[TabSelectionEditor] Shows with preselected Tab

This CL adds an API to TabSelectionEditorController that shows the
TabSelectionEditor with the given tabs, and the first n tabs being
selected. There is also a divider shows between the first n selected
tabs and the rest of the tabs.

Change-Id: I32aa764dc62bbabc89fe54641963b9f64274134e
Bug: 1004570
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1896866Reviewed-by: Wei-Yin Chen (陳威尹) <wychen@chromium.org>
Reviewed-by: Yusuf Ozuysal <yusufo@chromium.org>
Commit-Queue: Mei Liang <meiliang@chromium.org>
Cr-Commit-Position: refs/heads/master@{#713897}

chrome/android/features/tab_ui/java/src/org/chromium/chrome/browser/tasks/tab_management/TabListCoordinator.java

@@ -129,6 +129,13 @@ public class TabListCoordinator implements Destroyable {
             }, TabGridViewBinder::bindClosableTab);
 
             recyclerListener = (holder) -> {
+                int holderItemViewType = holder.getItemViewType();
+
+                if (holderItemViewType != UiType.CLOSABLE
+                        && holderItemViewType != UiType.SELECTABLE) {
+                    return;
+                }
+
                 ViewLookupCachingFrameLayout root = (ViewLookupCachingFrameLayout) holder.itemView;
                 ImageView thumbnail = (ImageView) root.fastFindViewById(R.id.tab_thumbnail);
                 if (thumbnail == null) return;
@@ -305,4 +312,13 @@ public class TabListCoordinator implements Destroyable {
             PropertyModelChangeProcessor.ViewBinder<PropertyModel, T, PropertyKey> binder) {
         mAdapter.registerType(typeId, builder, binder);
     }
+
+    /**
+     * Inserts a special {@link org.chromium.ui.modelutil.MVCListAdapter.ListItem} at given index of
+     * the model list.
+     * @see TabListMediator#addSpecialItemToModel(int, int, PropertyModel).
+     */
+    void addSpecialListItem(int index, @UiType int uiType, PropertyModel model) {
+        mMediator.addSpecialItemToModel(index, uiType, model);
+    }
 }

chrome/android/features/tab_ui/java/src/org/chromium/chrome/browser/tasks/tab_management/TabListMediator.java

@@ -1155,4 +1155,17 @@ class TabListMediator {
     void setTabRestoreCompletedForTesting(boolean isRestored) {
         mTabRestoreCompleted = isRestored;
     }
+
+    /**
+     * Inserts a special {@link org.chromium.ui.modelutil.MVCListAdapter.ListItem} at given index of
+     * the current {@link TabListModel}.
+     *
+     * @param index The index of the {@link org.chromium.ui.modelutil.MVCListAdapter.ListItem} to be
+     *              inserted.
+     * @param uiType The view type the model will bind to.
+     * @param model The model that will be bound to a view.
+     */
+    void addSpecialItemToModel(int index, @UiType int uiType, PropertyModel model) {
+        mModel.add(index, new SimpleRecyclerViewAdapter.ListItem(uiType, model));
+    }
 }

chrome/android/features/tab_ui/java/src/org/chromium/chrome/browser/tasks/tab_management/TabProperties.java

@@ -23,13 +23,14 @@ import java.lang.annotation.RetentionPolicy;
  */
 public class TabProperties {
     /** IDs for possible types of UI in the tab list. */
-    @IntDef({UiType.SELECTABLE, UiType.CLOSABLE, UiType.STRIP, UiType.MESSAGE})
+    @IntDef({UiType.SELECTABLE, UiType.CLOSABLE, UiType.STRIP, UiType.MESSAGE, UiType.DIVIDER})
     @Retention(RetentionPolicy.SOURCE)
     public @interface UiType {
         int SELECTABLE = 0;
         int CLOSABLE = 1;
         int STRIP = 2;
         int MESSAGE = 3;
+        int DIVIDER = 4;
     }
 
     public static final PropertyModel.WritableIntPropertyKey TAB_ID =

chrome/android/features/tab_ui/java/src/org/chromium/chrome/browser/tasks/tab_management/TabSelectionEditorCoordinator.java

@@ -5,6 +5,8 @@
 package org.chromium.chrome.browser.tasks.tab_management;
 
 import android.content.Context;
+import android.support.v7.widget.GridLayoutManager;
+import android.support.v7.widget.RecyclerView;
 import android.view.LayoutInflater;
 import android.view.View;
 
@@ -37,6 +39,14 @@ class TabSelectionEditorCoordinator {
          */
         void show(List<Tab> tabs);
 
+        /**
+         * Shows the TabSelectionEditor with the given {@Link Tab}s, and the first
+         * {@code preSelectedTabCount} tabs being selected.
+         * @param tabs List of {@link Tab}s to show.
+         * @param preSelectedTabCount Number of selected {@link Tab}s.
+         */
+        void show(List<Tab> tabs, int preSelectedTabCount);
+
         /**
          * Hides the TabSelectionEditor.
          */
@@ -79,10 +89,32 @@ class TabSelectionEditorCoordinator {
         mContext = context;
         mParentView = parentView;
         mTabModelSelector = tabModelSelector;
+
         mTabListCoordinator = new TabListCoordinator(TabListCoordinator.TabListMode.GRID, context,
                 mTabModelSelector, tabContentManager::getTabThumbnailWithCallback, null, false,
                 null, null, null, TabProperties.UiType.SELECTABLE, this::getSelectionDelegate, null,
                 null, false, COMPONENT_NAME);
+        mTabListCoordinator.registerItemType(TabProperties.UiType.DIVIDER, () -> {
+            return LayoutInflater.from(context).inflate(R.layout.divider_preference, null, false);
+        }, (model, view, propertyKey) -> {});
+        RecyclerView.LayoutManager layoutManager =
+                mTabListCoordinator.getContainerView().getLayoutManager();
+        if (layoutManager instanceof GridLayoutManager) {
+            ((GridLayoutManager) layoutManager)
+                    .setSpanSizeLookup(new GridLayoutManager.SpanSizeLookup() {
+                        @Override
+                        public int getSpanSize(int i) {
+                            int itemType = mTabListCoordinator.getContainerView()
+                                                   .getAdapter()
+                                                   .getItemViewType(i);
+
+                            if (itemType == TabProperties.UiType.DIVIDER) {
+                                return ((GridLayoutManager) layoutManager).getSpanCount();
+                            }
+                            return 1;
+                        }
+                    });
+        }
 
         mTabSelectionEditorLayout = LayoutInflater.from(context)
                 .inflate(R.layout.tab_selection_editor_layout, null)
@@ -108,9 +140,16 @@ class TabSelectionEditorCoordinator {
     /**
      * Resets {@link TabListCoordinator} with the provided list.
      * @param tabs List of {@link Tab}s to reset.
+     * @param preSelectedCount First {@code preSelectedCount} {@code tabs} are pre-selected.
      */
-    void resetWithListOfTabs(@Nullable List<Tab> tabs) {
+    void resetWithListOfTabs(@Nullable List<Tab> tabs, int preSelectedCount) {
         mTabListCoordinator.resetWithListOfTabs(tabs);
+
+        if (tabs != null && preSelectedCount > 0) {
+            assert preSelectedCount < tabs.size();
+            mTabListCoordinator.addSpecialListItem(
+                    preSelectedCount, TabProperties.UiType.DIVIDER, new PropertyModel());
+        }
     }
 
     /**

chrome/android/features/tab_ui/java/src/org/chromium/chrome/browser/tasks/tab_management/TabSelectionEditorMediator.java

@@ -29,7 +29,9 @@ import org.chromium.chrome.tab_ui.R;
 import org.chromium.ui.modelutil.PropertyModel;
 
 import java.util.ArrayList;
+import java.util.HashSet;
 import java.util.List;
+import java.util.Set;
 
 /**
  * This class is the mediator that contains all business logic for TabSelectionEditor component. It
@@ -45,8 +47,9 @@ class TabSelectionEditorMediator
         /**
          * Handles the reset event.
          * @param tabs List of {@link Tab}s to reset.
+         * @param preSelectedCount First {@code preSelectedCount} {@code tabs} are pre-selected.
          */
-        void resetWithListOfTabs(@Nullable List<Tab> tabs);
+        void resetWithListOfTabs(@Nullable List<Tab> tabs, int preSelectedCount);
     }
 
     /**
@@ -181,8 +184,27 @@ class TabSelectionEditorMediator
      */
     @Override
     public void show(List<Tab> tabs) {
-        mResetHandler.resetWithListOfTabs(tabs);
+        show(tabs, 0);
+    }
+
+    @Override
+    public void show(List<Tab> tabs, int preSelectedTabCount) {
         mSelectionDelegate.setSelectionModeEnabledForZeroItems(true);
+
+        if (preSelectedTabCount > 0) {
+            assert preSelectedTabCount <= tabs.size();
+
+            Set<Integer> preSelectedTabIds = new HashSet<>();
+
+            for (int i = 0; i < preSelectedTabCount; i++) {
+                preSelectedTabIds.add(tabs.get(i).getId());
+            }
+
+            mSelectionDelegate.setSelectedItems(preSelectedTabIds);
+        }
+
+        mResetHandler.resetWithListOfTabs(tabs, preSelectedTabCount);
+
         if (mPositionProvider != null) {
             mModel.set(TabSelectionEditorProperties.SELECTION_EDITOR_POSITION_RECT,
                     mPositionProvider.getSelectionEditorPositionRect());
@@ -221,7 +243,7 @@ class TabSelectionEditorMediator
 
     @Override
     public void hide() {
-        mResetHandler.resetWithListOfTabs(null);
+        mResetHandler.resetWithListOfTabs(null, 0);
         mModel.set(TabSelectionEditorProperties.IS_VISIBLE, false);
     }
 

chrome/android/features/tab_ui/javatests/src/org/chromium/chrome/browser/tasks/tab_management/RecyclerViewMatcherUtils.java

@@ -10,6 +10,7 @@ import android.view.View;
 
 import org.hamcrest.Description;
 import org.hamcrest.Matcher;
+import org.hamcrest.TypeSafeMatcher;
 
 /**
  * Contains useful RecyclerViewMatcher.
@@ -66,4 +67,75 @@ public class RecyclerViewMatcherUtils {
             }
         };
     }
+
+    /**
+     * This matcher matches RecyclerView that has a ViewHolder that matches the given view holder
+     * matcher at the given adapter position.
+     *
+     * @param position The adapter position.
+     * @param viewHolderMatcher A view holder to match.
+     * @return A matcher that matches view at adapter position and matches the given viewHolder
+     *         matcher.
+     */
+    public static Matcher<View> atPositionWithViewHolder(
+            int position, Matcher<RecyclerView.ViewHolder> viewHolderMatcher) {
+        return new BoundedMatcher<View, RecyclerView>(RecyclerView.class) {
+            @Override
+            protected boolean matchesSafely(RecyclerView recyclerView) {
+                recyclerView.scrollToPosition(position);
+                RecyclerView.ViewHolder viewHolder =
+                        recyclerView.findViewHolderForAdapterPosition(position);
+
+                if (viewHolder == null) return false;
+
+                return viewHolderMatcher.matches(viewHolder);
+            }
+
+            @Override
+            public void describeTo(Description description) {
+                description.appendText(viewHolderMatcher + " at position " + position);
+            }
+        };
+    }
+
+    /**
+     * This matcher matches the ViewHolder that has an adapter position equals to the given
+     * position.
+     *
+     * @param position The position to match.
+     * @return A matcher that matches the viewHolder at the given position.
+     */
+    public static Matcher<RecyclerView.ViewHolder> withViewHolderAtPosition(int position) {
+        return new TypeSafeMatcher<RecyclerView.ViewHolder>() {
+            @Override
+            protected boolean matchesSafely(RecyclerView.ViewHolder viewHolder) {
+                return viewHolder.getAdapterPosition() == position;
+            }
+
+            @Override
+            public void describeTo(Description description) {
+                description.appendText("ViewHolder with adapter position: " + position);
+            }
+        };
+    }
+
+    /**
+     * This matcher matches a ViewHolder that has the given item type.
+     *
+     * @param itemType The item type to match.
+     * @return A matcher that matches a ViewHolder with the given item type.
+     */
+    public static Matcher<RecyclerView.ViewHolder> withItemType(int itemType) {
+        return new TypeSafeMatcher<RecyclerView.ViewHolder>() {
+            @Override
+            protected boolean matchesSafely(RecyclerView.ViewHolder viewHolder) {
+                return viewHolder.getItemViewType() == itemType;
+            }
+
+            @Override
+            public void describeTo(Description description) {
+                description.appendText("ViewHolder with item type: " + itemType);
+            }
+        };
+    }
 }

chrome/android/features/tab_ui/javatests/src/org/chromium/chrome/browser/tasks/tab_management/TabSelectionEditorTest.java

@@ -5,6 +5,7 @@
 package org.chromium.chrome.browser.tasks.tab_management;
 
 import android.os.Build;
+import android.support.test.InstrumentationRegistry;
 import android.support.test.filters.MediumTest;
 
 import org.junit.Before;
@@ -24,6 +25,7 @@ import org.chromium.chrome.browser.tabmodel.TabModelSelector;
 import org.chromium.chrome.tab_ui.R;
 import org.chromium.chrome.test.ChromeJUnit4ClassRunner;
 import org.chromium.chrome.test.ChromeTabbedActivityTestRule;
+import org.chromium.chrome.test.util.ChromeTabUtils;
 import org.chromium.chrome.test.util.browser.Features;
 import org.chromium.content_public.browser.test.util.TestThreadUtils;
 import org.chromium.ui.test.util.UiRestriction;
@@ -183,6 +185,58 @@ public class TabSelectionEditorTest {
         mRobot.resultRobot.verifyToolbarActionButtonDisabled();
     }
 
+    @Test
+    @MediumTest
+    public void testShowTabsWithPreSelectedTabs() {
+        List<Tab> tabs = getTabsInCurrentTabModel();
+        int preSelectedTabCount = 1;
+        TestThreadUtils.runOnUiThreadBlocking(
+                () -> { mTabSelectionEditorController.show(tabs, preSelectedTabCount); });
+
+        mRobot.resultRobot.verifyTabSelectionEditorIsVisible()
+                .verifyToolbarActionButtonDisabled()
+                .verifyToolbarActionButtonWithResourceId(R.string.tab_selection_editor_group)
+                .verifyToolbarSelectionText("1 selected")
+                .verifyHasAtLeastNItemVisible(tabs.size() + 1)
+                .verifyItemSelectedAtAdapterPosition(0)
+                .verifyHasItemViewTypeAtAdapterPosition(1, TabProperties.UiType.DIVIDER)
+                .verifyDividerAlwaysStartsAtTheEdgeOfScreen();
+    }
+
+    @Test
+    @MediumTest
+    public void testShowTabsWithPreSelectedTabs_10Tabs() {
+        int preSelectedTabCount = 10;
+        int additionalTabCount =
+                preSelectedTabCount + 1 - mTabModelSelector.getCurrentModel().getCount();
+
+        for (int i = 0; i < additionalTabCount; i++) {
+            ChromeTabUtils.newTabFromMenu(InstrumentationRegistry.getInstrumentation(),
+                    mActivityTestRule.getActivity(), mTabModelSelector.isIncognitoSelected(), true);
+        }
+
+        List<Tab> tabs = getTabsInCurrentTabModel();
+
+        TestThreadUtils.runOnUiThreadBlocking(
+                () -> { mTabSelectionEditorController.show(tabs, preSelectedTabCount); });
+
+        mRobot.resultRobot.verifyToolbarSelectionText("10 selected")
+                .verifyHasItemViewTypeAtAdapterPosition(
+                        preSelectedTabCount, TabProperties.UiType.DIVIDER)
+                .verifyDividerAlwaysStartsAtTheEdgeOfScreenAtPosition(preSelectedTabCount);
+    }
+
+    @Test
+    @MediumTest
+    public void testDividerIsNotClickable() {
+        List<Tab> tabs = getTabsInCurrentTabModel();
+        int preSelectedTabCount = 1;
+        TestThreadUtils.runOnUiThreadBlocking(
+                () -> { mTabSelectionEditorController.show(tabs, preSelectedTabCount); });
+
+        mRobot.resultRobot.verifyDividerNotClickableNotFocusable();
+    }
+
     private List<Tab> getTabsInCurrentTabModel() {
         List<Tab> tabs = new ArrayList<>();
 

chrome/android/features/tab_ui/javatests/src/org/chromium/chrome/browser/tasks/tab_management/TabSelectionEditorTestingRobot.java

@@ -8,9 +8,12 @@ import static android.support.test.espresso.Espresso.onView;
 import static android.support.test.espresso.action.ViewActions.click;
 import static android.support.test.espresso.assertion.ViewAssertions.matches;
 import static android.support.test.espresso.contrib.RecyclerViewActions.actionOnItemAtPosition;
+import static android.support.test.espresso.contrib.RecyclerViewActions.scrollToPosition;
 import static android.support.test.espresso.matcher.RootMatchers.withDecorView;
+import static android.support.test.espresso.matcher.ViewMatchers.isClickable;
 import static android.support.test.espresso.matcher.ViewMatchers.isDisplayed;
 import static android.support.test.espresso.matcher.ViewMatchers.isEnabled;
+import static android.support.test.espresso.matcher.ViewMatchers.isFocusable;
 import static android.support.test.espresso.matcher.ViewMatchers.withClassName;
 import static android.support.test.espresso.matcher.ViewMatchers.withContentDescription;
 import static android.support.test.espresso.matcher.ViewMatchers.withId;
@@ -21,6 +24,10 @@ import static org.hamcrest.Matchers.allOf;
 import static org.hamcrest.Matchers.is;
 import static org.hamcrest.Matchers.not;
 
+import static org.chromium.chrome.browser.tasks.tab_management.RecyclerViewMatcherUtils.atPosition;
+import static org.chromium.chrome.browser.tasks.tab_management.RecyclerViewMatcherUtils.atPositionWithViewHolder;
+import static org.chromium.chrome.browser.tasks.tab_management.RecyclerViewMatcherUtils.withItemType;
+
 import android.os.Build;
 import android.support.test.espresso.NoMatchingRootException;
 import android.support.test.espresso.Root;
@@ -41,7 +48,7 @@ public class TabSelectionEditorTestingRobot {
     /**
      * @return A root matcher that matches the TabSelectionEditor popup decor view.
      */
-    private static Matcher<Root> isTabSelectionEditorPopup() {
+    public static Matcher<Root> isTabSelectionEditorPopup() {
         return new TypeSafeMatcher<Root>() {
             @Override
             public void describeTo(Description description) {
@@ -66,7 +73,7 @@ public class TabSelectionEditorTestingRobot {
     /**
      * @return A view matcher that matches the item is selected.
      */
-    private static Matcher<View> itemIsSelected() {
+    public static Matcher<View> itemIsSelected() {
         return new BoundedMatcher<View, SelectableTabGridView>(SelectableTabGridView.class) {
             private SelectableTabGridView mSelectableTabGridView;
             @Override
@@ -105,6 +112,23 @@ public class TabSelectionEditorTestingRobot {
         };
     }
 
+    /**
+     * @return A view matcher that matches a divider view.
+     */
+    public static Matcher<View> isDivider() {
+        return new TypeSafeMatcher<View>() {
+            @Override
+            protected boolean matchesSafely(View view) {
+                return view.getId() == org.chromium.chrome.tab_ui.R.id.divider_view;
+            }
+
+            @Override
+            public void describeTo(Description description) {
+                description.appendText("is divider");
+            }
+        };
+    }
+
     public final TabSelectionEditorTestingRobot.Result resultRobot;
     public final TabSelectionEditorTestingRobot.Action actionRobot;
 
@@ -252,5 +276,67 @@ public class TabSelectionEditorTestingRobot {
             onView(withText(text)).check(matches(isDisplayed()));
             return this;
         }
+
+        Result verifyDividerAlwaysStartsAtTheEdgeOfScreen() {
+            onView(allOf(isDivider(),
+                           withParent(withId(org.chromium.chrome.tab_ui.R.id.tab_list_view))))
+                    .inRoot(isTabSelectionEditorPopup())
+                    .check(matches(isDisplayed()))
+                    .check((v, noMatchException) -> {
+                        if (noMatchException != null) throw noMatchException;
+
+                        View parentView = (View) v.getParent();
+                        Assert.assertEquals(parentView.getPaddingStart(), (int) v.getX());
+                    });
+            return this;
+        }
+
+        Result verifyDividerAlwaysStartsAtTheEdgeOfScreenAtPosition(int position) {
+            onView(withId(org.chromium.chrome.tab_ui.R.id.tab_list_view))
+                    .inRoot(isTabSelectionEditorPopup())
+                    .perform(scrollToPosition(position));
+
+            onView(atPosition(position, isDivider()))
+                    .inRoot(isTabSelectionEditorPopup())
+                    .check(matches(isDisplayed()))
+                    .check((v, noMatchException) -> {
+                        if (noMatchException != null) throw noMatchException;
+
+                        View parentView = (View) v.getParent();
+                        Assert.assertEquals(parentView.getPaddingStart(), (int) v.getX());
+                    });
+
+            return this;
+        }
+
+        Result verifyDividerNotClickableNotFocusable() {
+            onView(allOf(isDivider(),
+                           withParent(withId(org.chromium.chrome.tab_ui.R.id.tab_list_view))))
+                    .inRoot(isTabSelectionEditorPopup())
+                    .check(matches(not(isClickable())))
+                    .check(matches(not(isFocusable())));
+            return this;
+        }
+
+        /**
+         * Verifies the TabSelectionEditor has an ItemView at given position that matches the given
+         * targetItemViewType.
+         *
+         * First this method scrolls to the given adapter position to make sure ViewHolder for the
+         * given position is visible.
+         *
+         * @param position Adapter position.
+         * @param targetItemViewType The item view type to be matched.
+         * @return {@link Result} to do chain verification.
+         */
+        Result verifyHasItemViewTypeAtAdapterPosition(int position, int targetItemViewType) {
+            onView(withId(org.chromium.chrome.tab_ui.R.id.tab_list_view))
+                    .inRoot(isTabSelectionEditorPopup())
+                    .perform(scrollToPosition(position));
+            onView(atPositionWithViewHolder(position, withItemType(targetItemViewType)))
+                    .inRoot(isTabSelectionEditorPopup())
+                    .check(matches(isDisplayed()));
+            return this;
+        }
     }
 }

chrome/android/features/tab_ui/junit/src/org/chromium/chrome/browser/tasks/tab_management/TabListMediatorUnitTest.java

@@ -7,9 +7,12 @@ package org.chromium.chrome.browser.tasks.tab_management;
 import static org.hamcrest.CoreMatchers.equalTo;
 import static org.hamcrest.CoreMatchers.instanceOf;
 import static org.hamcrest.CoreMatchers.not;
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertNotEquals;
 import static org.junit.Assert.assertNotNull;
 import static org.junit.Assert.assertNull;
 import static org.junit.Assert.assertThat;
+import static org.junit.Assert.assertTrue;
 import static org.mockito.ArgumentMatchers.any;
 import static org.mockito.ArgumentMatchers.anyBoolean;
 import static org.mockito.ArgumentMatchers.anyInt;
@@ -1355,6 +1358,30 @@ public class TabListMediatorUnitTest {
         verify(mRemoveEditor).apply();
     }
 
+    @Test
+    public void addSpecialItem() {
+        mMediator.addSpecialItemToModel(0, TabProperties.UiType.DIVIDER, new PropertyModel());
+
+        assertTrue(mModel.size() > 0);
+        assertEquals(TabProperties.UiType.DIVIDER, mModel.get(0).type);
+    }
+
+    @Test
+    public void addSpecialItem_notPersistOnReset() {
+        mMediator.addSpecialItemToModel(0, TabProperties.UiType.DIVIDER, new PropertyModel());
+        assertEquals(TabProperties.UiType.DIVIDER, mModel.get(0).type);
+
+        List<Tab> tabs = new ArrayList<>(Arrays.asList(mTab1, mTab2));
+        mMediator.resetWithListOfTabs(tabs, false, false);
+        assertThat(mModel.size(), equalTo(2));
+        assertNotEquals(TabProperties.UiType.DIVIDER, mModel.get(0).type);
+        assertNotEquals(TabProperties.UiType.DIVIDER, mModel.get(1).type);
+
+        mMediator.addSpecialItemToModel(1, TabProperties.UiType.DIVIDER, new PropertyModel());
+        assertThat(mModel.size(), equalTo(3));
+        assertEquals(TabProperties.UiType.DIVIDER, mModel.get(1).type);
+    }
+
     private void initAndAssertAllProperties() {
         List<Tab> tabs = new ArrayList<>();
         for (int i = 0; i < mTabModel.getCount(); i++) {

chrome/android/java/res/layout/divider_preference.xml

@@ -3,7 +3,8 @@
      Use of this source code is governed by a BSD-style license that can be
      found in the LICENSE file. -->
 
-<View 
+<View
     xmlns:android="http://schemas.android.com/apk/res/android"
+    android:id="@+id/divider_view"
     style="@style/HorizontalDivider"
     android:importantForAccessibility="no" />