Add a message to empty ContentSuggestions sections

ios/chrome/browser/ui/content_suggestions/content_suggestions_view_controller.mm

 // Copyright 2016 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #import "ios/chrome/browser/ui/content_suggestions/content_suggestions_view_controller.h"
 
 #include "base/mac/foundation_util.h"
 #import "ios/chrome/browser/ui/collection_view/cells/MDCCollectionViewCell+Chrome.h"
 #import "ios/chrome/browser/ui/collection_view/cells/collection_view_item.h"
 #import "ios/chrome/browser/ui/collection_view/collection_view_model.h"
@@ skipping 47 matching lines @@
 - (void)dismissEntryAtIndexPath:(NSIndexPath*)indexPath {
   if (!indexPath || ![self.collectionViewModel hasItemAtIndexPath:indexPath]) {
     return;
   }
 
   [self.collectionView performBatchUpdates:^{
     [self collectionView:self.collectionView
         willDeleteItemsAtIndexPaths:@[ indexPath ]];
 
     [self.collectionView deleteItemsAtIndexPaths:@[ indexPath ]];
+
+    // Check if the section is now empty.
+    [self checkEmptySection:indexPath.section];

[lpromero, 2017/03/23 10:54:37]

Can you update the name of the method, as it does more than checking. For
example -addEmptySectionPlaceholderIfNeeded: or something similar.

[gambard, 2017/03/23 15:25:49]

Done.

   }
       completion:^(BOOL) {
         // The context menu could be displayed for the deleted entry.
         [self.suggestionCommandHandler dismissContextMenu];
       }];
 }
 
 - (void)dismissSection:(NSInteger)section {
   if (section >= [self numberOfSectionsInCollectionView:self.collectionView]) {
     return;
@@ skipping 55 matching lines @@
 - (void)collectionView:(UICollectionView*)collectionView
     didSelectItemAtIndexPath:(NSIndexPath*)indexPath {
   [super collectionView:collectionView didSelectItemAtIndexPath:indexPath];
 
   CollectionViewItem* item =
       [self.collectionViewModel itemAtIndexPath:indexPath];
   switch ([self.collectionUpdater contentSuggestionTypeForItem:item]) {
     case ContentSuggestionTypeArticle:
       [self openArticle:item];
       break;
+    case ContentSuggestionTypeEmpty:
+      break;
   }
 }
 
 #pragma mark - ContentSuggestionsExpandableCellDelegate
 
 - (void)collapseCell:(UICollectionViewCell*)cell {
   [self expand:NO cell:cell];
 }
 
 - (void)expandCell:(UICollectionViewCell*)cell {
@@ skipping 107 matching lines @@
 
   ContentSuggestionsArticleItem* articleItem =
       base::mac::ObjCCastStrict<ContentSuggestionsArticleItem>(touchedItem);
 
   [self.suggestionCommandHandler
       displayContextMenuForArticle:articleItem
                            atPoint:touchLocation
                        atIndexPath:touchedItemIndexPath];
 }
 
+// Checks if the |section| is empty and add an empty element if it is the case.
+// Must be called from inside a performBatchUpdates: block.
+- (void)checkEmptySection:(NSInteger)section {
+  if ([self.collectionViewModel numberOfItemsInSection:section] > 0)
+    return;
+  [self.collectionUpdater addEmptyItemForSection:section];
+  NSIndexPath* emptyItem = [NSIndexPath indexPathForItem:0 inSection:section];

[lpromero, 2017/03/23 10:54:37]

Use the return value of –addEmptyItemForSection: once it returns the indexpath.

[gambard, 2017/03/23 15:25:49]

Done.

+  [self.collectionView insertItemsAtIndexPaths:@[ emptyItem ]];
+}
+
 @end