A Folio Page that supports using Glide

FolioGlidePage

import android.support.annotation.StringRes;
import android.support.v7.widget.Toolbar;
import android.view.Menu;
import android.view.MenuInflater;
import android.view.MenuItem;

import com.bumptech.glide.RequestManager;
import com.bumptech.glide.manager.Lifecycle;
import com.bumptech.glide.manager.LifecycleListener;
import com.bumptech.glide.manager.RequestManagerTreeNode;
import com.bumptech.glide.util.Util;
import com.umaplay.android.App;
import com.umaplay.folio.Page;

import java.util.Collections;
import java.util.HashSet;
import java.util.Set;
import java.util.WeakHashMap;


public abstract class FolioGlidePage extends Page implements Lifecycle {
    private final Set<LifecycleListener> mGlideLifecycleListeners =
            Collections.newSetFromMap(new WeakHashMap<LifecycleListener, Boolean>());
    private RequestManager mGlideInstance;
    private boolean isStarted;
    private boolean isDestroyed;

    public RequestManager getGlide() {
        if(mGlideInstance == null) {
            mGlideInstance = new RequestManager(getContext(), this, new RequestManagerTreeNode() {

                public Set<RequestManager> descendants = new HashSet<>();

                @Override
                public Set<RequestManager> getDescendants() {
                    return descendants;
                }
            });
        }

        return mGlideInstance;
    }

    /**
     * Adds the given listener to the list of listeners to be notified on each lifecycle event.
     *
     * <p> The latest lifecycle event will be called on the given listener synchronously in this
     * method. If the activity or fragment is stopped, {@link LifecycleListener#onStop()}} will be
     * called, and same for onStart and onDestroy. </p>
     *
     * <p> Note - {@link com.bumptech.glide.manager.LifecycleListener}s that are added more than once
     * will have their lifecycle methods called more than once. It is the caller's responsibility to
     * avoid adding listeners multiple times. </p>
     */
    @Override
    public void addListener(LifecycleListener listener) {
        mGlideLifecycleListeners.add(listener);

        if (isDestroyed) {
            listener.onDestroy();
        } else if (isStarted) {
            listener.onStart();
        } else {
            listener.onStop();
        }
    }

    @Override
    public void onPageIsVisible() {
        super.onPageIsVisible();

        isStarted = true;
        for (LifecycleListener lifecycleListener : Util.getSnapshot(mGlideLifecycleListeners)) {
            lifecycleListener.onStart();
        }
    }


    @Override
    public void onPageIsInvisible() {
        super.onPageIsInvisible();

        isStarted = false;
        for (LifecycleListener lifecycleListener : Util.getSnapshot(mGlideLifecycleListeners)) {
            lifecycleListener.onStop();
        }
    }

    @Override
    public void onDestroy() {
        isDestroyed = true;
        for (LifecycleListener lifecycleListener : Util.getSnapshot(mGlideLifecycleListeners)) {
            lifecycleListener.onDestroy();
        }
        mGlideInstance = null;
        super.onDestroy();

        App.getRefwatcher().watch(this);
    }
}