Make more clear representation of placeholder in notifications

app/src/main/java/com/keylesspalace/tusky/adapter/NotificationsAdapter.java

@@ -101,11 +101,19 @@ public class NotificationsAdapter extends RecyclerView.Adapter {
     public void onBindViewHolder(RecyclerView.ViewHolder viewHolder, int position) {
         if (position < notifications.size()) {
             NotificationViewData notification = notifications.get(position);
-            Notification.Type type = notification.getType();
+            if (notification instanceof NotificationViewData.Placeholder) {
+                NotificationViewData.Placeholder placeholder = ((NotificationViewData.Placeholder) notification);
+                PlaceholderViewHolder holder = (PlaceholderViewHolder) viewHolder;
+                holder.setup(!placeholder.isLoading(), statusListener);
+                return;
+            }
+            NotificationViewData.Concrete concreteNotificaton =
+                    (NotificationViewData.Concrete) notification;
+            Notification.Type type = concreteNotificaton.getType();
             switch (type) {
                 case MENTION: {
                     StatusViewHolder holder = (StatusViewHolder) viewHolder;
-                    StatusViewData status = notification.getStatusViewData();
+                    StatusViewData status = concreteNotificaton.getStatusViewData();
                     holder.setupWithStatus(status,
                             statusListener, mediaPreviewEnabled);
                     break;
@@ -113,23 +121,18 @@ public class NotificationsAdapter extends RecyclerView.Adapter {
                 case FAVOURITE:
                 case REBLOG: {
                     StatusNotificationViewHolder holder = (StatusNotificationViewHolder) viewHolder;
-                    holder.setMessage(type, notification.getAccount().getDisplayName(),
+                    holder.setMessage(type, concreteNotificaton.getAccount().getDisplayName(),
-                            notification.getStatusViewData());
+                            concreteNotificaton.getStatusViewData());
-                    holder.setupButtons(notificationActionListener, notification.getAccount().id);
+                    holder.setupButtons(notificationActionListener, concreteNotificaton.getAccount().id);
-                    holder.setAvatars(notification.getStatusViewData().getAvatar(),
+                    holder.setAvatars(concreteNotificaton.getStatusViewData().getAvatar(),
-                            notification.getAccount().avatar);
+                            concreteNotificaton.getAccount().avatar);
                     break;
                 }
                 case FOLLOW: {
                     FollowViewHolder holder = (FollowViewHolder) viewHolder;
-                    holder.setMessage(notification.getAccount().getDisplayName(),
+                    holder.setMessage(concreteNotificaton.getAccount().getDisplayName(),
-                            notification.getAccount().username, notification.getAccount().avatar);
+                            concreteNotificaton.getAccount().username, concreteNotificaton.getAccount().avatar);
-                    holder.setupButtons(notificationActionListener, notification.getAccount().id);
+                    holder.setupButtons(notificationActionListener, concreteNotificaton.getAccount().id);
-                    break;
-                }
-                case PLACEHOLDER: {
-                    PlaceholderViewHolder holder = (PlaceholderViewHolder) viewHolder;
-                    holder.setup(!notification.isPlaceholderLoading(), statusListener);
                     break;
                 }
             }
@@ -150,21 +153,25 @@ public class NotificationsAdapter extends RecyclerView.Adapter {
             return VIEW_TYPE_FOOTER;
         } else {
             NotificationViewData notification = notifications.get(position);
-            switch (notification.getType()) {
+            if (notification instanceof NotificationViewData.Concrete) {
-                default:
+                NotificationViewData.Concrete concrete = ((NotificationViewData.Concrete) notification);
-                case MENTION: {
+                switch (concrete.getType()) {
-                    return VIEW_TYPE_MENTION;
+                    default:
-                }
+                    case MENTION: {
-                case FAVOURITE:
+                        return VIEW_TYPE_MENTION;
-                case REBLOG: {
+                    }
-                    return VIEW_TYPE_STATUS_NOTIFICATION;
+                    case FAVOURITE:
-                }
+                    case REBLOG: {
-                case FOLLOW: {
+                        return VIEW_TYPE_STATUS_NOTIFICATION;
-                    return VIEW_TYPE_FOLLOW;
+                    }
-                }
+                    case FOLLOW: {
-                case PLACEHOLDER: {
+                        return VIEW_TYPE_FOLLOW;
-                    return VIEW_TYPE_PLACEHOLDER;
+                    }
                 }
+            } else if (notification instanceof NotificationViewData.Placeholder) {
+                return VIEW_TYPE_PLACEHOLDER;
+            } else {
+                throw new AssertionError("Unknown notification type");
             }
         }
     }

app/src/main/java/com/keylesspalace/tusky/entity/Notification.java

@@ -27,7 +27,6 @@ public class Notification {
         FAVOURITE,
         @SerializedName("follow")
         FOLLOW,
-        PLACEHOLDER
     }
 
     public Type type;

app/src/main/java/com/keylesspalace/tusky/fragment/NotificationsFragment.java

@@ -44,6 +44,8 @@ import com.keylesspalace.tusky.entity.Status;
 import com.keylesspalace.tusky.interfaces.ActionButtonActivity;
 import com.keylesspalace.tusky.interfaces.StatusActionListener;
 import com.keylesspalace.tusky.receiver.TimelineReceiver;
+import com.keylesspalace.tusky.util.CollectionUtil;
+import com.keylesspalace.tusky.util.Either;
 import com.keylesspalace.tusky.util.HttpHeaderLink;
 import com.keylesspalace.tusky.util.ListUtils;
 import com.keylesspalace.tusky.util.PairedList;
@@ -74,6 +76,21 @@ public class NotificationsFragment extends SFragment implements
         MIDDLE
     }
 
+    /**
+     * Placeholder for the notifications. Consider moving to the separate class to hide constructor
+     * and reuse in different places as needed.
+     */
+    private static final class Placeholder {
+        private static final Placeholder INSTANCE = new Placeholder();
+
+        public static Placeholder getInstance() {
+            return INSTANCE;
+        }
+
+        private Placeholder() {
+        }
+    }
+
     private SwipeRefreshLayout swipeRefreshLayout;
     private LinearLayoutManager layoutManager;
     private RecyclerView recyclerView;
@@ -89,11 +106,17 @@ public class NotificationsFragment extends SFragment implements
     private String bottomId;
     private String topId;
 
-    private final PairedList<Notification, NotificationViewData> notifications
+    // Each element is either a Notification for loading data or a Placeholder
-            = new PairedList<>(new Function<Notification, NotificationViewData>() {
+    private final PairedList<Either<Placeholder, Notification>, NotificationViewData> notifications
+            = new PairedList<>(new Function<Either<Placeholder, Notification>, NotificationViewData>() {
         @Override
-        public NotificationViewData apply(Notification input) {
+        public NotificationViewData apply(Either<Placeholder, Notification> input) {
-            return ViewDataUtils.notificationToViewData(input);
+            if (input.isRight()) {
+                Notification notification = input.getAsRight();
+                return ViewDataUtils.notificationToViewData(notification);
+            } else {
+                return new NotificationViewData.Placeholder(false);
+            }
         }
     });
 
@@ -185,7 +208,7 @@ public class NotificationsFragment extends SFragment implements
                 ActionButtonActivity activity = (ActionButtonActivity) getActivity();
                 FloatingActionButton composeButton = activity.getActionButton();
 
-                if(composeButton != null) {
+                if (composeButton != null) {
                     if (hideFab) {
                         if (dy > 0 && composeButton.isShown()) {
                             composeButton.hide(); // hides the button if we're scrolling down
@@ -225,13 +248,12 @@ public class NotificationsFragment extends SFragment implements
 
     @Override
     public void onReply(int position) {
-        Notification notification = notifications.get(position);
+        super.reply(notifications.get(position).getAsRight().status);
-        super.reply(notification.status);
     }
 
     @Override
     public void onReblog(final boolean reblog, final int position) {
-        final Notification notification = notifications.get(position);
+        final Notification notification = notifications.get(position).getAsRight();
         final Status status = notification.status;
         reblogWithCallback(status, reblog, new Callback<Status>() {
             @Override
@@ -242,7 +264,9 @@ public class NotificationsFragment extends SFragment implements
                     if (status.reblog != null) {
                         status.reblog.reblogged = reblog;
                     }
-                    notifications.set(position, notification);
+                    // Java's type inference *eyeroll*
+                    notifications.set(position,
+                            Either.<Placeholder, Notification>right(notification));
 
                     adapter.updateItemWithNotify(position, notifications.getPairedItem(position), true);
 
@@ -260,7 +284,7 @@ public class NotificationsFragment extends SFragment implements
 
     @Override
     public void onFavourite(final boolean favourite, final int position) {
-        final Notification notification = notifications.get(position);
+        final Notification notification = notifications.get(position).getAsRight();
         final Status status = notification.status;
         favouriteWithCallback(status, favourite, new Callback<Status>() {
             @Override
@@ -272,7 +296,8 @@ public class NotificationsFragment extends SFragment implements
                         status.reblog.favourited = favourite;
                     }
 
-                    notifications.set(position, notification);
+                    notifications.set(position,
+                            Either.<Placeholder, Notification>right(notification));
 
                     adapter.updateItemWithNotify(position, notifications.getPairedItem(position), true);
 
@@ -289,7 +314,7 @@ public class NotificationsFragment extends SFragment implements
 
     @Override
     public void onMore(View view, int position) {
-        Notification notification = notifications.get(position);
+        Notification notification = notifications.get(position).getAsRight();
         super.more(notification.status, view, position);
     }
 
@@ -301,38 +326,40 @@ public class NotificationsFragment extends SFragment implements
 
     @Override
     public void onViewThread(int position) {
-        Notification notification = notifications.get(position);
+        Notification notification = notifications.get(position).getAsRight();
         super.viewThread(notification.status);
     }
 
     @Override
     public void onOpenReblog(int position) {
-        Notification notification = notifications.get(position);
+        Notification notification = notifications.get(position).getAsRight();
-        if (notification != null) onViewAccount(notification.account.id);
+        onViewAccount(notification.account.id);
     }
 
     @Override
     public void onExpandedChange(boolean expanded, int position) {
-        NotificationViewData old = notifications.getPairedItem(position);
+        NotificationViewData.Concrete old =
+                (NotificationViewData.Concrete) notifications.getPairedItem(position);
         StatusViewData statusViewData =
                 new StatusViewData.Builder(old.getStatusViewData())
                         .setIsExpanded(expanded)
                         .createStatusViewData();
-        NotificationViewData notificationViewData = new NotificationViewData(old.getType(),
+        NotificationViewData notificationViewData = new NotificationViewData.Concrete(old.getType(),
-                old.getId(), old.getAccount(), statusViewData, false);
+                old.getId(), old.getAccount(), statusViewData);
         notifications.setPairedItem(position, notificationViewData);
         adapter.updateItemWithNotify(position, notificationViewData, false);
     }
 
     @Override
     public void onContentHiddenChange(boolean isShowing, int position) {
-        NotificationViewData old = notifications.getPairedItem(position);
+        NotificationViewData.Concrete old =
+                (NotificationViewData.Concrete) notifications.getPairedItem(position);
         StatusViewData statusViewData =
                 new StatusViewData.Builder(old.getStatusViewData())
                         .setIsShowingSensitiveContent(isShowing)
                         .createStatusViewData();
-        NotificationViewData notificationViewData = new NotificationViewData(old.getType(),
+        NotificationViewData notificationViewData = new NotificationViewData.Concrete(old.getType(),
-                old.getId(), old.getAccount(), statusViewData, false);
+                old.getId(), old.getAccount(), statusViewData);
         notifications.setPairedItem(position, notificationViewData);
         adapter.updateItemWithNotify(position, notificationViewData, false);
     }
@@ -341,13 +368,12 @@ public class NotificationsFragment extends SFragment implements
     public void onLoadMore(int position) {
         //check bounds before accessing list,
         if (notifications.size() >= position && position > 0) {
-            String fromId = notifications.get(position - 1).id;
+            // is it safe?
-            String toId = notifications.get(position + 1).id;
+            String fromId = notifications.get(position - 1).getAsRight().id;
+            String toId = notifications.get(position + 1).getAsRight().id;
             sendFetchNotificationsRequest(fromId, toId, FetchEnd.MIDDLE, position);
-
+            NotificationViewData notificationViewData =
-            NotificationViewData old = notifications.getPairedItem(position);
+                    new NotificationViewData.Placeholder(true);
-            NotificationViewData notificationViewData = new NotificationViewData(old.getType(),
-                    old.getId(), old.getAccount(), old.getStatusViewData(), true);
             notifications.setPairedItem(position, notificationViewData);
             adapter.updateItemWithNotify(position, notificationViewData, false);
         } else {
@@ -390,10 +416,11 @@ public class NotificationsFragment extends SFragment implements
     @Override
     public void removeAllByAccountId(String accountId) {
         // using iterator to safely remove items while iterating
-        Iterator<Notification> iterator = notifications.iterator();
+        Iterator<Either<Placeholder, Notification>> iterator = notifications.iterator();
         while (iterator.hasNext()) {
-            Notification notification = iterator.next();
+            Either<Placeholder, Notification> notification = iterator.next();
-            if (notification.account.id.equals(accountId)) {
+            Notification maybeNotification = notification.getAsRightOrNull();
+            if (maybeNotification != null && maybeNotification.account.id.equals(accountId)) {
                 iterator.remove();
             }
         }
@@ -470,7 +497,7 @@ public class NotificationsFragment extends SFragment implements
                 break;
             }
             case MIDDLE: {
-                insert(notifications, pos);
+                replacePlaceholderWithNotifications(notifications, pos);
                 break;
             }
             case BOTTOM: {
@@ -520,24 +547,25 @@ public class NotificationsFragment extends SFragment implements
         if (uptoId != null) {
             topId = uptoId;
         }
+        List<Either<Placeholder, Notification>> liftedNew =
+                liftNotificationList(newNotifications);
         if (notifications.isEmpty()) {
-            notifications.addAll(newNotifications);
+            notifications.addAll(liftedNew);
         } else {
-            int index = notifications.indexOf(newNotifications.get(newNotifications.size() - 1));
+            int index = notifications.indexOf(liftedNew.get(newNotifications.size() - 1));
             for (int i = 0; i < index; i++) {
                 notifications.remove(0);
             }
-            int newIndex = newNotifications.indexOf(notifications.get(0));
+
+
+            int newIndex = liftedNew.indexOf(notifications.get(0));
             if (newIndex == -1) {
-                if(index == -1 && newNotifications.size() >= LOAD_AT_ONCE) {
+                if (index == -1 && liftedNew.size() >= LOAD_AT_ONCE) {
-                    Notification placeholder = new Notification();
+                    liftedNew.add(Either.<Placeholder, Notification>left(Placeholder.getInstance()));
-                    placeholder.type = Notification.Type.PLACEHOLDER;
-                    newNotifications.add(placeholder);
                 }
-                notifications.addAll(0, newNotifications);
+                notifications.addAll(0, liftedNew);
             } else {
-                List<Notification> sublist = newNotifications.subList(0, newIndex);
+                notifications.addAll(0, liftedNew.subList(0, newIndex));
-                notifications.addAll(0, sublist);
             }
         }
         adapter.update(notifications.getPairedCopy());
@@ -551,9 +579,10 @@ public class NotificationsFragment extends SFragment implements
             bottomId = fromId;
         }
         int end = notifications.size();
-        Notification last = notifications.get(end - 1);
+        List<Either<Placeholder, Notification>> liftedNew = liftNotificationList(newNotifications);
-        if (last != null && !findNotification(newNotifications, last.id)) {
+        Either<Placeholder, Notification> last = notifications.get(end - 1);
-            notifications.addAll(newNotifications);
+        if (last != null && liftedNew.indexOf(last) == -1) {
+            notifications.addAll(liftedNew);
             List<NotificationViewData> newViewDatas = notifications.getPairedCopy()
                     .subList(notifications.size() - newNotifications.size(),
                             notifications.size());
@@ -561,23 +590,14 @@ public class NotificationsFragment extends SFragment implements
         }
     }
 
-    private static boolean findNotification(List<Notification> notifications, String id) {
-        for (Notification notification : notifications) {
-            if (notification.id.equals(id)) {
-                return true;
-            }
-        }
-        return false;
-    }
 
     private void onFetchNotificationsFailure(Exception exception, FetchEnd fetchEnd, int position) {
         swipeRefreshLayout.setRefreshing(false);
-        if(fetchEnd == FetchEnd.MIDDLE && notifications.getPairedItem(position).getType() == Notification.Type.PLACEHOLDER) {
+        if (fetchEnd == FetchEnd.MIDDLE && !notifications.get(position).isRight()) {
-            NotificationViewData old = notifications.getPairedItem(position);
+            NotificationViewData placeholderVD =
-            NotificationViewData notificationViewData = new NotificationViewData(old.getType(),
+                    new NotificationViewData.Placeholder(false);
-                    old.getId(), old.getAccount(), old.getStatusViewData(), false);
+            notifications.setPairedItem(position, placeholderVD);
-            notifications.setPairedItem(position, notificationViewData);
+            adapter.updateItemWithNotify(position, placeholderVD, true);
-            adapter.updateItemWithNotify(position, notificationViewData, true);
         }
         Log.e(TAG, "Fetch failure: " + exception.getMessage());
         fulfillAnyQueuedFetches(fetchEnd);
@@ -604,8 +624,8 @@ public class NotificationsFragment extends SFragment implements
         }
     }
 
-    private void insert(List<Notification> newNotifications, int pos) {
+    private void replacePlaceholderWithNotifications(List<Notification> newNotifications, int pos) {
-
+        // Remove placeholder
         notifications.remove(pos);
 
         if (ListUtils.isEmpty(newNotifications)) {
@@ -613,15 +633,29 @@ public class NotificationsFragment extends SFragment implements
             return;
         }
 
-        if(newNotifications.size() >= LOAD_AT_ONCE) {
+        List<Either<Placeholder, Notification>> liftedNew = liftNotificationList(newNotifications);
-            Notification placeholder = new Notification();
+
-            placeholder.type = Notification.Type.PLACEHOLDER;
+        // If we fetched less posts than in the limit, it means that the hole is not filled
-            newNotifications.add(placeholder);
+        // If we fetched at least as much it means that there are more posts to load and we should
+        // insert new placeholder
+        if (newNotifications.size() >= LOAD_AT_ONCE) {
+            liftedNew.add(Either.<Placeholder, Notification>left(Placeholder.getInstance()));
         }
 
-        notifications.addAll(pos, newNotifications);
+        notifications.addAll(pos, liftedNew);
         adapter.update(notifications.getPairedCopy());
+    }
 
+    private final Function<Notification, Either<Placeholder, Notification>> notificationLifter =
+            new Function<Notification, Either<Placeholder, Notification>>() {
+                @Override
+                public Either<Placeholder, Notification> apply(Notification input) {
+                    return Either.right(input);
+                }
+            };
+
+    private List<Either<Placeholder, Notification>> liftNotificationList(List<Notification> list) {
+        return CollectionUtil.map(list, notificationLifter);
     }
 
     private void fullyRefresh() {

app/src/main/java/com/keylesspalace/tusky/util/CollectionUtil.java

@@ -0,0 +1,38 @@
+/* Copyright 2017 Andrew Dawson
+ *
+ * This file is a part of Tusky.
+ *
+ * This program is free software; you can redistribute it and/or modify it under the terms of the
+ * GNU General Public License as published by the Free Software Foundation; either version 3 of the
+ * License, or (at your option) any later version.
+ *
+ * Tusky is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even
+ * the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General
+ * Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License along with Tusky; if not,
+ * see <http://www.gnu.org/licenses>. */
+package com.keylesspalace.tusky.util;
+
+import android.arch.core.util.Function;
+
+import java.util.ArrayList;
+import java.util.List;
+
+/**
+ * Created by charlag on 05/11/17.
+ */
+
+public final class CollectionUtil {
+    private CollectionUtil() {
+        throw new AssertionError();
+    }
+
+    public static <E, R> List<R> map(List<E> list, Function<E, R> mapper) {
+        final List<R> newList = new ArrayList<>(list.size());
+        for (E el : list) {
+            newList.add(mapper.apply(el));
+        }
+        return newList;
+    }
+}

app/src/main/java/com/keylesspalace/tusky/util/Either.java

@@ -0,0 +1,125 @@
+/* Copyright 2017 Andrew Dawson
+ *
+ * This file is a part of Tusky.
+ *
+ * This program is free software; you can redistribute it and/or modify it under the terms of the
+ * GNU General Public License as published by the Free Software Foundation; either version 3 of the
+ * License, or (at your option) any later version.
+ *
+ * Tusky is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even
+ * the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General
+ * Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License along with Tusky; if not,
+ * see <http://www.gnu.org/licenses>. */
+package com.keylesspalace.tusky.util;
+
+import android.support.annotation.NonNull;
+import android.support.annotation.Nullable;
+
+/**
+ * Created by charlag on 05/11/17.
+ *
+ * Class to represent sum type/tagged union/variant/ADT e.t.c.
+ * It is either Left or Right.
+ */
+public final class Either<L, R> {
+
+    /**
+     * Constructs Left instance of either
+     * @param left Object to be considered Left
+     * @param <L> Left type
+     * @param <R> Right type
+     * @return new instance of Either which contains left.
+     */
+    public static <L, R> Either<L, R> left(L left) {
+        return new Either<>(left, false);
+    }
+
+    /**
+     * Constructs Right instance of either
+     * @param right Object to be considered Right
+     * @param <L> Left type
+     * @param <R> Right type
+     * @return new instance of Either which contains right.
+     */
+    public static <L, R> Either<L, R> right(R right) {
+        return new Either<>(right, true);
+    }
+
+    private final Object value;
+    // we need it because of the types erasure
+    private boolean isRight;
+
+    private Either(Object value, boolean isRight) {
+        this.value = value;
+        this.isRight = isRight;
+    }
+
+    public boolean isRight() {
+        return isRight;
+    }
+
+    /**
+     * Try to get contained object as a Left or throw an exception.
+     * @throws AssertionError If contained value is Right
+     * @return contained value as Right
+     */
+    public @NonNull L getAsLeft() {
+        if (isRight) {
+            throw new AssertionError("Tried to get the Either as Left while it is Right");
+        }
+        //noinspection unchecked
+        return (L) value;
+    }
+
+    /**
+     * Try to get contained object as a Right or throw an exception.
+     * @throws AssertionError If contained value is Left
+     * @return contained value as Right
+     */
+    public @NonNull R getAsRight() {
+        if (!isRight) {
+            throw new AssertionError("Tried to get the Either as Right while it is Left");
+        }
+        //noinspection unchecked
+        return (R) value;
+    }
+
+    /**
+     * Same as {@link #getAsLeft()} but returns {@code null} is the value if Right instead of
+     * throwing an exception.
+     * @return contained value as Left or null
+     */
+    public @Nullable L getAsLeftOrNull() {
+        if (isRight) {
+            return null;
+        }
+        //noinspection unchecked
+        return (L) value;
+    }
+
+    /**
+     * Same as {@link #getAsRightOrNull()} but returns {@code null} is the value if Left instead of
+     * throwing an exception.
+     * @return contained value as Right or null
+     */
+    public @Nullable R getAsRightOrNull() {
+        if (!isRight) {
+            return null;
+        }
+        //noinspection unchecked
+        return (R) value;
+    }
+
+    @Override
+    public boolean equals(Object obj) {
+        if (this == obj) return true;
+        if (obj == null) return false;
+        if (!(obj instanceof Either)) return false;
+        Either that = (Either) obj;
+        return this.isRight == that.isRight &&
+                (this.value == that.value ||
+                        this.value != null && this.value.equals(that.value));
+    }
+}

app/src/main/java/com/keylesspalace/tusky/util/ViewDataUtils.java

@@ -34,7 +34,7 @@ public final class ViewDataUtils {
     @Nullable
     public static StatusViewData statusToViewData(@Nullable Status status) {
         if (status == null) return null;
-        if(status.placeholder) {
+        if (status.placeholder) {
             return new StatusViewData.Builder().setId(status.id)
                     .setPlaceholder(true)
                     .createStatusViewData();
@@ -80,8 +80,8 @@ public final class ViewDataUtils {
     }
 
     public static NotificationViewData notificationToViewData(Notification notification) {
-        return new NotificationViewData(notification.type, notification.id, notification.account,
+        return new NotificationViewData.Concrete(notification.type, notification.id, notification.account,
-                statusToViewData(notification.status), false);
+                statusToViewData(notification.status));
     }
 
     public static List<NotificationViewData> notificationListToViewDataList(

app/src/main/java/com/keylesspalace/tusky/viewdata/NotificationViewData.java

@@ -20,41 +20,59 @@ import com.keylesspalace.tusky.entity.Notification;
 
 /**
  * Created by charlag on 12/07/2017.
+ *
+ * Class to represent data required to display either a notification or a placeholder.
+ * It is either a {@link Placeholder} or a {@link Concrete}.
+ * It is modelled this way because close relationship between placeholder and concrete notification
+ * is fine in this case. Placeholder case is not modelled as a type of notification because
+ * invariants would be violated and because it would model domain incorrectly. It is prefereable to
+ * {@link com.keylesspalace.tusky.util.Either} because class hierarchy is cheaper, faster and
+ * more native.
  */
-
+public abstract class NotificationViewData {
-public final class NotificationViewData {
+    private NotificationViewData() {
-    private final Notification.Type type;
-    private final String id;
-    private final Account account;
-    private final StatusViewData statusViewData;
-    private final boolean placeholderLoading;
-
-    public NotificationViewData(Notification.Type type, String id, Account account,
-                                StatusViewData statusViewData, boolean placeholderLoading) {
-        this.type = type;
-        this.id = id;
-        this.account = account;
-        this.statusViewData = statusViewData;
-        this.placeholderLoading = placeholderLoading;
     }
 
-    public Notification.Type getType() {
+    public static  final class Concrete extends NotificationViewData {
-        return type;
+        private final Notification.Type type;
+        private final String id;
+        private final Account account;
+        private final StatusViewData statusViewData;
+
+        public Concrete(Notification.Type type, String id, Account account,
+                        StatusViewData statusViewData) {
+            this.type = type;
+            this.id = id;
+            this.account = account;
+            this.statusViewData = statusViewData;
+        }
+
+        public Notification.Type getType() {
+            return type;
+        }
+
+        public String getId() {
+            return id;
+        }
+
+        public Account getAccount() {
+            return account;
+        }
+
+        public StatusViewData getStatusViewData() {
+            return statusViewData;
+        }
     }
 
-    public String getId() {
+    public static final class Placeholder extends NotificationViewData {
-        return id;
+        private final boolean isLoading;
-    }
 
-    public Account getAccount() {
+        public Placeholder(boolean isLoading) {
-        return account;
+            this.isLoading = isLoading;
-    }
+        }
 
-    public StatusViewData getStatusViewData() {
+        public boolean isLoading() {
-        return statusViewData;
+            return isLoading;
-    }
+        }
-
-    public boolean isPlaceholderLoading() {
-        return placeholderLoading;
     }
 }