myLifecycleObserver)
    // Remove lifecycle observer
    myLifecycleOwner.lifecycle.removeObserver(myLifecycleObserver)
    @nisrulz #DCBERLIN18
    

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73. LifecycleObserver
    @nisrulz #DCBERLIN18
    

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74. LifecycleObserver
    An interface for observing a Lifecycle
    // Source code
    public interface LifecycleObserver {
    // Empty
    }
    @nisrulz #DCBERLIN18
    

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75. LifecycleObserver
    Two ways to implement
    - Annotation
    - Callback Interface
    @nisrulz #DCBERLIN18
    

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76. LifecycleObserver
    dependencies {
    def lifecycle_version = "1.1.1"
    // For Annotation Support
    annotationProcessor "android.arch.lifecycle:compiler:$lifecycle_version"
    ...
    }
    @nisrulz #DCBERLIN18
    

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77. 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() {}
    }
    @nisrulz #DCBERLIN18
    

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78. LifecycleObserver
    val myLifecycleOwner = MyLifecycleOwner()
    // Add lifecycle observer
    myLifecycleOwner.lifecycle.addObserver(myLifecycleObserver)
    // Remove lifecycle observer
    myLifecycleOwner.lifecycle.removeObserver(myLifecycleObserver)
    @nisrulz #DCBERLIN18
    

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79. LifecycleObserver
    val myLifecycleOwner = MyLifecycleOwner()
    val myLifecycleObserver = MyLifecycleObserver()
    // Add lifecycle observer
    myLifecycleOwner.lifecycle.addObserver(myLifecycleObserver)
    // Remove lifecycle observer
    myLifecycleOwner.lifecycle.removeObserver(myLifecycleObserver)
    @nisrulz #DCBERLIN18
    

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80. LifecycleObserver
    val myLifecycleOwner = MyLifecycleOwner()
    val myLifecycleObserver = MyLifecycleObserver()
    // Add lifecycle observer
    myLifecycleOwner.lifecycle.addObserver(myLifecycleObserver)
    // Remove lifecycle observer
    myLifecycleOwner.lifecycle.removeObserver(myLifecycleObserver)
    @nisrulz #DCBERLIN18
    

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81. DefaultLifecycleObserver
    @nisrulz #DCBERLIN18
    

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82. DefaultLifecycleObserver
    Callback interface for listening to
    LifecycleOwner state changes.
    @nisrulz #DCBERLIN18
    

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83. DefaultLifecycleObserver
    Callback interface for listening to
    LifecycleOwner state changes.
    Recommended over annotations if using Java 8
    language.
    @nisrulz #DCBERLIN18
    

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84. 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"
    ...
    }
    @nisrulz #DCBERLIN18
    

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85. DefaultLifecycleObserver
    // Source code
    public interface DefaultLifecycleObserver extends FullLifecycleObserver {
    @Override
    default void onCreate(@NonNull LifecycleOwner owner) { ... }
    ...
    @Override
    default void onDestroy(@NonNull LifecycleOwner owner) { ... }
    }
    @nisrulz #DCBERLIN18
    

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86. DefaultLifecycleObserver
    // Source code
    interface FullLifecycleObserver extends LifecycleObserver {
    void onCreate(LifecycleOwner owner);
    void onStart(LifecycleOwner owner);
    ...
    void onDestroy(LifecycleOwner owner);
    }
    @nisrulz #DCBERLIN18
    

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87. DefaultLifecycleObserver
    class MyLifecycleObserver : DefaultLifecycleObserver {
    override fun onCreate(owner: LifecycleOwner) {}
    ...
    override fun onDestroy(owner: LifecycleOwner) {}
    }
    @nisrulz #DCBERLIN18
    

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88. LiveData
    @nisrulz #DCBERLIN18
    

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89. LiveData
    A lifecycle aware base class for
    encapsulating loading data
    @nisrulz #DCBERLIN18
    

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90. LiveData
    A lifecycle aware base class for
    encapsulating loading data
    Lightweight implementation of Observer
    pattern
    @nisrulz #DCBERLIN18
    

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91. LiveData
    dependencies {
    def lifecycle_version = "1.1.1"
    // For LiveData
    implementation "android.arch.lifecycle:livedata:$lifecycle_version"
    ...
    }
    @nisrulz #DCBERLIN18
    

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92. LiveData
    // Source Code
    public abstract class LiveData {
    ...
    protected void postValue(T value) {...}
    ...
    @MainThread
    protected void setValue(T value) {...}
    ...
    protected void onActive() {...}
    protected void onInactive() {...}
    }
    @nisrulz #DCBERLIN18
    

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93. LiveData
    // Source Code
    public abstract class LiveData {
    ...
    protected void postValue(T value) {...} // Sets the value async
    ...
    @MainThread
    protected void setValue(T value) {...}
    ...
    protected void onActive() {...}
    protected void onInactive() {...}
    }
    @nisrulz #DCBERLIN18
    

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94. LiveData
    // Source Code
    public abstract class LiveData {
    ...
    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() {...}
    }
    @nisrulz #DCBERLIN18
    

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95. LiveData
    // Source Code
    public abstract class LiveData {
    ...
    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() {...}
    }
    @nisrulz #DCBERLIN18
    

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96. LiveData
    // Source Code
    public abstract class LiveData {
    ...
    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
    }
    @nisrulz #DCBERLIN18
    

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97. LiveData
    class MySensorLiveData(context: Context?) : LiveData() {
    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))
    }
    ...
    }
    }
    @nisrulz #DCBERLIN18
    

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98. LiveData
    class MySensorLiveData(context: Context?) : LiveData() {
    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))
    }
    ...
    }
    }
    @nisrulz #DCBERLIN18
    

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99. LiveData
    class MySensorLiveData(context: Context?) : LiveData() {
    ...
    override fun onActive() {
    ...
    sensorManager?.registerListener(sensorListener,
    sensorManager.getDefaultSensor(Sensor.TYPE_ACCELEROMETER),
    SensorManager.SENSOR_DELAY_FASTEST)
    }
    override fun onInactive() {
    ...
    sensorManager.unregisterListener(sensorListener)
    }
    }
    @nisrulz #DCBERLIN18
    

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100. LiveData
     class MySensorLiveData(context: Context?) : LiveData() {
     ...
     override fun onActive() {
     ...
     sensorManager?.registerListener(sensorListener,
     sensorManager.getDefaultSensor(Sensor.TYPE_ACCELEROMETER),
     SensorManager.SENSOR_DELAY_FASTEST)
     }
     override fun onInactive() {
     ...
     sensorManager.unregisterListener(sensorListener)
     }
     }
     @nisrulz #DCBERLIN18
     

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101. LiveData
     val mySensorLiveData = MySensorLiveData(this)
     // Observe for values
     mySensorLiveData.observe(this, Observer{ floatVal ->
     // Update the UI
     })
     @nisrulz #DCBERLIN18
     

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102. ViewModel
     @nisrulz #DCBERLIN18
     

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103. ViewModel
     - Hold & manage UI related
     data in Lifecycle
     conscious way
     - Survives configuration
     changes
     - Prevents unnecessary
     reloading of data
     @nisrulz #DCBERLIN18
     

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104. ViewModel
     dependencies {
     def lifecycle_version = "1.1.1"
     // For ViewModel
     implementation "android.arch.lifecycle:viewmodel:$lifecycle_version"
     ...
     }
     @nisrulz #DCBERLIN18
     

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105. ViewModel
     // Source code
     public abstract class ViewModel {
     // Called when ViewModel is destroyed
     protected void onCleared() {
     }
     }
     @nisrulz #DCBERLIN18
     

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106. ViewModel
     class MyViewModel : ViewModel() {
     private val username = MutableLiveData()
     fun initExpensiveOperation() {
     // expensive operation, e.g. network request
     username.value = "Nishant" // username.setValue(“Nishant”)
     }
     fun getUsername(): LiveData {
     return username
     }
     }
     @nisrulz #DCBERLIN18
     

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107. ViewModel
     class MyViewModel : ViewModel() {
     private val username = MutableLiveData()
     fun initExpensiveOperation() {
     // expensive operation, e.g. network request
     username.value = "Nishant" // username.setValue(“Nishant”)
     }
     fun getUsername(): LiveData {
     return username
     }
     }
     @nisrulz #DCBERLIN18
     

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108. ViewModel
     class MyViewModel : ViewModel() {
     private val username = MutableLiveData()
     fun initExpensiveOperation() {
     // expensive operation, e.g. network request
     username.value = "Nishant" // username.setValue(“Nishant”)
     }
     fun getUsername(): LiveData {
     return username
     }
     }
     @nisrulz #DCBERLIN18
     

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109. ViewModel
     class MyViewModel : ViewModel() {
     private val username = MutableLiveData()
     fun initExpensiveOperation() {
     // expensive operation, e.g. network request
     username.value = "Nishant" // username.setValue(“Nishant”)
     }
     fun getUsername(): LiveData {
     return username
     }
     }
     @nisrulz #DCBERLIN18
     

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110. ViewModel
     class MyViewModel : ViewModel() {
     private val username = MutableLiveData()
     fun initExpensiveOperation() {
     // expensive operation, e.g. network request
     username.value = "Nishant" // username.setValue(“Nishant”)
     }
     fun getUsername(): LiveData {
     return username
     }
     }
     @nisrulz #DCBERLIN18
     

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111. ViewModel
     class MyViewModel : ViewModel() {
     private val username = MutableLiveData()
     fun initExpensiveOperation() {
     // expensive operation, e.g. network request
     username.value = "Nishant" // username.setValue(“Nishant”)
     }
     fun getUsername(): LiveData {
     return username
     }
     }
     @nisrulz #DCBERLIN18
     

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112. ViewModel
     val viewModel = ViewModelProviders
     .of(this)
     .get(MyViewModel::class.java)
     viewModel.getUsername().observe(this, Observer { text ->
     //Update the UI
     })
     @nisrulz #DCBERLIN18
     

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113. ViewModel
     val viewModel = ViewModelProviders
     .of(this)
     .get(MyViewModel::class.java)
     viewModel.getUsername().observe(this, Observer { text ->
     //Update the UI
     })
     @nisrulz #DCBERLIN18
     

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114. Thank You
     twitter.com/nisrulz
     github.com/nisrulz
     www.nisrulz.com
     

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115. More Info
     Is your Android Library, Lifecycle-Aware?
     https://android.jlelse.eu/is-your-android-library-lifecycle-aware-127629d32dcc
     Official documentation about lifecycle components
     d.android.com/topic/libraries/architecture/lifecycle
     Using ProcessLifecycleOwner for libraries example
     https://github.com/nisrulz/android-examples/tree/develop/UsingProcessLifecycleOwnerForLibs
     Using Lifecycle Components for libraries example
     https://github.com/nisrulz/android-examples/tree/develop/LifeCycleCompForLib
     @nisrulz #DCBERLIN18
     

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116. The A,B and C
     of
     Lifecycle Components
     twitter.com/nisrulz
     github.com/nisrulz
     www.nisrulz.com
     

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