Lifecycle

1.Lifecycle

Lifecycle ，是被观察者,有addObserver和removeObserver这种添加或者移除观察者的方法

public abstract class Lifecycle {

    AtomicReference<Object> mInternalScopeRef = new AtomicReference<>();
    
    @MainThread
    public abstract void addObserver(@NonNull LifecycleObserver observer);
    
    @MainThread
    public abstract void removeObserver(@NonNull LifecycleObserver observer);
    
    @MainThread
    @NonNull
    public abstract State getCurrentState();

    @SuppressWarnings("WeakerAccess")
    public enum Event {
        ON_CREATE,
        ON_START,
        ON_RESUME,
        ON_PAUSE,
        ON_STOP,
        ON_DESTROY,
        ON_ANY
    }

    /**
     * Lifecycle states. You can consider the states as the nodes in a graph and
     * {@link Event}s as the edges between these nodes.
     */
    @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;
        }
    }
}

2.LifecycleObserver

LifecycleObserver是观察者

public interface LifecycleObserver {

}

3.LifecycleOwner

LifecycleOwner是只有一个方法getLifecycle()的接口，是让拥有生命周期的东西实现比如（activity）用来获取Lifecycle。在Android Support Library 26.1.0 及其之后已经activity 和 fragment 已经默认实现了LifecycleOwner 所以在 activity 里我们可以直接：

getLifecycle().addObserver(new LocationListener());

这样我们的LocationListener就会感知 activity 的生命周期了

public interface LifecycleOwner {
    /**
     * Returns the Lifecycle of the provider.
     *
     * @return The lifecycle of the provider.
     */
    @NonNull
    Lifecycle getLifecycle();
}

4.绑定

当需要在activity启动后自动发起定位,退出后自动销毁定位可以这么做

• 观察者

public class LocationListener implements LifecycleObserver {
    @OnLifecycleEvent(Lifecycle.Event.ON_START)
    void startLocation() {
        System.out.println("===startLocation===");
    }

    @OnLifecycleEvent(Lifecycle.Event.ON_STOP)
    void stopLocation() {
        System.out.println("===stopLocation===");
    }
}

• 被观察者 在activity中添加代码

getLifecycle().addObserver(new LocationListener());

这样activity在进去和退出的时候输出日志

11-19 15:08:27.902 1629-1629/test.com.shineextest I/System.out: ===startLocation===
11-19 15:08:31.696 1629-1629/test.com.shineextest I/System.out: ===stopLocation===