[NTP Snippets] Pass "no suggestions" message from the backend to the UI

components/ntp_snippets/category_info.h

 // 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.
 
 #ifndef COMPONENTS_NTP_SNIPPETS_CATEGORY_INFO_H_
 #define COMPONENTS_NTP_SNIPPETS_CATEGORY_INFO_H_
 
 #include "base/macros.h"
 #include "base/strings/string16.h"
 
 namespace ntp_snippets {
 
 // On Android builds, a Java counterpart will be generated for this enum.
 // GENERATED_JAVA_ENUM_PACKAGE: org.chromium.chrome.browser.ntp.snippets
 enum class ContentSuggestionsCardLayout {
   // Uses all fields.
   FULL_CARD,
 
   // No snippet_text and no thumbnail image.
   MINIMAL_CARD
 };
 
 // Contains static meta information about a Category.
 class CategoryInfo {
  public:
   CategoryInfo(const base::string16& title,
                ContentSuggestionsCardLayout card_layout,
                bool has_more_button,
-               bool show_if_empty);
+               bool show_if_empty,
+               const base::string16& no_suggestions_message);
   CategoryInfo(CategoryInfo&&) = default;
   CategoryInfo& operator=(CategoryInfo&&) = default;
 
   ~CategoryInfo();
 
   // Localized title of the category.
   const base::string16& title() const { return title_; }
 
   // Layout of the cards to be used to display suggestions in this category.
   ContentSuggestionsCardLayout card_layout() const { return card_layout_; }
 
   // Whether the category supports a "More" button. The button either triggers
   // a fixed action (like opening a native page) or, if there is no such fixed
   // action, it queries the provider for more suggestions.
   bool has_more_button() const { return has_more_button_; }

[Marc Treib, 2016/10/26 12:39:01]

(Unrelated to this change, but:) Both the comment and the name don't really
match what the UI does with this flag. It's really more of a
"show_more_button_if_not_empty" - should we rename it and update the
description? Also, should we maybe differentiate between "view all" (what we
have so far) and the actual "more" that fhorschig is working on in
https://codereview.chromium.org/2421463002/ ?

[dgn, 2016/10/26 14:05:40]

Yes, that would be a nice follow up CL. or "always_show_more_button"?

"More" is supposed to 3 things:

1. Go to some different UI to show all the [Bookmarks|Downloads|etc]
2. Fetch more suggestions, if we already have some
3. Reload the suggestions. Currently used only when we don't have any
suggestions.

I suppose 2. and 3. are more or less the same thing, but I don't know if we want
to let the categoryInfo specify things with such detail. We currently have the
behaviours hardcoded in the UI for each category.

And while we're on it, the UI does not do anything with card_layout from
categoryInfo at the moment.

[Marc Treib, 2016/10/26 14:29:09]

I updated the comment and added a TODO for now.
Exactly - I'm worried that it's super confusing when we use one term/flag for
three different things.
2 and 3 aren't quite the same thing. I'm not sure yet if we can treat them the
same here.
Anyway, that's for another day :)
Huh interesting - so how does the UI decide which layout to use? (I assume we
still want a reduced layout e.g. for downloads? Or is that just not
implemented?)

[dgn, 2016/10/26 16:00:33]

Oh nvm. It is directly provided from c++ when creating the suggestion. Only the
java field is not used.

 
   // Whether this category should be shown if it offers no suggestions.
   bool show_if_empty() const { return show_if_empty_; }
 
+  // The message to show if there are no suggestions in this category. Note that
+  // this matters even if |show_if_empty()| is false: The message still shows
+  // up when the user dismisses all suggestions in the category.
+  const base::string16& no_suggestions_message() const {
+    return no_suggestions_message_;
+  }
+
  private:
   base::string16 title_;
   ContentSuggestionsCardLayout card_layout_;
   bool has_more_button_;
   bool show_if_empty_;
+  base::string16 no_suggestions_message_;
 
   DISALLOW_COPY_AND_ASSIGN(CategoryInfo);
 };
 
 }  // namespace ntp_snippets
 
 #endif  // COMPONENTS_NTP_SNIPPETS_CATEGORY_INFO_H_