Lifecycle

Lifecycle的生命周期状态事件和状态

Lifecycle使用两个枚举来跟踪关联组件的生命周期状态，这两个枚举类分别是Event和State,State代表Lifecycle的生命周期所处的状态，Event代表Lifecycle生命周期所处的事件。

@SuppressWarnings("WeakerAccess")public enum Event {    /**     * Constant for onCreate event of the {@link LifecycleOwner}.     */    ON_CREATE,    /**     * Constant for onStart event of the {@link LifecycleOwner}.     */    ON_START,    /**     * Constant for onResume event of the {@link LifecycleOwner}.     */    ON_RESUME,    /**     * Constant for onPause event of the {@link LifecycleOwner}.     */    ON_PAUSE,    /**     * Constant for onStop event of the {@link LifecycleOwner}.     */    ON_STOP,    /**     * Constant for onDestroy event of the {@link LifecycleOwner}.     */    ON_DESTROY,    /**     * An {@link Event Event} constant that can be used to match all events.     */    ON_ANY}

@SuppressWarnings("WeakerAccess")public enum State {    /**     * Destroyed state for a LifecycleOwner. After this event, this Lifecycle will not dispatch     * any more events. For instance, for an {@link android.app.Activity}, this state is reached     * <b>right before</b> Activity's {@link android.app.Activity#onDestroy() onDestroy} call.     */    DESTROYED,    /**     * Initialized state for a LifecycleOwner. For an {@link android.app.Activity}, this is     * the state when it is constructed but has not received     * {@link android.app.Activity#onCreate(android.os.Bundle) onCreate} yet.     */    INITIALIZED,    /**     * Created state for a LifecycleOwner. For an {@link android.app.Activity}, this state     * is reached in two cases:     * <ul>     *     <li>after {@link android.app.Activity#onCreate(android.os.Bundle) onCreate} call;     *     <li><b>right before</b> {@link android.app.Activity#onStop() onStop} call.     * </ul>     */    CREATED,    /**     * Started state for a LifecycleOwner. For an {@link android.app.Activity}, this state     * is reached in two cases:     * <ul>     *     <li>after {@link android.app.Activity#onStart() onStart} call;     *     <li><b>right before</b> {@link android.app.Activity#onPause() onPause} call.     * </ul>     */    STARTED,    /**     * Resumed state for a LifecycleOwner. For an {@link android.app.Activity}, this state     * is reached after {@link android.app.Activity#onResume() onResume} is called.     */    RESUMED;    /**     * Compares if this State is greater or equal to the given {@code state}.     *     * @param state State to compare with     * @return true if this State is greater or equal to the given {@code state}     */    public boolean isAtLeast(@NonNull State state) {        return compareTo(state) >= 0;    }}Lifeccle是如何观察Activity和Fragment的生命周期在Android 26.1.0版本后的library中Activity和fragment已经默认实现了LifecyclerOwner接口

LifecycleOwner 和 LifecycleRegisterOwner 是继承关系，

LifecycleRegisterOwner extends LifecycleOwner ,不同的是 LifecycleRegisterOwner 的 getLifecycle()方法获取的是  LifecycleRegister，而

LifecycleOwner 的 getLifecycle()方法获取的是 LifecycleActivity

public class ComponentActivity extends androidx.core.app.ComponentActivity implements        LifecycleOwner

@Overrideprotected void onCreate(@Nullable Bundle savedInstanceState) {    super.onCreate(savedInstanceState);    mSavedStateRegistryController.performRestore(savedInstanceState);    ReportFragment.injectIfNeededIn(this);    if (mContentLayoutId != 0) {        setContentView(mContentLayoutId);    }}

在Activity中，生命周期的监听操作都是在 ReportFragment 中完成的

Fragment 

public class Fragment implements ComponentCallbacks, OnCreateContextMenuListener, LifecycleOwner

在Fragment 中，生命周期的监听操作是在

final class FragmentManagerImpl extends FragmentManager

 中完成的