Make some methods return the specific InfoItem type

- Some methods were returning a broader range of InfoItem types than it should be. For example, a ChannelInfo should return a List containing only StreamInfoItem, instead of the more general InfoItem.
- Renamed and changed return type of ListExtractor.getInfoItems to getInitialPage returning a InfoItemsPage, to be consistent with getPage(url)

src/main/java/org/schabi/newpipe/extractor/ListExtractor.java

@@ -4,21 +4,45 @@ import org.schabi.newpipe.extractor.exceptions.ExtractionException;
 
 import javax.annotation.Nonnull;
 import java.io.IOException;
+import java.util.Collections;
 import java.util.List;
 
 /**
  * Base class to extractors that have a list (e.g. playlists, users).
  */
-public abstract class ListExtractor extends Extractor {
+public abstract class ListExtractor<R extends InfoItem> extends Extractor {
 
     public ListExtractor(StreamingService service, String url) {
         super(service, url);
     }
 
+    /**
+     * A {@link InfoItemsPage InfoItemsPage} corresponding to the initial page where the items are from the initial request and
+     * the nextPageUrl relative to it.
+     *
+     * @return a {@link InfoItemsPage} corresponding to the initial page
+     */
     @Nonnull
-    public abstract InfoItemsCollector<? extends InfoItem, ?> getInfoItems() throws IOException, ExtractionException;
+    public abstract InfoItemsPage<R> getInitialPage() throws IOException, ExtractionException;
+
+    /**
+     * Returns an url that can be used to get the next page relative to the initial one.<br/>
+     * <p>Usually, these links will only work in the implementation itself.</p>
+     *
+     * @return an url pointing to the next page relative to the initial page
+     * @see #getPage(String)
+     */
     public abstract String getNextPageUrl() throws IOException, ExtractionException;
-    public abstract InfoItemPage<? extends InfoItem> getPage(final String nextPageUrl) throws IOException, ExtractionException;
+
+    /**
+     * Get a list of items corresponding to the specific requested page.
+     *
+     * @param nextPageUrl any next page url got from the exclusive implementation of the list extractor
+     * @return a {@link InfoItemsPage} corresponding to the requested page
+     * @see #getNextPageUrl()
+     * @see InfoItemsPage#getNextPageUrl()
+     */
+    public abstract InfoItemsPage<R> getPage(final String nextPageUrl) throws IOException, ExtractionException;
 
     public boolean hasNextPage() throws IOException, ExtractionException {
         final String nextPageUrl = getNextPageUrl();
@@ -29,14 +53,34 @@ public abstract class ListExtractor extends Extractor {
     // Inner
     //////////////////////////////////////////////////////////////////////////*/
 
-    public static class InfoItemPage<T extends InfoItem> {
+    /**
+     * A class that is used to wrap a list of gathered items and eventual errors, it
+     * also contains a field that points to the next available page ({@link #nextPageUrl}).
+     */
+    public static class InfoItemsPage<T extends InfoItem> {
+        private static final InfoItemsPage<InfoItem> EMPTY =
+                new InfoItemsPage<>(Collections.<InfoItem>emptyList(), "", Collections.<Throwable>emptyList());
+
         /**
-         * The current list of items to this result
+         * A convenient method that returns a representation of an empty page.
+         *
+         * @return a type-safe page with the list of items and errors empty and the nextPageUrl set to an empty string.
+         */
+        public static <T extends InfoItem> InfoItemsPage<T> emptyPage() {
+            //noinspection unchecked
+            return (InfoItemsPage<T>) EMPTY;
+        }
+
+
+        /**
+         * The current list of items of this page
          */
         private final List<T> itemsList;
 
         /**
-         * Next url to fetch more items
+         * Url pointing to the next page relative to this one
+         *
+         * @see ListExtractor#getPage(String)
          */
         private final String nextPageUrl;
 
@@ -45,11 +89,11 @@ public abstract class ListExtractor extends Extractor {
          */
         private final List<Throwable> errors;
 
-        public InfoItemPage(InfoItemsCollector<T, ?> collector, String nextPageUrl) {
+        public InfoItemsPage(InfoItemsCollector<T, ?> collector, String nextPageUrl) {
             this(collector.getItems(), nextPageUrl, collector.getErrors());
         }
 
-        public InfoItemPage(List<T> itemsList, String nextPageUrl, List<Throwable> errors) {
+        public InfoItemsPage(List<T> itemsList, String nextPageUrl, List<Throwable> errors) {
             this.itemsList = itemsList;
             this.nextPageUrl = nextPageUrl;
             this.errors = errors;
@@ -59,7 +103,7 @@ public abstract class ListExtractor extends Extractor {
             return nextPageUrl != null && !nextPageUrl.isEmpty();
         }
 
-        public List<T> getItemsList() {
+        public List<T> getItems() {
             return itemsList;
         }
 

src/main/java/org/schabi/newpipe/extractor/channel/ChannelExtractor.java

@@ -1,16 +1,12 @@
 package org.schabi.newpipe.extractor.channel;
 
-import edu.umd.cs.findbugs.annotations.NonNull;
 import org.schabi.newpipe.extractor.ListExtractor;
 import org.schabi.newpipe.extractor.StreamingService;
 import org.schabi.newpipe.extractor.UrlIdHandler;
-import org.schabi.newpipe.extractor.exceptions.ExtractionException;
 import org.schabi.newpipe.extractor.exceptions.ParsingException;
 import org.schabi.newpipe.extractor.stream.StreamInfoItem;
-import org.schabi.newpipe.extractor.stream.StreamInfoItemsCollector;
 
 import javax.annotation.Nonnull;
-import java.io.IOException;
 
 /*
  * Created by Christian Schabesberger on 25.07.16.
@@ -32,7 +28,7 @@ import java.io.IOException;
  * along with NewPipe.  If not, see <http://www.gnu.org/licenses/>.
  */
 
-public abstract class ChannelExtractor extends ListExtractor {
+public abstract class ChannelExtractor extends ListExtractor<StreamInfoItem> {
 
     public ChannelExtractor(StreamingService service, String url) {
         super(service, url);
@@ -44,12 +40,6 @@ public abstract class ChannelExtractor extends ListExtractor {
         return getService().getChannelUrlIdHandler();
     }
 
-    @NonNull
-    @Override
-    public abstract StreamInfoItemsCollector getInfoItems() throws IOException, ExtractionException;
-    @Override
-    public abstract InfoItemPage<StreamInfoItem> getPage(String nextPageUrl) throws IOException, ExtractionException;
-
     public abstract String getAvatarUrl() throws ParsingException;
     public abstract String getBannerUrl() throws ParsingException;
     public abstract String getFeedUrl() throws ParsingException;

src/main/java/org/schabi/newpipe/extractor/channel/ChannelInfo.java

@@ -1,6 +1,6 @@
 package org.schabi.newpipe.extractor.channel;
 
-import org.schabi.newpipe.extractor.ListExtractor.InfoItemPage;
+import org.schabi.newpipe.extractor.ListExtractor.InfoItemsPage;
 import org.schabi.newpipe.extractor.ListInfo;
 import org.schabi.newpipe.extractor.NewPipe;
 import org.schabi.newpipe.extractor.StreamingService;
@@ -30,18 +30,12 @@ import java.io.IOException;
  * along with NewPipe.  If not, see <http://www.gnu.org/licenses/>.
  */
 
-public class ChannelInfo extends ListInfo {
+public class ChannelInfo extends ListInfo<StreamInfoItem> {
 
     public ChannelInfo(int serviceId, String url, String id, String name) {
         super(serviceId, id, url, name);
     }
 
-
-    public static InfoItemPage<StreamInfoItem> getMoreItems(StreamingService service, String url, String pageUrl)
-            throws IOException, ExtractionException {
-        return service.getChannelExtractor(url).getPage(pageUrl);
-    }
-
     public static ChannelInfo getInfo(String url) throws IOException, ExtractionException {
         return getInfo(NewPipe.getServiceByUrl(url), url);
     }
@@ -52,6 +46,10 @@ public class ChannelInfo extends ListInfo {
         return getInfo(extractor);
     }
 
+    public static InfoItemsPage<StreamInfoItem> getMoreItems(StreamingService service, String url, String pageUrl) throws IOException, ExtractionException {
+        return service.getChannelExtractor(url).getPage(pageUrl);
+    }
+
     public static ChannelInfo getInfo(ChannelExtractor extractor) throws IOException, ExtractionException {
 
         // important data
@@ -79,7 +77,9 @@ public class ChannelInfo extends ListInfo {
             info.addError(e);
         }
 
-        info.setRelatedItems(ExtractorHelper.getInfoItemsOrLogError(info, extractor));
+        final InfoItemsPage<StreamInfoItem> itemsPage = ExtractorHelper.getItemsPageOrLogError(info, extractor);
+        info.setRelatedItems(itemsPage.getItems());
+        info.setNextPageUrl(itemsPage.getNextPageUrl());
 
         try {
             info.setSubscriberCount(extractor.getSubscriberCount());
@@ -92,7 +92,6 @@ public class ChannelInfo extends ListInfo {
             info.addError(e);
         }
 
-        info.setNextPageUrl(extractor.getNextPageUrl());
         return info;
     }
 

src/main/java/org/schabi/newpipe/extractor/kiosk/KioskExtractor.java

@@ -20,18 +20,15 @@ package org.schabi.newpipe.extractor.kiosk;
  * along with NewPipe.  If not, see <http://www.gnu.org/licenses/>.
  */
 
-import edu.umd.cs.findbugs.annotations.NonNull;
 import org.schabi.newpipe.extractor.ListExtractor;
 import org.schabi.newpipe.extractor.StreamingService;
 import org.schabi.newpipe.extractor.exceptions.ExtractionException;
 import org.schabi.newpipe.extractor.exceptions.ParsingException;
 import org.schabi.newpipe.extractor.stream.StreamInfoItem;
-import org.schabi.newpipe.extractor.stream.StreamInfoItemsCollector;
 
 import javax.annotation.Nonnull;
-import java.io.IOException;
 
-public abstract class KioskExtractor extends ListExtractor {
+public abstract class KioskExtractor extends ListExtractor<StreamInfoItem> {
     private String contentCountry = null;
     private final String id;
 
@@ -43,12 +40,6 @@ public abstract class KioskExtractor extends ListExtractor {
         this.id = kioskId;
     }
 
-    @NonNull
-    @Override
-    public abstract StreamInfoItemsCollector getInfoItems() throws IOException, ExtractionException;
-    @Override
-    public abstract InfoItemPage<StreamInfoItem> getPage(String nextPageUrl) throws IOException, ExtractionException;
-
     /**
      * For certain Websites the content of a kiosk will be different depending
      * on the country you want to poen the website in. Therefore you should

src/main/java/org/schabi/newpipe/extractor/kiosk/KioskInfo.java

@@ -30,16 +30,16 @@ import org.schabi.newpipe.extractor.utils.ExtractorHelper;
 
 import java.io.IOException;
 
-public class KioskInfo extends ListInfo {
+public class KioskInfo extends ListInfo<StreamInfoItem> {
 
     private KioskInfo(int serviceId, String id, String url, String name) {
         super(serviceId, id, url, name);
     }
 
-    public static ListExtractor.InfoItemPage<StreamInfoItem> getMoreItems(StreamingService service,
+    public static ListExtractor.InfoItemsPage<StreamInfoItem> getMoreItems(StreamingService service,
-                                                                          String url,
+                                                                           String url,
-                                                                          String pageUrl,
+                                                                           String pageUrl,
-                                                                          String contentCountry) throws IOException, ExtractionException {
+                                                                           String contentCountry) throws IOException, ExtractionException {
         KioskList kl = service.getKioskList();
         KioskExtractor extractor = kl.getExtractorByUrl(url, pageUrl);
         extractor.setContentCountry(contentCountry);
@@ -75,7 +75,9 @@ public class KioskInfo extends ListInfo {
 
         KioskInfo info = new KioskInfo(serviceId, id, name, url);
 
-        info.setRelatedItems(ExtractorHelper.getInfoItemsOrLogError(info, extractor));
+        final ListExtractor.InfoItemsPage<StreamInfoItem> itemsPage = ExtractorHelper.getItemsPageOrLogError(info, extractor);
+        info.setRelatedItems(itemsPage.getItems());
+        info.setNextPageUrl(itemsPage.getNextPageUrl());
 
         return info;
     }

src/main/java/org/schabi/newpipe/extractor/playlist/PlaylistExtractor.java

@@ -1,18 +1,14 @@
 package org.schabi.newpipe.extractor.playlist;
 
-import edu.umd.cs.findbugs.annotations.NonNull;
 import org.schabi.newpipe.extractor.ListExtractor;
 import org.schabi.newpipe.extractor.StreamingService;
 import org.schabi.newpipe.extractor.UrlIdHandler;
-import org.schabi.newpipe.extractor.exceptions.ExtractionException;
 import org.schabi.newpipe.extractor.exceptions.ParsingException;
 import org.schabi.newpipe.extractor.stream.StreamInfoItem;
-import org.schabi.newpipe.extractor.stream.StreamInfoItemsCollector;
 
 import javax.annotation.Nonnull;
-import java.io.IOException;
 
-public abstract class PlaylistExtractor extends ListExtractor {
+public abstract class PlaylistExtractor extends ListExtractor<StreamInfoItem> {
 
     public PlaylistExtractor(StreamingService service, String url) {
         super(service, url);
@@ -24,12 +20,6 @@ public abstract class PlaylistExtractor extends ListExtractor {
         return getService().getPlaylistUrlIdHandler();
     }
 
-    @NonNull
-    @Override
-    public abstract StreamInfoItemsCollector getInfoItems() throws IOException, ExtractionException;
-    @Override
-    public abstract InfoItemPage<StreamInfoItem> getPage(String nextPageUrl) throws IOException, ExtractionException;
-
     public abstract String getThumbnailUrl() throws ParsingException;
     public abstract String getBannerUrl() throws ParsingException;
 

src/main/java/org/schabi/newpipe/extractor/playlist/PlaylistInfo.java

@@ -1,26 +1,21 @@
 package org.schabi.newpipe.extractor.playlist;
 
-import org.schabi.newpipe.extractor.ListExtractor.InfoItemPage;
+import org.schabi.newpipe.extractor.ListExtractor.InfoItemsPage;
 import org.schabi.newpipe.extractor.ListInfo;
 import org.schabi.newpipe.extractor.NewPipe;
 import org.schabi.newpipe.extractor.StreamingService;
 import org.schabi.newpipe.extractor.exceptions.ExtractionException;
 import org.schabi.newpipe.extractor.stream.StreamInfoItem;
+import org.schabi.newpipe.extractor.utils.ExtractorHelper;
 
 import java.io.IOException;
 
-import static org.schabi.newpipe.extractor.utils.ExtractorHelper.getInfoItemsOrLogError;
+public class PlaylistInfo extends ListInfo<StreamInfoItem> {
-
-public class PlaylistInfo extends ListInfo {
 
     public PlaylistInfo(int serviceId, String id, String url, String name) {
         super(serviceId, id, url, name);
     }
 
-    public static InfoItemPage<StreamInfoItem> getMoreItems(StreamingService service, String url, String pageUrl) throws IOException, ExtractionException {
-        return service.getPlaylistExtractor(url).getPage(pageUrl);
-    }
-
     public static PlaylistInfo getInfo(String url) throws IOException, ExtractionException {
         return getInfo(NewPipe.getServiceByUrl(url), url);
     }
@@ -31,6 +26,10 @@ public class PlaylistInfo extends ListInfo {
         return getInfo(extractor);
     }
 
+    public static InfoItemsPage<StreamInfoItem> getMoreItems(StreamingService service, String url, String pageUrl) throws IOException, ExtractionException {
+        return service.getPlaylistExtractor(url).getPage(pageUrl);
+    }
+
     /**
      * Get PlaylistInfo from PlaylistExtractor
      *
@@ -75,8 +74,10 @@ public class PlaylistInfo extends ListInfo {
             info.addError(e);
         }
 
-        info.setRelatedItems(getInfoItemsOrLogError(info, extractor));
+        final InfoItemsPage<StreamInfoItem> itemsPage = ExtractorHelper.getItemsPageOrLogError(info, extractor);
-        info.setNextPageUrl(extractor.getNextPageUrl());
+        info.setRelatedItems(itemsPage.getItems());
+        info.setNextPageUrl(itemsPage.getNextPageUrl());
+
         return info;
     }
 

src/main/java/org/schabi/newpipe/extractor/services/soundcloud/SoundcloudChannelExtractor.java

@@ -92,11 +92,11 @@ public class SoundcloudChannelExtractor extends ChannelExtractor {
 
     @Nonnull
     @Override
-    public StreamInfoItemsCollector getInfoItems() throws ExtractionException {
+    public InfoItemsPage<StreamInfoItem> getInitialPage() throws ExtractionException {
         if(streamInfoItemsCollector == null) {
             computeNextPageAndGetStreams();
         }
-        return streamInfoItemsCollector;
+        return new InfoItemsPage<>(streamInfoItemsCollector, getNextPageUrl());
     }
 
     @Override
@@ -123,7 +123,7 @@ public class SoundcloudChannelExtractor extends ChannelExtractor {
     }
 
     @Override
-    public InfoItemPage<StreamInfoItem> getPage(final String pageUrl) throws IOException, ExtractionException {
+    public InfoItemsPage<StreamInfoItem> getPage(final String pageUrl) throws IOException, ExtractionException {
         if (pageUrl == null || pageUrl.isEmpty()) {
             throw new ExtractionException(new IllegalArgumentException("Page url is empty or null"));
         }
@@ -131,6 +131,6 @@ public class SoundcloudChannelExtractor extends ChannelExtractor {
         StreamInfoItemsCollector collector = new StreamInfoItemsCollector(getServiceId());
         String nextPageUrl = SoundcloudParsingHelper.getStreamsFromApiMinItems(15, collector, pageUrl);
 
-        return new InfoItemPage<>(collector, nextPageUrl);
+        return new InfoItemsPage<>(collector, nextPageUrl);
     }
 }

src/main/java/org/schabi/newpipe/extractor/services/soundcloud/SoundcloudChartsExtractor.java

@@ -42,7 +42,7 @@ public class SoundcloudChartsExtractor extends KioskExtractor {
     }
 
     @Override
-    public InfoItemPage<StreamInfoItem> getPage(String pageUrl) throws IOException, ExtractionException {
+    public InfoItemsPage<StreamInfoItem> getPage(String pageUrl) throws IOException, ExtractionException {
         if (pageUrl == null || pageUrl.isEmpty()) {
             throw new ExtractionException(new IllegalArgumentException("Page url is empty or null"));
         }
@@ -50,7 +50,7 @@ public class SoundcloudChartsExtractor extends KioskExtractor {
         StreamInfoItemsCollector collector = new StreamInfoItemsCollector(getServiceId());
         String nextPageUrl = SoundcloudParsingHelper.getStreamsFromApi(collector, pageUrl, true);
 
-        return new InfoItemPage<>(collector, nextPageUrl);
+        return new InfoItemsPage<>(collector, nextPageUrl);
     }
 
 
@@ -86,10 +86,10 @@ public class SoundcloudChartsExtractor extends KioskExtractor {
 
     @Nonnull
     @Override
-    public StreamInfoItemsCollector getInfoItems() throws IOException, ExtractionException {
+    public InfoItemsPage<StreamInfoItem> getInitialPage() throws IOException, ExtractionException {
         if(collector == null) {
             computNextPageAndStreams();
         }
-        return collector;
+        return new InfoItemsPage<>(collector, getNextPageUrl());
     }
 }

src/main/java/org/schabi/newpipe/extractor/services/soundcloud/SoundcloudPlaylistExtractor.java

@@ -70,7 +70,7 @@ public class SoundcloudPlaylistExtractor extends PlaylistExtractor {
             // If the thumbnail is null, traverse the items list and get a valid one,
             // if it also fails, return null
             try {
-                final StreamInfoItemsCollector infoItems = getInfoItems();
+                final InfoItemsPage<StreamInfoItem> infoItems = getInitialPage();
                 if (infoItems.getItems().isEmpty()) return null;
 
                 for (StreamInfoItem item : infoItems.getItems()) {
@@ -113,11 +113,11 @@ public class SoundcloudPlaylistExtractor extends PlaylistExtractor {
 
     @Nonnull
     @Override
-    public StreamInfoItemsCollector getInfoItems() throws IOException, ExtractionException {
+    public InfoItemsPage<StreamInfoItem> getInitialPage() throws IOException, ExtractionException {
-        if(streamInfoItemsCollector == null) {
+        if (streamInfoItemsCollector == null) {
             computeStreamsAndNextPageUrl();
         }
-        return streamInfoItemsCollector;
+        return new InfoItemsPage<>(streamInfoItemsCollector, getNextPageUrl());
     }
 
     private void computeStreamsAndNextPageUrl() throws ExtractionException, IOException {
@@ -134,14 +134,14 @@ public class SoundcloudPlaylistExtractor extends PlaylistExtractor {
 
     @Override
     public String getNextPageUrl() throws IOException, ExtractionException {
-        if(nextPageUrl == null) {
+        if (nextPageUrl == null) {
             computeStreamsAndNextPageUrl();
         }
         return nextPageUrl;
     }
 
     @Override
-    public InfoItemPage<StreamInfoItem> getPage(String pageUrl) throws IOException, ExtractionException {
+    public InfoItemsPage<StreamInfoItem> getPage(String pageUrl) throws IOException, ExtractionException {
         if (pageUrl == null || pageUrl.isEmpty()) {
             throw new ExtractionException(new IllegalArgumentException("Page url is empty or null"));
         }
@@ -149,6 +149,6 @@ public class SoundcloudPlaylistExtractor extends PlaylistExtractor {
         StreamInfoItemsCollector collector = new StreamInfoItemsCollector(getServiceId());
         String nextPageUrl = SoundcloudParsingHelper.getStreamsFromApiMinItems(15, collector, pageUrl);
 
-        return new InfoItemPage<>(collector, nextPageUrl);
+        return new InfoItemsPage<>(collector, nextPageUrl);
     }
 }

src/main/java/org/schabi/newpipe/extractor/services/youtube/YoutubeChannelExtractor.java

@@ -150,15 +150,15 @@ public class YoutubeChannelExtractor extends ChannelExtractor {
 
     @Nonnull
     @Override
-    public StreamInfoItemsCollector getInfoItems() throws ExtractionException {
+    public InfoItemsPage<StreamInfoItem> getInitialPage() throws ExtractionException {
         StreamInfoItemsCollector collector = new StreamInfoItemsCollector(getServiceId());
         Element ul = doc.select("ul[id=\"browse-items-primary\"]").first();
         collectStreamsFrom(collector, ul);
-        return collector;
+        return new InfoItemsPage<>(collector, getNextPageUrl());
     }
 
     @Override
-    public InfoItemPage<StreamInfoItem> getPage(String pageUrl) throws IOException, ExtractionException {
+    public InfoItemsPage<StreamInfoItem> getPage(String pageUrl) throws IOException, ExtractionException {
         if (pageUrl == null || pageUrl.isEmpty()) {
             throw new ExtractionException(new IllegalArgumentException("Page url is empty or null"));
         }
@@ -178,7 +178,7 @@ public class YoutubeChannelExtractor extends ChannelExtractor {
         final Document ajaxHtml = Jsoup.parse(ajaxJson.getString("content_html"), pageUrl);
         collectStreamsFrom(collector, ajaxHtml.select("body").first());
 
-        return new InfoItemPage<>(collector, getNextPageUrlFromAjaxPage(ajaxJson, pageUrl));
+        return new InfoItemsPage<>(collector, getNextPageUrlFromAjaxPage(ajaxJson, pageUrl));
     }
 
     private String getNextPageUrlFromAjaxPage(final JsonObject ajaxJson, final String pageUrl)

src/main/java/org/schabi/newpipe/extractor/services/youtube/YoutubePlaylistExtractor.java

@@ -129,15 +129,15 @@ public class YoutubePlaylistExtractor extends PlaylistExtractor {
 
     @Nonnull
     @Override
-    public StreamInfoItemsCollector getInfoItems() throws IOException, ExtractionException {
+    public InfoItemsPage<StreamInfoItem> getInitialPage() throws IOException, ExtractionException {
         StreamInfoItemsCollector collector = new StreamInfoItemsCollector(getServiceId());
         Element tbody = doc.select("tbody[id=\"pl-load-more-destination\"]").first();
         collectStreamsFrom(collector, tbody);
-        return collector;
+        return new InfoItemsPage<>(collector, getNextPageUrl());
     }
 
     @Override
-    public InfoItemPage<StreamInfoItem> getPage(final String pageUrl) throws IOException, ExtractionException {
+    public InfoItemsPage<StreamInfoItem> getPage(final String pageUrl) throws IOException, ExtractionException {
         if (pageUrl == null || pageUrl.isEmpty()) {
             throw new ExtractionException(new IllegalArgumentException("Page url is empty or null"));
         }
@@ -156,7 +156,7 @@ public class YoutubePlaylistExtractor extends PlaylistExtractor {
 
         collectStreamsFrom(collector, pageHtml.select("tbody[id=\"pl-load-more-destination\"]").first());
 
-        return new InfoItemPage<>(collector, getNextPageUrlFromAjax(pageJson, pageUrl));
+        return new InfoItemsPage<>(collector, getNextPageUrlFromAjax(pageJson, pageUrl));
     }
 
     private String getNextPageUrlFromAjax(final JsonObject pageJson, final String pageUrl)

src/main/java/org/schabi/newpipe/extractor/services/youtube/YoutubeTrendingExtractor.java

@@ -25,7 +25,6 @@ import org.jsoup.nodes.Document;
 import org.jsoup.nodes.Element;
 import org.jsoup.select.Elements;
 import org.schabi.newpipe.extractor.Downloader;
-import org.schabi.newpipe.extractor.ListExtractor;
 import org.schabi.newpipe.extractor.StreamingService;
 import org.schabi.newpipe.extractor.UrlIdHandler;
 import org.schabi.newpipe.extractor.exceptions.ExtractionException;
@@ -70,7 +69,7 @@ public class YoutubeTrendingExtractor extends KioskExtractor {
     }
 
     @Override
-    public ListExtractor.InfoItemPage<StreamInfoItem> getPage(String pageUrl) {
+    public InfoItemsPage<StreamInfoItem> getPage(String pageUrl) {
         return null;
     }
 
@@ -89,7 +88,7 @@ public class YoutubeTrendingExtractor extends KioskExtractor {
 
     @Nonnull
     @Override
-    public StreamInfoItemsCollector getInfoItems() throws ParsingException {
+    public InfoItemsPage<StreamInfoItem> getInitialPage() throws ParsingException {
         StreamInfoItemsCollector collector = new StreamInfoItemsCollector(getServiceId());
         Elements uls = doc.select("ul[class*=\"expanded-shelf-content-list\"]");
         for(Element ul : uls) {
@@ -165,6 +164,6 @@ public class YoutubeTrendingExtractor extends KioskExtractor {
             }
         }
 
-        return collector;
+        return new InfoItemsPage<>(collector, getNextPageUrl());
     }
 }

src/main/java/org/schabi/newpipe/extractor/utils/ExtractorHelper.java

@@ -4,9 +4,9 @@ import org.schabi.newpipe.extractor.Info;
 import org.schabi.newpipe.extractor.InfoItem;
 import org.schabi.newpipe.extractor.InfoItemsCollector;
 import org.schabi.newpipe.extractor.ListExtractor;
+import org.schabi.newpipe.extractor.ListExtractor.InfoItemsPage;
 import org.schabi.newpipe.extractor.stream.StreamExtractor;
 import org.schabi.newpipe.extractor.stream.StreamInfo;
-import org.schabi.newpipe.extractor.stream.StreamInfoItemsCollector;
 
 import java.util.Collections;
 import java.util.List;
@@ -14,40 +14,29 @@ import java.util.List;
 public class ExtractorHelper {
     private ExtractorHelper() {}
 
-    public static List<InfoItem> getInfoItemsOrLogError(Info info, ListExtractor extractor) {
+    public static <T extends InfoItem> InfoItemsPage<T> getItemsPageOrLogError(Info info, ListExtractor<T> extractor) {
-        InfoItemsCollector collector;
         try {
-            collector = extractor.getInfoItems();
+            InfoItemsPage<T> page = extractor.getInitialPage();
+            info.addAllErrors(page.getErrors());
+
+            return page;
         } catch (Exception e) {
             info.addError(e);
-            return Collections.emptyList();
+            return InfoItemsPage.emptyPage();
         }
-        // Get from collector
-        return getInfoItems(info, collector);
     }
 
 
     public static List<InfoItem> getRelatedVideosOrLogError(StreamInfo info, StreamExtractor extractor) {
-        StreamInfoItemsCollector collector;
         try {
-            collector = extractor.getRelatedVideos();
+            InfoItemsCollector<? extends InfoItem, ?> collector = extractor.getRelatedVideos();
-        } catch (Exception e) {
-            info.addError(e);
-            return Collections.emptyList();
-        }
-        // Get from collector
-        return getInfoItems(info, collector);
-    }
-
-    private static List<InfoItem> getInfoItems(Info info, InfoItemsCollector collector) {
-        List<InfoItem> result;
-        try {
-            result = collector.getItems();
             info.addAllErrors(collector.getErrors());
+
+            //noinspection unchecked
+            return (List<InfoItem>) collector.getItems();
         } catch (Exception e) {
             info.addError(e);
             return Collections.emptyList();
         }
-        return result;
     }
 }

src/test/java/org/schabi/newpipe/extractor/services/DefaultTests.java

@@ -1,7 +1,6 @@
 package org.schabi.newpipe.extractor.services;
 
 import org.schabi.newpipe.extractor.InfoItem;
-import org.schabi.newpipe.extractor.InfoItemsCollector;
 import org.schabi.newpipe.extractor.ListExtractor;
 import org.schabi.newpipe.extractor.stream.StreamInfoItem;
 
@@ -32,28 +31,30 @@ public final class DefaultTests {
         }
     }
 
-    public static void defaultTestRelatedItems(ListExtractor extractor, int expectedServiceId) throws Exception {
+    public static <T extends InfoItem> ListExtractor.InfoItemsPage<T> defaultTestRelatedItems(ListExtractor<T> extractor, int expectedServiceId) throws Exception {
-        final InfoItemsCollector<? extends InfoItem, ?> itemsCollector = extractor.getInfoItems();
+        final ListExtractor.InfoItemsPage<T> page = extractor.getInitialPage();
-        final List<? extends InfoItem> itemsList = itemsCollector.getItems();
+        final List<T> itemsList = page.getItems();
-        List<Throwable> errors = itemsCollector.getErrors();
+        List<Throwable> errors = page.getErrors();
 
         defaultTestListOfItems(expectedServiceId, itemsList, errors);
+        return page;
     }
 
-    public static ListExtractor.InfoItemPage<? extends InfoItem> defaultTestMoreItems(ListExtractor extractor, int expectedServiceId) throws Exception {
+    public static <T extends InfoItem> ListExtractor.InfoItemsPage<T> defaultTestMoreItems(ListExtractor<T> extractor, int expectedServiceId) throws Exception {
         assertTrue("Doesn't have more items", extractor.hasNextPage());
-        ListExtractor.InfoItemPage<? extends InfoItem> nextPage = extractor.getPage(extractor.getNextPageUrl());
+        ListExtractor.InfoItemsPage<T> nextPage = extractor.getPage(extractor.getNextPageUrl());
-        assertTrue("Next page is empty", !nextPage.getItemsList().isEmpty());
+        final List<T> items = nextPage.getItems();
+        assertTrue("Next page is empty", !items.isEmpty());
         assertEmptyErrors("Next page have errors", nextPage.getErrors());
 
-        defaultTestListOfItems(expectedServiceId, nextPage.getItemsList(), nextPage.getErrors());
+        defaultTestListOfItems(expectedServiceId, nextPage.getItems(), nextPage.getErrors());
         return nextPage;
     }
 
-    public static void defaultTestGetPageInNewExtractor(ListExtractor extractor, ListExtractor newExtractor, int expectedServiceId) throws Exception {
+    public static void defaultTestGetPageInNewExtractor(ListExtractor<? extends InfoItem> extractor, ListExtractor<? extends InfoItem> newExtractor, int expectedServiceId) throws Exception {
         final String nextPageUrl = extractor.getNextPageUrl();
 
-        final ListExtractor.InfoItemPage<? extends InfoItem> page = newExtractor.getPage(nextPageUrl);
+        final ListExtractor.InfoItemsPage<? extends InfoItem> page = newExtractor.getPage(nextPageUrl);
-        defaultTestListOfItems(expectedServiceId, page.getItemsList(), page.getErrors());
+        defaultTestListOfItems(expectedServiceId, page.getItems(), page.getErrors());
     }
 }

src/test/java/org/schabi/newpipe/extractor/services/soundcloud/SoundcloudChartsExtractorTest.java

@@ -4,9 +4,10 @@ import org.junit.BeforeClass;
 import org.junit.Ignore;
 import org.junit.Test;
 import org.schabi.newpipe.Downloader;
-import org.schabi.newpipe.extractor.InfoItemsCollector;
+import org.schabi.newpipe.extractor.ListExtractor;
 import org.schabi.newpipe.extractor.NewPipe;
 import org.schabi.newpipe.extractor.kiosk.KioskExtractor;
+import org.schabi.newpipe.extractor.stream.StreamInfoItem;
 
 import java.util.List;
 
@@ -47,29 +48,29 @@ public class SoundcloudChartsExtractorTest {
 
     @Test
     public void testGetStreams() throws Exception {
-        InfoItemsCollector collector = extractor.getInfoItems();
+        ListExtractor.InfoItemsPage<StreamInfoItem> page = extractor.getInitialPage();
-        if(!collector.getErrors().isEmpty()) {
+        if(!page.getErrors().isEmpty()) {
             System.err.println("----------");
-            List<Throwable> errors = collector.getErrors();
+            List<Throwable> errors = page.getErrors();
             for(Throwable e: errors) {
                 e.printStackTrace();
                 System.err.println("----------");
             }
         }
         assertTrue("no streams are received",
-                !collector.getItems().isEmpty()
+                !page.getItems().isEmpty()
-                        && collector.getErrors().isEmpty());
+                        && page.getErrors().isEmpty());
     }
 
     @Test
     public void testGetStreamsErrors() throws Exception {
-        assertTrue("errors during stream list extraction", extractor.getInfoItems().getErrors().isEmpty());
+        assertTrue("errors during stream list extraction", extractor.getInitialPage().getErrors().isEmpty());
     }
 
     @Test
     public void testHasMoreStreams() throws Exception {
         // Setup the streams
-        extractor.getInfoItems();
+        extractor.getInitialPage();
         assertTrue("has more streams", extractor.hasNextPage());
     }
 
@@ -80,9 +81,9 @@ public class SoundcloudChartsExtractorTest {
 
     @Test
     public void testGetNextPage() throws Exception {
-        extractor.getInfoItems().getItems();
+        extractor.getInitialPage().getItems();
         assertFalse("extractor has next streams", extractor.getPage(extractor.getNextPageUrl()) == null
-                || extractor.getPage(extractor.getNextPageUrl()).getItemsList().isEmpty());
+                || extractor.getPage(extractor.getNextPageUrl()).getItems().isEmpty());
     }
 
     @Test

src/test/java/org/schabi/newpipe/extractor/services/soundcloud/SoundcloudPlaylistExtractorTest.java

@@ -6,12 +6,12 @@ import org.junit.Test;
 import org.junit.experimental.runners.Enclosed;
 import org.junit.runner.RunWith;
 import org.schabi.newpipe.Downloader;
-import org.schabi.newpipe.extractor.InfoItem;
 import org.schabi.newpipe.extractor.ListExtractor;
 import org.schabi.newpipe.extractor.NewPipe;
 import org.schabi.newpipe.extractor.ServiceList;
 import org.schabi.newpipe.extractor.playlist.PlaylistExtractor;
 import org.schabi.newpipe.extractor.services.BasePlaylistExtractorTest;
+import org.schabi.newpipe.extractor.stream.StreamInfoItem;
 
 import static org.junit.Assert.*;
 import static org.schabi.newpipe.extractor.ExtractorAsserts.assertIsSecureUrl;
@@ -274,11 +274,11 @@ public class SoundcloudPlaylistExtractorTest {
 
         @Test
         public void testMoreRelatedItems() throws Exception {
-            ListExtractor.InfoItemPage<? extends InfoItem> currentPage = defaultTestMoreItems(extractor, ServiceList.SoundCloud.getServiceId());
+            ListExtractor.InfoItemsPage<StreamInfoItem> currentPage = defaultTestMoreItems(extractor, ServiceList.SoundCloud.getServiceId());
             // Test for 2 more levels
             for (int i = 0; i < 2; i++) {
                 currentPage = extractor.getPage(currentPage.getNextPageUrl());
-                defaultTestListOfItems(SoundCloud.getServiceId(), currentPage.getItemsList(), currentPage.getErrors());
+                defaultTestListOfItems(SoundCloud.getServiceId(), currentPage.getItems(), currentPage.getErrors());
             }
         }
 

src/test/java/org/schabi/newpipe/extractor/services/youtube/YoutubePlaylistExtractorTest.java

@@ -5,12 +5,12 @@ import org.junit.Test;
 import org.junit.experimental.runners.Enclosed;
 import org.junit.runner.RunWith;
 import org.schabi.newpipe.Downloader;
-import org.schabi.newpipe.extractor.InfoItem;
 import org.schabi.newpipe.extractor.ListExtractor;
 import org.schabi.newpipe.extractor.NewPipe;
 import org.schabi.newpipe.extractor.ServiceList;
 import org.schabi.newpipe.extractor.playlist.PlaylistExtractor;
 import org.schabi.newpipe.extractor.services.BasePlaylistExtractorTest;
+import org.schabi.newpipe.extractor.stream.StreamInfoItem;
 
 import static org.junit.Assert.assertEquals;
 import static org.junit.Assert.assertTrue;
@@ -181,11 +181,11 @@ public class YoutubePlaylistExtractorTest {
 
         @Test
         public void testMoreRelatedItems() throws Exception {
-            ListExtractor.InfoItemPage<? extends InfoItem> currentPage = defaultTestMoreItems(extractor, ServiceList.YouTube.getServiceId());
+            ListExtractor.InfoItemsPage<StreamInfoItem> currentPage = defaultTestMoreItems(extractor, ServiceList.YouTube.getServiceId());
             // Test for 2 more levels
             for (int i = 0; i < 2; i++) {
                 currentPage = extractor.getPage(currentPage.getNextPageUrl());
-                defaultTestListOfItems(YouTube.getServiceId(), currentPage.getItemsList(), currentPage.getErrors());
+                defaultTestListOfItems(YouTube.getServiceId(), currentPage.getItems(), currentPage.getErrors());
             }
         }
 

src/test/java/org/schabi/newpipe/extractor/services/youtube/YoutubeTrendingExtractorTest.java

@@ -23,8 +23,9 @@ package org.schabi.newpipe.extractor.services.youtube;
 import org.junit.BeforeClass;
 import org.junit.Test;
 import org.schabi.newpipe.Downloader;
-import org.schabi.newpipe.extractor.InfoItemsCollector;
+import org.schabi.newpipe.extractor.ListExtractor;
 import org.schabi.newpipe.extractor.NewPipe;
+import org.schabi.newpipe.extractor.stream.StreamInfoItem;
 import org.schabi.newpipe.extractor.utils.Utils;
 
 import static junit.framework.TestCase.assertFalse;
@@ -66,27 +67,27 @@ public class YoutubeTrendingExtractorTest {
 
     @Test
     public void testGetStreamsQuantity() throws Exception {
-        InfoItemsCollector collector = extractor.getInfoItems();
+        ListExtractor.InfoItemsPage<StreamInfoItem> page = extractor.getInitialPage();
-        Utils.printErrors(collector.getErrors());
+        Utils.printErrors(page.getErrors());
-        assertTrue("no streams are received", collector.getItems().size() >= 20);
+        assertTrue("no streams are received", page.getItems().size() >= 20);
     }
 
     @Test
     public void testGetStreamsErrors() throws Exception {
-        assertEmptyErrors("errors during stream list extraction", extractor.getInfoItems().getErrors());
+        assertEmptyErrors("errors during stream list extraction", extractor.getInitialPage().getErrors());
     }
 
     @Test
     public void testHasMoreStreams() throws Exception {
         // Setup the streams
-        extractor.getInfoItems();
+        extractor.getInitialPage();
         assertFalse("has more streams", extractor.hasNextPage());
     }
 
     @Test
     public void testGetNextPage() {
         assertTrue("extractor has next streams", extractor.getPage(extractor.getNextPageUrl()) == null
-                || extractor.getPage(extractor.getNextPageUrl()).getItemsList().isEmpty());
+                || extractor.getPage(extractor.getNextPageUrl()).getItems().isEmpty());
     }
 
     @Test