RxActivityLifecycleCallbacks

RxActivityLifecycleCallbacks.java

package rx.android.lifecycle;

import android.app.Activity;
import android.app.Application;
import android.content.Context;
import android.os.Bundle;
import rx.Observable;
import rx.subjects.BehaviorSubject;

import java.util.Map;
import java.util.concurrent.ConcurrentHashMap;

class RxActivityLifecycleCallbacks implements Application.ActivityLifecycleCallbacks {

    private static RxActivityLifecycleCallbacks instance;

    private Map<Activity, BehaviorSubject<LifecycleEvent>> activityBehaviorSubjectMap;

    public static final RxActivityLifecycleCallbacks getInstance(Context context) {
        if (instance == null) {
            instance = new RxActivityLifecycleCallbacks(context);
        }

        return instance;
    }

    private RxActivityLifecycleCallbacks(Context context) {
        activityBehaviorSubjectMap = new ConcurrentHashMap<Activity, BehaviorSubject<LifecycleEvent>>();

        Application application = (Application) context.getApplicationContext();
        application.registerActivityLifecycleCallbacks(this);
    }

    public Observable<LifecycleEvent> getLifecycle(Activity activity) {
        BehaviorSubject<LifecycleEvent> subject = activityBehaviorSubjectMap.get(activity);

        if (subject == null) {
            throw new IllegalStateException("The Activity is outside the lifecycle; cannot bind to it!");
        }

        return subject.asObservable();
    }

    @Override
    public void onActivityCreated(Activity activity, Bundle savedInstanceState) {
        activityBehaviorSubjectMap.put(activity, BehaviorSubject.create(LifecycleEvent.CREATE));
    }

    @Override
    public void onActivityStarted(Activity activity) {
        activityBehaviorSubjectMap.get(activity).onNext(LifecycleEvent.START);
    }

    @Override
    public void onActivityResumed(Activity activity) {
        activityBehaviorSubjectMap.get(activity).onNext(LifecycleEvent.RESUME);
    }

    @Override
    public void onActivityPaused(Activity activity) {
        activityBehaviorSubjectMap.get(activity).onNext(LifecycleEvent.PAUSE);
    }

    @Override
    public void onActivityStopped(Activity activity) {
        activityBehaviorSubjectMap.get(activity).onNext(LifecycleEvent.STOP);
    }

    @Override
    public void onActivityDestroyed(Activity activity) {
        activityBehaviorSubjectMap.remove(activity).onNext(LifecycleEvent.DESTROY);
    }

    @Override
    public void onActivitySaveInstanceState(Activity activity, Bundle outState) {
        // Not tracked
    }
}