[Feed] Move scroll logic to Mediator

Bug: 863171
Change-Id: Ibf9c93098fef18bbda60370d6bdd771442debd9f
Reviewed-on: https://chromium-review.googlesource.com/1145788Reviewed-by: Theresa <twellington@chromium.org>
Commit-Queue: Becky Zhou <huayinz@chromium.org>
Cr-Commit-Position: refs/heads/master@{#577209}

chrome/android/feed/core/java/src/org/chromium/chrome/browser/feed/FeedNewTabPage.java

@@ -15,7 +15,6 @@ import android.widget.FrameLayout;
 
 import com.google.android.libraries.feed.api.scope.FeedProcessScope;
 import com.google.android.libraries.feed.api.scope.FeedStreamScope;
-import com.google.android.libraries.feed.api.stream.ScrollListener;
 import com.google.android.libraries.feed.api.stream.Stream;
 import com.google.android.libraries.feed.host.stream.CardConfiguration;
 import com.google.android.libraries.feed.host.stream.SnackbarApi;
@@ -45,13 +44,10 @@ import java.util.Arrays;
 /**
  * Provides a new tab page that displays an interest feed rendered list of content suggestions.
  */
-public class FeedNewTabPage
-        extends NewTabPage implements TouchEnabledDelegate, NewTabPageLayout.ScrollDelegate {
+public class FeedNewTabPage extends NewTabPage implements TouchEnabledDelegate {
     private final FeedNewTabPageMediator mMediator;
     private final StreamLifecycleManager mStreamLifecycleManager;
     private final Stream mStream;
-    private final ScrollListener mStreamScrollListener;
-    private final SnapScrollHelper mSnapScrollHelper;
 
     private FrameLayout mRootView;
     private SectionHeaderView mSectionHeaderView;
@@ -152,44 +148,14 @@ public class FeedNewTabPage
 
         mStream = streamScope.getStream();
         mStreamLifecycleManager = new StreamLifecycleManager(mStream, activity, tab);
-        mSnapScrollHelper =
-                new SnapScrollHelper(mNewTabPageManager, mNewTabPageLayout, mStream.getView());
-        mSectionHeaderView = (SectionHeaderView) LayoutInflater.from(activity).inflate(
-                R.layout.new_tab_page_snippets_expandable_header, null);
-        mMediator = new FeedNewTabPageMediator(this);
-
-        mStream.getView().setBackgroundColor(Color.WHITE);
-        mRootView.addView(mStream.getView());
-
-        mStream.setHeaderViews(Arrays.asList(mNewTabPageLayout, mSectionHeaderView));
-
-        // Listen for layout changes on the NewTabPageView itself to catch changes in scroll
-        // position that are due to layout changes after e.g. device rotation. This contrasts with
-        // regular scrolling, which is observed through an OnScrollListener.
-        mRootView.addOnLayoutChangeListener(
-                (v, left, top, right, bottom, oldLeft, oldTop, oldRight, oldBottom) -> {
-                    mSnapScrollHelper.handleScroll();
-                });
 
-        mStreamScrollListener = new ScrollListener() {
-            @Override
-            public void onScrollStateChanged(int state) {}
-
-            @Override
-            public void onScrolled(int dx, int dy) {
-                mSnapScrollHelper.handleScroll();
-            }
-        };
-        mStream.addScrollListener(mStreamScrollListener);
-    }
+        LayoutInflater inflater = LayoutInflater.from(activity);
+        mNewTabPageLayout = (NewTabPageLayout) inflater.inflate(R.layout.new_tab_page_layout, null);
+        mSectionHeaderView = (SectionHeaderView) inflater.inflate(
+                R.layout.new_tab_page_snippets_expandable_header, null);
 
-    @Override
-    protected void initializeMainView(Context context) {
-        int topPadding = context.getResources().getDimensionPixelOffset(R.dimen.tab_strip_height);
-        mRootView = new FrameLayout(context);
-        mRootView.setLayoutParams(new FrameLayout.LayoutParams(
-                FrameLayout.LayoutParams.MATCH_PARENT, FrameLayout.LayoutParams.MATCH_PARENT));
-        mRootView.setPadding(0, topPadding, 0, 0);
+        mMediator = new FeedNewTabPageMediator(this,
+                new SnapScrollHelper(mNewTabPageManager, mNewTabPageLayout, mStream.getView()));
 
         // Don't store a direct reference to the activity, because it might change later if the tab
         // is reparented.
@@ -200,19 +166,30 @@ public class FeedNewTabPage
                         this::setTouchEnabled, closeContextMenuCallback);
         mTab.getWindowAndroid().addContextMenuCloseListener(contextMenuManager);
 
-        LayoutInflater inflater = LayoutInflater.from(context);
-        mNewTabPageLayout = (NewTabPageLayout) inflater.inflate(R.layout.new_tab_page_layout, null);
         mNewTabPageLayout.initialize(mNewTabPageManager, mTab, mTileGroupDelegate,
                 mSearchProviderHasLogo,
-                TemplateUrlService.getInstance().isDefaultSearchEngineGoogle(), this,
+                TemplateUrlService.getInstance().isDefaultSearchEngineGoogle(), mMediator,
                 contextMenuManager, new UiConfig(mRootView));
+
+        mStream.getView().setBackgroundColor(Color.WHITE);
+        mRootView.addView(mStream.getView());
+
+        mStream.setHeaderViews(Arrays.asList(mNewTabPageLayout, mSectionHeaderView));
+    }
+
+    @Override
+    protected void initializeMainView(Context context) {
+        int topPadding = context.getResources().getDimensionPixelOffset(R.dimen.tab_strip_height);
+        mRootView = new FrameLayout(context);
+        mRootView.setLayoutParams(new FrameLayout.LayoutParams(
+                FrameLayout.LayoutParams.MATCH_PARENT, FrameLayout.LayoutParams.MATCH_PARENT));
+        mRootView.setPadding(0, topPadding, 0, 0);
     }
 
     @Override
     public void destroy() {
         super.destroy();
         mMediator.destroy();
-        mStream.removeScrollListener(mStreamScrollListener);
         mImageLoader.destroy();
         mStreamLifecycleManager.destroy();
     }
@@ -261,40 +238,4 @@ public class FeedNewTabPage
     public void setTouchEnabled(boolean enabled) {
         // TODO(twellington): implement this method.
     }
-
-    // ScrollDelegate interface.
-
-    @Override
-    public boolean isScrollViewInitialized() {
-        // During startup the view may not be fully initialized, so we check to see if some basic
-        // view properties (height of the RecyclerView) are sane.
-        return mStream != null && mStream.getView().getHeight() > 0;
-    }
-
-    @Override
-    public int getVerticalScrollOffset() {
-        // This method returns a valid vertical scroll offset only when the first header view in the
-        // Stream is visible. In all other cases, this returns 0.
-        if (!isScrollViewInitialized()) return 0;
-
-        int firstChildTop = mStream.getChildTopAt(0);
-        return firstChildTop != Stream.POSITION_NOT_KNOWN ? -firstChildTop : 0;
-    }
-
-    @Override
-    public boolean isChildVisibleAtPosition(int position) {
-        return isScrollViewInitialized() && mStream.isChildAtPositionVisible(position);
-    }
-
-    @Override
-    public void snapScroll() {
-        if (!isScrollViewInitialized()) return;
-
-        int initialScroll = getVerticalScrollOffset();
-        int scrollTo = mSnapScrollHelper.calculateSnapPosition(initialScroll);
-
-        // Calculating the snap position should be idempotent.
-        assert scrollTo == mSnapScrollHelper.calculateSnapPosition(scrollTo);
-        mStream.smoothScrollBy(0, scrollTo - initialScroll);
-    }
 }

chrome/android/feed/core/java/src/org/chromium/chrome/browser/feed/FeedNewTabPageMediator.java

@@ -6,7 +6,12 @@ package org.chromium.chrome.browser.feed;
 
 import android.content.res.Resources;
 
+import com.google.android.libraries.feed.api.stream.ScrollListener;
+import com.google.android.libraries.feed.api.stream.Stream;
+
 import org.chromium.chrome.R;
+import org.chromium.chrome.browser.ntp.NewTabPageLayout;
+import org.chromium.chrome.browser.ntp.SnapScrollHelper;
 import org.chromium.chrome.browser.ntp.snippets.SectionHeader;
 import org.chromium.chrome.browser.preferences.Pref;
 import org.chromium.chrome.browser.preferences.PrefChangeRegistrar;
@@ -16,17 +21,20 @@ import org.chromium.chrome.browser.preferences.PrefServiceBridge;
  * A mediator for the {@link FeedNewTabPage} responsible for interacting with the
  * native library and handling business logic.
  */
-class FeedNewTabPageMediator {
+class FeedNewTabPageMediator implements NewTabPageLayout.ScrollDelegate {
     private final FeedNewTabPage mCoordinator;
+    private final SnapScrollHelper mSnapScrollHelper;
     private final PrefChangeRegistrar mPrefChangeRegistrar;
 
+    private ScrollListener mStreamScrollListener;
     private SectionHeader mSectionHeader;
 
     /**
      * @param feedNewTabPage The {@link FeedNewTabPage} that interacts with this class.
      */
-    FeedNewTabPageMediator(FeedNewTabPage feedNewTabPage) {
+    FeedNewTabPageMediator(FeedNewTabPage feedNewTabPage, SnapScrollHelper snapScrollHelper) {
         mCoordinator = feedNewTabPage;
+        mSnapScrollHelper = snapScrollHelper;
         initializeProperties();
 
         mPrefChangeRegistrar = new PrefChangeRegistrar();
@@ -36,6 +44,7 @@ class FeedNewTabPageMediator {
 
     /** Clears any dependencies. */
     void destroy() {
+        mCoordinator.getStream().removeScrollListener(mStreamScrollListener);
         mPrefChangeRegistrar.destroy();
     }
 
@@ -44,6 +53,25 @@ class FeedNewTabPageMediator {
      * TODO(huayinz): Introduce a Model for these properties.
      */
     private void initializeProperties() {
+        // Listen for layout changes on the NewTabPageView itself to catch changes in scroll
+        // position that are due to layout changes after e.g. device rotation. This contrasts with
+        // regular scrolling, which is observed through an OnScrollListener.
+        mCoordinator.getView().addOnLayoutChangeListener(
+                (v, left, top, right, bottom, oldLeft, oldTop, oldRight, oldBottom) -> {
+                    mSnapScrollHelper.handleScroll();
+                });
+
+        mStreamScrollListener = new ScrollListener() {
+            @Override
+            public void onScrollStateChanged(int state) {}
+
+            @Override
+            public void onScrolled(int dx, int dy) {
+                mSnapScrollHelper.handleScroll();
+            }
+        };
+        mCoordinator.getStream().addScrollListener(mStreamScrollListener);
+
         Resources res = mCoordinator.getSectionHeaderView().getResources();
         mSectionHeader =
                 new SectionHeader(res.getString(R.string.ntp_article_suggestions_section_header),
@@ -72,4 +100,42 @@ class FeedNewTabPageMediator {
         // TODO(huayinz): Update the section header view through a ModelChangeProcessor.
         mCoordinator.getSectionHeaderView().updateIconDrawable();
     }
+
+    // ScrollDelegate interface.
+
+    @Override
+    public boolean isScrollViewInitialized() {
+        Stream stream = mCoordinator.getStream();
+        // During startup the view may not be fully initialized, so we check to see if some basic
+        // view properties (height of the RecyclerView) are sane.
+        return stream != null && stream.getView().getHeight() > 0;
+    }
+
+    @Override
+    public int getVerticalScrollOffset() {
+        // This method returns a valid vertical scroll offset only when the first header view in the
+        // Stream is visible. In all other cases, this returns 0.
+        if (!isScrollViewInitialized()) return 0;
+
+        int firstChildTop = mCoordinator.getStream().getChildTopAt(0);
+        return firstChildTop != Stream.POSITION_NOT_KNOWN ? -firstChildTop : 0;
+    }
+
+    @Override
+    public boolean isChildVisibleAtPosition(int position) {
+        return isScrollViewInitialized()
+                && mCoordinator.getStream().isChildAtPositionVisible(position);
+    }
+
+    @Override
+    public void snapScroll() {
+        if (!isScrollViewInitialized()) return;
+
+        int initialScroll = getVerticalScrollOffset();
+        int scrollTo = mSnapScrollHelper.calculateSnapPosition(initialScroll);
+
+        // Calculating the snap position should be idempotent.
+        assert scrollTo == mSnapScrollHelper.calculateSnapPosition(scrollTo);
+        mCoordinator.getStream().smoothScrollBy(0, scrollTo - initialScroll);
+    }
 }