Show an empty view when there is no widget available

Test: Remove all widgets from work profile using TestDpc. Observe
      empty view is shown in the full widget tray. Add back some
      widgets to work profile and observe widgets showing up in the
      full widgets tray

Bug: 179797520
Change-Id: I2e1fcb5a0014568a4674e2bcc0a3ed3c6ec5a44a

res/layout/widgets_full_sheet.xml

@@ -15,6 +15,7 @@
 -->
 <com.android.launcher3.widget.picker.WidgetsFullSheet
     xmlns:android="http://schemas.android.com/apk/res/android"
+    xmlns:tools="http://schemas.android.com/tools"
     android:layout_width="match_parent"
     android:layout_height="match_parent"
     android:orientation="vertical"
@@ -27,6 +28,14 @@
         android:background="?android:attr/colorPrimary"
         android:elevation="4dp">
 
+        <TextView
+            android:id="@+id/no_widgets_text"
+            android:layout_width="match_parent"
+            android:layout_height="match_parent"
+            android:gravity="center"
+            android:visibility="gone"
+            tools:text="No widgets available" />
+
         <!-- Fast scroller popup -->
         <TextView
             android:id="@+id/fast_scroller_popup"

res/values/strings.xml

@@ -74,6 +74,9 @@
     <!-- Search bar text shown in the popup view showing all available widgets installed on the
          device. [CHAR_LIMIT=50] -->
     <string name="widgets_full_sheet_search_bar_hint">Search</string>
+    <!-- Text shown when there is no widgets shown in the popup view showing all available widgets
+         installed on the device. [CHAR_LIMIT=none] -->
+    <string name="no_widgets_available">No widgets available</string>
 
     <!-- All Apps -->
     <!-- Search bar text in the apps view. [CHAR_LIMIT=50] -->

src/com/android/launcher3/widget/picker/WidgetsFullSheet.java

@@ -82,6 +82,7 @@ public class WidgetsFullSheet extends BaseWidgetSheet
     @Nullable private PersonalWorkPagedView mViewPager;
     private int mInitialTabsHeight = 0;
     private View mTabsView;
+    private TextView mNoWidgetsView;
     private SearchAndRecommendationViewHolder mSearchAndRecommendationViewHolder;
     private SearchAndRecommendationsScrollController mSearchAndRecommendationsScrollController;
 
@@ -141,19 +142,32 @@ public class WidgetsFullSheet extends BaseWidgetSheet
                 mViewPager);
         fastScroller.setOnFastScrollChangeListener(mSearchAndRecommendationsScrollController);
 
+        mNoWidgetsView = findViewById(R.id.no_widgets_text);
+
         onWidgetsBound();
     }
 
     @Override
     public void onActivePageChanged(int currentActivePage) {
-        WidgetsRecyclerView currentRecyclerView =
-                mAdapters.get(currentActivePage).mWidgetsRecyclerView;
+        AdapterHolder currentAdapterHolder = mAdapters.get(currentActivePage);
+        WidgetsRecyclerView currentRecyclerView = currentAdapterHolder.mWidgetsRecyclerView;
         currentRecyclerView.bindFastScrollbar();
         mSearchAndRecommendationsScrollController.setCurrentRecyclerView(currentRecyclerView);
 
+        updateNoWidgetsView(currentAdapterHolder);
+
         reset();
     }
 
+    private void updateNoWidgetsView(AdapterHolder adapterHolder) {
+        boolean isWidgetAvailable = adapterHolder.mWidgetsListAdapter.getItemCount() > 0;
+        adapterHolder.mWidgetsRecyclerView.setVisibility(isWidgetAvailable ? VISIBLE : GONE);
+
+        // Always resets the text in case this is updated by search.
+        mNoWidgetsView.setText(R.string.no_widgets_available);
+        mNoWidgetsView.setVisibility(isWidgetAvailable ? GONE : VISIBLE);
+    }
+
     private void reset() {
         mAdapters.get(AdapterHolder.PRIMARY).mWidgetsRecyclerView.scrollToTop();
         if (mHasWorkProfile) {
@@ -276,6 +290,8 @@ public class WidgetsFullSheet extends BaseWidgetSheet
         AdapterHolder primaryUserAdapterHolder = mAdapters.get(AdapterHolder.PRIMARY);
         primaryUserAdapterHolder.setup(findViewById(R.id.primary_widgets_list_view));
         primaryUserAdapterHolder.mWidgetsListAdapter.setWidgets(allWidgets);
+        updateNoWidgetsView(primaryUserAdapterHolder);
+
         if (mHasWorkProfile) {
             AdapterHolder workUserAdapterHolder = mAdapters.get(AdapterHolder.WORK);
             workUserAdapterHolder.setup(findViewById(R.id.work_widgets_list_view));