[StartSurface] Return to home surface when clicking the back button and the...

[StartSurface] Return to home surface when clicking the back button and the explore surface is showing

Bug: 982018
Change-Id: I8d92b1234061869c4fc8c920eb1be8bf2f44db58
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1724659Reviewed-by: Yusuf Ozuysal <yusufo@chromium.org>
Commit-Queue: Ganggui Tang <gogerald@chromium.org>
Auto-Submit: Ganggui Tang <gogerald@chromium.org>
Cr-Commit-Position: refs/heads/master@{#682233}

chrome/android/features/start_surface/internal/java/src/org/chromium/chrome/features/start_surface/BottomBarView.java

@@ -121,4 +121,15 @@ class BottomBarView extends FrameLayout {
     public void setOnClickListener(StartSurfaceProperties.BottomBarClickListener listener) {
         mOnClickListener = listener;
     }
+
+    /**
+     * Select the Tab at the specified position if needed.
+     * @param index The specified position.
+     */
+    public void selectTabAt(int index) {
+        assert index >= 0 && index < mTabLayout.getTabCount();
+
+        if (index == mTabLayout.getSelectedTabPosition()) return;
+        mTabLayout.getTabAt(index).select();
+    }
 }
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chrome/android/features/start_surface/internal/java/src/org/chromium/chrome/features/start_surface/BottomBarViewBinder.java

@@ -5,6 +5,7 @@
 package org.chromium.chrome.features.start_surface;
 
 import static org.chromium.chrome.features.start_surface.StartSurfaceProperties.BOTTOM_BAR_CLICKLISTENER;
+import static org.chromium.chrome.features.start_surface.StartSurfaceProperties.BOTTOM_BAR_SELECTED_TAB_POSITION;
 import static org.chromium.chrome.features.start_surface.StartSurfaceProperties.IS_INCOGNITO;
 import static org.chromium.chrome.features.start_surface.StartSurfaceProperties.IS_SHOWING_OVERVIEW;
 
@@ -14,12 +15,14 @@ import org.chromium.ui.modelutil.PropertyModel;
 /** The view binder of the bottom bar. */
 class BottomBarViewBinder {
     public static void bind(PropertyModel model, BottomBarView view, PropertyKey propertyKey) {
-        if (IS_INCOGNITO == propertyKey) {
+        if (BOTTOM_BAR_CLICKLISTENER == propertyKey) {
+            view.setOnClickListener(model.get(BOTTOM_BAR_CLICKLISTENER));
+        } else if (BOTTOM_BAR_SELECTED_TAB_POSITION == propertyKey) {
+            view.selectTabAt(model.get(BOTTOM_BAR_SELECTED_TAB_POSITION));
+        } else if (IS_INCOGNITO == propertyKey) {
             view.setIncognito(model.get(IS_INCOGNITO));
         } else if (IS_SHOWING_OVERVIEW == propertyKey) {
             view.setVisibility(model.get(IS_SHOWING_OVERVIEW));
-        } else if (BOTTOM_BAR_CLICKLISTENER == propertyKey) {
-            view.setOnClickListener(model.get(BOTTOM_BAR_CLICKLISTENER));
         }
     }
 }
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chrome/android/features/start_surface/internal/java/src/org/chromium/chrome/features/start_surface/StartSurfaceMediator.java

@@ -5,6 +5,7 @@
 package org.chromium.chrome.features.start_surface;
 
 import static org.chromium.chrome.features.start_surface.StartSurfaceProperties.BOTTOM_BAR_CLICKLISTENER;
+import static org.chromium.chrome.features.start_surface.StartSurfaceProperties.BOTTOM_BAR_SELECTED_TAB_POSITION;
 import static org.chromium.chrome.features.start_surface.StartSurfaceProperties.FEED_SURFACE_COORDINATOR;
 import static org.chromium.chrome.features.start_surface.StartSurfaceProperties.IS_EXPLORE_SURFACE_VISIBLE;
 import static org.chromium.chrome.features.start_surface.StartSurfaceProperties.IS_INCOGNITO;
@@ -110,8 +111,10 @@ class StartSurfaceMediator
 
     @Override
     public boolean onBackPressed() {
-        // TODO(crbug.com/982018): Check whether explore surface is shown, if yes, switch back to
-        // home surface.
+        if (mPropertyModel != null && mPropertyModel.get(IS_EXPLORE_SURFACE_VISIBLE)) {
+            setExploreSurfaceVisibility(false);
+            return true;
+        }
         return mGridController.onBackPressed();
     }
 
@@ -159,6 +162,10 @@ class StartSurfaceMediator
         }
 
         mPropertyModel.set(IS_EXPLORE_SURFACE_VISIBLE, isVisible);
+
+        // Update the 'BOTTOM_BAR_SELECTED_TAB_POSITION' property to reflect the change. This is
+        // needed when clicking back button on the explore surface.
+        mPropertyModel.set(BOTTOM_BAR_SELECTED_TAB_POSITION, isVisible ? 1 : 0);
     }
 
     void updateIncognitoMode(boolean isIncognito) {

chrome/android/features/start_surface/internal/java/src/org/chromium/chrome/features/start_surface/StartSurfaceProperties.java

@@ -26,6 +26,8 @@ class StartSurfaceProperties {
             new PropertyModel.WritableObjectPropertyKey<BottomBarClickListener>();
     public static final PropertyModel.WritableIntPropertyKey BOTTOM_BAR_HEIGHT =
             new PropertyModel.WritableIntPropertyKey();
+    public static final PropertyModel.WritableIntPropertyKey BOTTOM_BAR_SELECTED_TAB_POSITION =
+            new PropertyModel.WritableIntPropertyKey();
     public static final PropertyModel.WritableBooleanPropertyKey IS_EXPLORE_SURFACE_VISIBLE =
             new PropertyModel.WritableBooleanPropertyKey();
     public static final PropertyModel.WritableBooleanPropertyKey IS_INCOGNITO =
@@ -38,6 +40,6 @@ class StartSurfaceProperties {
     public static final PropertyModel.WritableIntPropertyKey TOP_BAR_HEIGHT =
             new PropertyModel.WritableIntPropertyKey();
     public static final PropertyKey[] ALL_KEYS = new PropertyKey[] {BOTTOM_BAR_CLICKLISTENER,
-            BOTTOM_BAR_HEIGHT, IS_EXPLORE_SURFACE_VISIBLE, IS_INCOGNITO, IS_SHOWING_OVERVIEW,
-            FEED_SURFACE_COORDINATOR, TOP_BAR_HEIGHT};
+            BOTTOM_BAR_HEIGHT, BOTTOM_BAR_SELECTED_TAB_POSITION, IS_EXPLORE_SURFACE_VISIBLE,
+            IS_INCOGNITO, IS_SHOWING_OVERVIEW, FEED_SURFACE_COORDINATOR, TOP_BAR_HEIGHT};
 }
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