Support undoing offline page deletion

chrome/android/java/src/org/chromium/chrome/browser/enhancedbookmarks/EnhancedBookmarkItemsAdapter.java

Index: chrome/android/java/src/org/chromium/chrome/browser/enhancedbookmarks/EnhancedBookmarkItemsAdapter.java
diff --git a/chrome/android/java/src/org/chromium/chrome/browser/enhancedbookmarks/EnhancedBookmarkItemsAdapter.java b/chrome/android/java/src/org/chromium/chrome/browser/enhancedbookmarks/EnhancedBookmarkItemsAdapter.java
index 8581b8ddd34c598c9e7ebffbd1058fa098160efb..88b8c500320e350fcfb602b9767c79af956dc7d4 100644
--- a/chrome/android/java/src/org/chromium/chrome/browser/enhancedbookmarks/EnhancedBookmarkItemsAdapter.java
+++ b/chrome/android/java/src/org/chromium/chrome/browser/enhancedbookmarks/EnhancedBookmarkItemsAdapter.java
@@ -18,6 +18,7 @@ import org.chromium.chrome.browser.BookmarksBridge.BookmarkModelObserver;
 import org.chromium.chrome.browser.enhancedbookmarks.EnhancedBookmarkManager.UIState;
 import org.chromium.chrome.browser.enhancedbookmarks.EnhancedBookmarkPromoHeader.PromoHeaderShowingChangeListener;
 import org.chromium.chrome.browser.offlinepages.OfflinePageBridge;
+import org.chromium.chrome.browser.offlinepages.OfflinePageBridge.OfflinePageModelObserver;
 import org.chromium.chrome.browser.offlinepages.OfflinePageFreeUpSpaceCallback;
 import org.chromium.chrome.browser.offlinepages.OfflinePageFreeUpSpaceDialog;
 import org.chromium.chrome.browser.offlinepages.OfflinePageStorageSpaceHeader;
@@ -77,6 +78,8 @@ class EnhancedBookmarkItemsAdapter extends RecyclerView.Adapter<RecyclerView.Vie
         }
     };
 
+    private OfflinePageModelObserver mOfflinePageModelObserver;
+
     EnhancedBookmarkItemsAdapter(Context context) {
         mContext = context;
 
@@ -272,6 +275,14 @@ class EnhancedBookmarkItemsAdapter extends RecyclerView.Adapter<RecyclerView.Vie
         mPromoHeaderManager = new EnhancedBookmarkPromoHeader(mContext, this);
         OfflinePageBridge offlinePageBridge = mDelegate.getModel().getOfflinePageBridge();
         if (offlinePageBridge != null) {
+            mOfflinePageModelObserver = new OfflinePageModelObserver() {
+                @Override
+                public void offlinePageModelChanged() {
+                    mDelegate.notifyStateChange(EnhancedBookmarkItemsAdapter.this);

[Ian Wen, 2015/10/14 23:30:01]

1. Is offline model change capable of removing/adding bookmarks? If not, I would
use notifyDataSetChanged() here.

EBDelegate#notifyStateChange() will let bookmark model regenerate the list of
bookmarks to show. Instead, notifyDataSetChange() only tells recycler view to
relayout all items.

2. It seems offlinePageModelChanged() might be called after offlinepage model is
loaded. If we iniatialize the offline page during EB's initialization, we might
end up having to refresh this adapter twice (once for EB's loading, once for
offline page). Are there better designs to prevent this refresh-twice problem?

[jianli, 2015/10/14 23:40:48]

We need to call notifyStateChange, since relayout provided by
notifyDataSetChange is not enough because the removed items will reappear here.
OfflinePageModelChanged will only be fired after the model is loaded and there
is a request to add/remove/update offline page items, mostly due to user action.
So it means that we do need to refresh the UI per the user action for most of
the cases. In the rare case of bookmark sync, this is likely but probably we
don't want to handle it.

[Ian Wen, 2015/10/15 00:02:16]

Hmm I saw another CL that adds delete signals to the model observer. If delete
is handled specifically, are there other reasons that we want to use
notifyStateChange()?

[jianli, 2015/10/15 00:05:26]

Yes, we need it for undoing the bookmark deletion that will also bring the
offline page back.

+                }
+            };
+            offlinePageBridge.addObserver(mOfflinePageModelObserver);
+
             mOfflineStorageHeader = new OfflinePageStorageSpaceHeader(
                     mContext, offlinePageBridge, new OfflinePageFreeUpSpaceCallback() {
                         @Override
@@ -295,7 +306,10 @@ class EnhancedBookmarkItemsAdapter extends RecyclerView.Adapter<RecyclerView.Vie
         mDelegate.removeUIObserver(this);
         mDelegate.getModel().removeObserver(mBookmarkModelObserver);
         mPromoHeaderManager.destroy();
-        if (mOfflineStorageHeader != null) {
+
+        OfflinePageBridge offlinePageBridge = mDelegate.getModel().getOfflinePageBridge();
+        if (offlinePageBridge != null) {
+            offlinePageBridge.removeObserver(mOfflinePageModelObserver);
             mOfflineStorageHeader.destroy();
         }
     }