Inside LifecycleObserver

How to handle components' lifecycle in Android app developing.

Transcript

1. Hiroyuki Mori
   @moridroid
   Inside LifecycleObserver
   

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2. Lifecycle Problems
   in Android
   

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3. in early days
   https://developer.android.com/guide/components/activities/activity-lifecycle.html
   

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4. today
   Steve Pomeroy https://github.com/xxv/android-lifecycle　CC-BY-SA 4.0
   

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5. case 1:
   fetching data every onCreate
   

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6. case 1:
   fetching data every onCreate
   

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7. case 1:
   fetching data every onCreate
   

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8. case 1:
   fetching data every onCreate
   

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9. case 1:
   fetching data every onCreate
   

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10. case 1:
    fetching data every onCreate
    Wasteful
    

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11. case 2:
    showing after activity’s death
    

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12. case 2:
    showing after activity’s death
    

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13. case 2:
    showing after activity’s death
    

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14. case 2:
    showing after activity’s death
    Crash !!
    

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15. case 3:
    forgetting to stop observing
    

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16. case 3:
    forgetting to stop observing
    

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17. case 3:
    forgetting to stop observing
    

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18. case 3:
    forgetting to stop observing
    memory
    leak
    

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19. Handling lifecycles
    

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20. Lifecycle library
    

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21. Observer pattern
    

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28. ×
    

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32. loose coupled
    

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35. Event Channel
    

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37. notify events
    

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38. observe
    

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40. Inside Lifecycle library
    

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41. subscribing lifecycle events
    

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42. class MainActivity : AppCompatActivity() {
    override fun onCreate(savedInstanceState: Bundle?) {
    　　...
    lifecycle.addObserver(yourObservable)
    }
    }
    

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43. public class LifecycleRegistry extends Lifecycle {
    @Override
    public void addObserver(@NonNull LifecycleObserver observer) {
    State initialState = mState == DESTROYED ? DESTROYED : INITIALIZED;
    ObserverWithState statefulObserver
    = new ObserverWithState(observer, initialState);
    ObserverWithState previous
    = mObserverMap.putIfAbsent(observer, statefulObserver);
    

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44. public class LifecycleRegistry extends Lifecycle {
    @Override
    public void addObserver(@NonNull LifecycleObserver observer) {
    State initialState = mState == DESTROYED ? DESTROYED : INITIALIZED;
    ObserverWithState statefulObserver
    = new ObserverWithState(observer, initialState);
    ObserverWithState previous
    = mObserverMap.putIfAbsent(observer, statefulObserver);
    

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45. static class ObserverWithState {
    ...
    ObserverWithState(LifecycleObserver observer, State initialState) {
    mLifecycleObserver = Lifecycling.getCallback(observer);
    ...
    }
    void dispatchEvent(LifecycleOwner owner, Event event) {
    ...
    mLifecycleObserver.onStateChanged(owner, event);
    ...
    }
    }
    

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46. static class ObserverWithState {
    ...
    ObserverWithState(LifecycleObserver observer, State initialState) {
    mLifecycleObserver = Lifecycling.getCallback(observer);
    ...
    }
    void dispatchEvent(LifecycleOwner owner, Event event) {
    ...
    mLifecycleObserver.onStateChanged(owner, event);
    ...
    }
    }
    

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47. publishing lifecycle events
    

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48. public class SupportActivity extends Activity implements LifecycleOwner {
    ...
    protected void onCreate(@Nullable Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    ReportFragment.injectIfNeededIn(this);
    }
    ...
    }
    

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49. public class ReportFragment extends Fragment {
    ...
    public void onActivityCreated(Bundle savedInstanceState) {
    dispatch(Lifecycle.Event.ON_CREATE);
    }
    public void onStart() {
    dispatch(Lifecycle.Event.ON_START);
    }
    public void onResume() {
    dispatch(Lifecycle.Event.ON_RESUME);
    }
    public void onPause() {
    dispatch(Lifecycle.Event.ON_PAUSE);
    }
    public void onStop() {
    dispatch(Lifecycle.Event.ON_STOP);
    }
    ...
    }
    

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50. public class ReportFragment extends Fragment {
    ...
    private void dispatch(Lifecycle.Event event) {
    ...
    if (activity instanceof LifecycleOwner) {
    Lifecycle lifecycle = ((LifecycleOwner) activity).getLifecycle();
    if (lifecycle instanceof LifecycleRegistry) {
    ((LifecycleRegistry) lifecycle).handleLifecycleEvent(event);
    }
    }
    }
    }
    

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51. ObserverWithState
    AdapterObserver
    Adapter
    FooObserver
    ReportFragment
    SupportActivity
    LifecycleRegistry
    addObserver
    attach
    dispatch event
    sync
    

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52. ReportFragment
    SupportActivity
    LifecycleRegistry
    attach
    dispatch event
    

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53. FooObserver
    ReportFragment
    SupportActivity
    LifecycleRegistry
    addObserver
    attach
    dispatch event
    

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54. ObserverWithState
    AdapterObserver
    Adapter
    FooObserver
    ReportFragment
    SupportActivity
    LifecycleRegistry
    addObserver
    attach
    dispatch event
    sync
    

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55. Subscriber
    Publisher
    EventChannel
    subscribe
    publish event
    fire event
    

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56. How to use
    

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57. example:
    Observing network state
    

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60. without LifecycleObserver
    

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61. class NetworkStateReceiver(private val callback : (NetworkInfo?) -> Unit) : BroadcastReceiver() {
    override fun onReceive(context: Context?, intent: Intent?) {
    val conn = context?.getSystemService(ConnectivityManager::class.java) ?: return
    callback(conn.activeNetworkInfo)
    }
    }
    Step1 : Create a BroadcastReceiver
    

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62. receiver = NetworkStateReceiver {
    if (it != null && it.isConnected) {
    textView.text = "online"
    } else {
    textView.text = "offline"
    }
    }
    Step2 : create an instance
    create an instance
    

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63. Step3 : register it at onResume
    override fun onResume() {
    super.onResume()
    val filter = IntentFilter(ConnectivityManager.CONNECTIVITY_ACTION)
    registerReceiver(receiver, filter)
    }
    register at onResume
    

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64. override fun onPause() {
    super.onPause()
    unregisterReceiver(receiver)
    }
    Step4 : unregister it at onPause
    unregister at onPause
    

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65. override fun onPause() {
    super.onPause()
    unregisterReceiver(receiver)
    }
    Step5 : Never forget to unregister
    unregister at onPause
    Don’t miss it
    

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66. with LifecycleObserver
    

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67. enum class Connectivity { OFFLINE, ONLINE }
    class NetworkObservable(
    private var activity: Activity?,
    private val callback : (Connectivity) -> Unit) : LifecycleObserver {
    private val receiver = NetworkStateReceiver {
    if (it != null && it.isConnected) {
    callback(Connectivity.ONLINE)
    } else {
    callback(Connectivity.OFFLINE)
    }
    }
    }
    Step1 : Wrap the receiver
    

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68. enum class Connectivity { OFFLINE, ONLINE }
    class NetworkObservable(
    private var activity: Activity?,
    private val callback : (Connectivity) -> Unit) : LifecycleObserver {
    private val receiver = NetworkStateReceiver {
    if (it != null && it.isConnected) {
    callback(Connectivity.ONLINE)
    } else {
    callback(Connectivity.OFFLINE)
    }
    }
    }
    Step1 : Wrap the receiver
    implements
    LifecycleObserver
    

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69. @OnLifecycleEvent(Lifecycle.Event.ON_RESUME)
    fun registerReceiver() {
    activity?.registerReceiver(receiver, IntentFilter(ConnectivityManager.CONNECTIVITY_ACTION))
    }
    @OnLifecycleEvent(Lifecycle.Event.ON_PAUSE)
    fun unregisterReceiver() {
    activity?.unregisterReceiver(receiver)
    }
    @OnLifecycleEvent(Lifecycle.Event.ON_DESTROY)
    fun release() {
    activity = null
    }
    Step2 : register / unregister at lifecycle events
    

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70. @OnLifecycleEvent(Lifecycle.Event.ON_RESUME)
    fun registerReceiver() {
    activity?.registerReceiver(receiver, IntentFilter(ConnectivityManager.CONNECTIVITY_ACTION))
    }
    @OnLifecycleEvent(Lifecycle.Event.ON_PAUSE)
    fun unregisterReceiver() {
    activity?.unregisterReceiver(receiver)
    }
    @OnLifecycleEvent(Lifecycle.Event.ON_DESTROY)
    fun release() {
    activity = null
    }
    Step2 : register / unregister at lifecycle events
    @OnLifecycleEvent
    

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71. class MainActivity : AppCompatActivity() {
    override fun onCreate(savedInstanceState: Bundle?) {
    ...
    lifecycle.addObserver( NetworkObservable(this) {
    if (it == Connectivity.ONLINE) {
    textView.text = "online"
    } else {
    textView.text = "offline"
    }
    })
    }
    }
    Step3 : Use it !
    

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72. class MainActivity : AppCompatActivity() {
    override fun onCreate(savedInstanceState: Bundle?) {
    ...
    lifecycle.addObserver( NetworkObservable(this) {
    if (it == Connectivity.ONLINE) {
    textView.text = "online"
    } else {
    textView.text = "offline"
    }
    })
    }
    }
    Step3 : Use it !
    easy to use
    

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73. Conclusion
    

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74. Lifecycle Management
    

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75. Lifecycle Management
    - is a hard and hassle task
    

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76. Lifecycle Management
    - is a hard and hassle task
    - can cause problems
    

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77. Lifecycle Management
    - is a hard and hassle task
    - can cause problems
    The Lifecycle library
    

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78. Lifecycle Management
    - is a hard and hassle task
    - can cause problems
    The Lifecycle library
    - provides the feature to observe lifecycles
    

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79. Lifecycle Management
    - is a hard and hassle task
    - can cause problems
    The Lifecycle library
    - provides the feature to observe lifecycles
    - can create lifecycle-aware components easily
    

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80. Hiroyuki Mori
    @moridroid
    Thank you
    

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