Android Volley tidak menyimpan gambar dalam cache

Saya menggunakan ini tutorial untuk menampilkan dan menyimpan gambar dalam grid menggunakan Volley. ketika internet terhubung, itu berfungsi dengan baik. tetapi setelah terputus, gambar tidak muncul. sepertinya Volley tidak menyimpan gambar apa pun dalam cache. Masalahnya, belum ada dokumentasi lengkap tentang caching image menggunakan Volley. Ini kode saya:

xml:

<android.support.v4.widget.DrawerLayout
xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
xmlns:tools="http://schemas.android.com/tools"
android:id="@+id/drawer_layout"
android:layout_width="match_parent"
android:layout_height="match_parent">

<LinearLayout
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical">

    <LinearLayout
        android:id="@+id/container_toolbar"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:orientation="vertical">

        <include
            android:id="@+id/toolbar"
            layout="@layout/toolbar" />
    </LinearLayout>


    <RelativeLayout
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:background="#F4F4F6"
        android:paddingTop="@dimen/activity_vertical_margin"
        tools:context=".Content_Gallery_Activity">

        <TextView
            android:id="@+id/text_gallery_title"
            android:layout_width="fill_parent"
            android:layout_height="wrap_content"
            android:layout_alignParentTop="true"
            android:layout_centerHorizontal="true"
            android:gravity="center"
            android:paddingLeft="10dp"
            android:paddingRight="10dp"
            android:textAppearance="?android:attr/textAppearanceSmall" />

        <RelativeLayout
            android:id="@+id/relative_gallery"
            android:layout_width="match_parent"
            android:layout_height="80dp"
            android:layout_below="@+id/text_gallery_title"
            android:layout_marginLeft="8dp"
            android:layout_marginRight="8dp"
            android:layout_marginTop="10dp"
            android:background="@drawable/rect_lst_tree"
            android:paddingLeft="10dp"
            android:paddingRight="10dp" >

            <com.beardedhen.androidbootstrap.AwesomeTextView
                android:id="@+id/font_time"
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:layout_centerVertical="true"
                android:layout_toLeftOf="@+id/tv_date_gallery"
                app:bootstrapBrand="info"
                app:fontAwesomeIcon="fa_clock_o"
                >
            </com.beardedhen.androidbootstrap.AwesomeTextView>

            <TextView
                android:id="@+id/tv_date_gallery"
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:layout_alignParentRight="true"
                android:layout_centerVertical="true"
                android:layout_marginLeft="5dp"
                android:textAppearance="?android:attr/textAppearanceSmall"
                android:textColor="#1B131B"
                android:textSize="13dp" >
            </TextView>

            <TextView
                android:id="@+id/text_image_count"
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:layout_centerVertical="true"
                android:layout_marginLeft="10dp"
                android:layout_toRightOf="@+id/gallery_thumb"
                android:text="Small"
                android:textAppearance="?android:attr/textAppearanceSmall"
                android:textColor="#F01435"
                android:textSize="12dp" />

            <ir.whc.news.views.CircularNetworkImageView
                android:id="@+id/gallery_thumb"
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:layout_alignParentLeft="true"
                android:layout_centerVertical="true"
                >
            </ir.whc.news.views.CircularNetworkImageView>
        </RelativeLayout>

        <GridView
            android:id="@+id/gridView1"
            android:layout_width="match_parent"
            android:layout_height="fill_parent"
            android:layout_below="@+id/relative_gallery"
            android:columnWidth="100dp"
            android:horizontalSpacing="1dp"
            android:numColumns="auto_fit"
            android:paddingTop="10dp"
            android:stretchMode="spacingWidthUniform"
            android:verticalSpacing="8dp" >
        </GridView>

    </RelativeLayout>
</LinearLayout>


<fragment
    android:id="@+id/fragment_navigation_drawer"
    android:name="ir.whc.news.activity.FragmentDrawer"
    android:layout_width="@dimen/nav_drawer_width"
    android:layout_height="match_parent"
    android:layout_gravity="start"
    app:layout="@layout/fragment_navigation_drawer"
    tools:layout="@layout/fragment_navigation_drawer" />

Actitvity:

    grd.setAdapter(new MyImageAdapter(galleryItem.get_images()));
        grd.setOnItemClickListener(new AdapterView.OnItemClickListener() {
            @Override
            public void onItemClick(AdapterView<?> parent, View view, int position, long id) {
                Intent intent = new Intent(ContentGalleryActivity.this, DisplayImageActivity.class);
                intent.putExtra("largimage_url", galleryItem.get_images().get(position).get_largimage_path());
                startActivity(intent);
            }
        });

adaptor:

    class MyImageAdapter extends BaseAdapter {

        ArrayList<ImageItem> imageItems;

        public MyImageAdapter(ArrayList<ImageItem> imageItems)
        {
            this.imageItems=imageItems;
        }

        @Override
        public int getCount() {
            return imageItems.size();
        }

        @Override
        public Object getItem(int position) {
            return imageItems.get(position);
        }

        @Override
        public long getItemId(int position) {
            return imageItems.get(position).get_id();
        }

        @Override
        public View getView(int position, View convertView, ViewGroup parent) {

            View view = convertView;
            final ViewHolder gridViewImageHolder;
//            check to see if we have a view
            if (view == null) {
                view = getLayoutInflater().inflate(R.layout.grid_image_item, parent, false);
                gridViewImageHolder = new ViewHolder();
                gridViewImageHolder.imageView = (ImageView) view.findViewById(R.id.image_grid_networkImageView);
                view.setTag(gridViewImageHolder);
            } else {
                gridViewImageHolder = (ViewHolder) view.getTag();
            }

            mNetworkImageView = (NetworkImageView) gridViewImageHolder.imageView;
            mNetworkImageView.setDefaultImageResId(R.drawable.ic_launcher);
            mNetworkImageView.setErrorImageResId(android.R.drawable.ic_dialog_alert);
            mNetworkImageView.setAdjustViewBounds(true);
            mNetworkImageView.setImageUrl(imageItems.get(position).get_thumb_path(), imageLoader);

            return view;
        }
    }

Pembuat gambar:

imageLoader = MyApplication.getInstance().getImageLoader();
        imageLoader.get(galleryItem.get_imgPath(), imageLoader.getImageListener(img_thumb,
                R.drawable.ic_launcher,
                android.R.drawable.ic_dialog_alert));
        img_thumb.setImageUrl(galleryItem.get_imgPath(), imageLoader);

LruBitmapCache:

import android.graphics.Bitmap;
import android.support.v4.util.LruCache;

import com.android.volley.toolbox.ImageLoader.ImageCache;

public class LruBitmapCache extends LruCache<String, Bitmap> implements
        ImageCache {
    public static int getDefaultLruCacheSize() {
        final int maxMemory = (int) (Runtime.getRuntime().maxMemory() / 1024);
        final int cacheSize = maxMemory / 8;

        return cacheSize;
    }

    public LruBitmapCache() {
        this(getDefaultLruCacheSize());
    }

    public LruBitmapCache(int sizeInKiloBytes) {
        super(sizeInKiloBytes);
    }

    @Override
    protected int sizeOf(String key, Bitmap value) {
        return value.getRowBytes() * value.getHeight() / 1024;
    }

    @Override
    public Bitmap getBitmap(String url) {
        return get(url);
    }

    @Override
    public void putBitmap(String url, Bitmap bitmap) {
        put(url, bitmap);
    }
}

apa yang salah dengan kode saya. Saya lelah berjuang.