Added pager for chat messages to prevent long loading time

src/android/org/linphone/chat/ChatEventsAdapter.java

@@ -69,6 +69,7 @@ import java.io.IOException;
 import java.lang.ref.WeakReference;
 import java.util.ArrayList;
 import java.util.Arrays;
+import java.util.Collections;
 import java.util.List;
 
 import static android.content.Intent.FLAG_GRANT_READ_URI_PERMISSION;
@@ -93,6 +94,7 @@ public class ChatEventsAdapter extends SelectableAdapter<ChatBubbleViewHolder> {
         mContext = mFragment.getActivity();
         mItemResource = itemResource;
         mHistory = new ArrayList<>(Arrays.asList(history));
+        Collections.reverse(mHistory);
         mParticipants = participants;
         mClickListener = clickListener;
         mListener = new ChatMessageListenerStub() {
@@ -414,9 +416,16 @@ public class ChatEventsAdapter extends SelectableAdapter<ChatBubbleViewHolder> {
     }
 
     public void addToHistory(EventLog log) {
-        mHistory.add(log);
+        notifyItemChanged(0);
-        notifyDataSetChanged();
+        mHistory.add(0, log);
+        notifyItemInserted(0);
+    }
 
+    public void addAllToHistory(ArrayList<EventLog> logs) {
+        int currentSize = mHistory.size() - 1;
+        Collections.reverse(logs);
+        mHistory.addAll(logs);
+        notifyItemRangeInserted(currentSize + 1, logs.size());
     }
 
     public void setContacts(ArrayList<LinphoneContact> participants) {
@@ -425,6 +434,7 @@ public class ChatEventsAdapter extends SelectableAdapter<ChatBubbleViewHolder> {
 
     public void refresh(EventLog[] history) {
         mHistory = new ArrayList<>(Arrays.asList(history));
+        Collections.reverse(mHistory);
         notifyDataSetChanged();
     }
 

src/android/org/linphone/chat/ChatScrollListener.java

@@ -0,0 +1,104 @@
+package org.linphone.chat;
+
+/*
+ChatScrollListener.java
+Copyright (C) 2010-2018  Belledonne Communications, Grenoble, France
+
+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 2
+of the License, or (at your option) any later version.
+
+This program 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 this program; if not, write to the Free Software
+Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA.
+*/
+
+import android.support.v7.widget.LinearLayoutManager;
+import android.support.v7.widget.RecyclerView;
+
+public abstract class ChatScrollListener extends RecyclerView.OnScrollListener {
+    // The minimum amount of items to have below your current scroll position
+    // before loading more.
+    private int visibleThreshold = 5;
+    // The current offset index of data you have loaded
+    private int currentPage = 0;
+    // The total number of items in the dataset after the last load
+    private int previousTotalItemCount = 0;
+    // True if we are still waiting for the last set of data to load.
+    private boolean loading = true;
+    // Sets the starting page index
+    private int startingPageIndex = 0;
+
+    private LinearLayoutManager mLayoutManager;
+
+    public ChatScrollListener(LinearLayoutManager layoutManager) {
+        mLayoutManager = layoutManager;
+    }
+
+    public int getLastVisibleItem(int[] lastVisibleItemPositions) {
+        int maxSize = 0;
+        for (int i = 0; i < lastVisibleItemPositions.length; i++) {
+            if (i == 0) {
+                maxSize = lastVisibleItemPositions[i];
+            }
+            else if (lastVisibleItemPositions[i] > maxSize) {
+                maxSize = lastVisibleItemPositions[i];
+            }
+        }
+        return maxSize;
+    }
+
+    // This happens many times a second during a scroll, so be wary of the code you place here.
+    // We are given a few useful parameters to help us work out if we need to load some more data,
+    // but first we check if we are waiting for the previous load to finish.
+    @Override
+    public void onScrolled(RecyclerView view, int dx, int dy) {
+        int lastVisibleItemPosition = 0;
+        int totalItemCount = mLayoutManager.getItemCount();
+
+        lastVisibleItemPosition = mLayoutManager.findLastVisibleItemPosition();
+
+        // If the total item count is zero and the previous isn't, assume the
+        // list is invalidated and should be reset back to initial state
+        if (totalItemCount < previousTotalItemCount) {
+            this.currentPage = this.startingPageIndex;
+            this.previousTotalItemCount = totalItemCount;
+            if (totalItemCount == 0) {
+                this.loading = true;
+            }
+        }
+        // If it’s still loading, we check to see if the dataset count has
+        // changed, if so we conclude it has finished loading and update the current page
+        // number and total item count.
+        if (loading && (totalItemCount > previousTotalItemCount)) {
+            loading = false;
+            previousTotalItemCount = totalItemCount;
+        }
+
+        // If it isn’t currently loading, we check to see if we have breached
+        // the visibleThreshold and need to reload more data.
+        // If we do need to reload some more data, we execute onLoadMore to fetch the data.
+        // threshold should reflect how many total columns there are too
+        if (!loading && (lastVisibleItemPosition + visibleThreshold) > totalItemCount) {
+            currentPage++;
+            onLoadMore(currentPage, totalItemCount, view);
+            loading = true;
+        }
+    }
+
+    // Call this method whenever performing new searches
+    public void resetState() {
+        this.currentPage = this.startingPageIndex;
+        this.previousTotalItemCount = 0;
+        this.loading = true;
+    }
+
+    // Defines the process for actually loading more data based on page
+    public abstract void onLoadMore(int page, int totalItemsCount, RecyclerView view);
+}

src/android/org/linphone/chat/GroupChatFragment.java

@@ -32,6 +32,8 @@ import android.graphics.Rect;
 import android.net.Uri;
 import android.os.Bundle;
 import android.os.Environment;
+import android.os.Handler;
+import android.os.Looper;
 import android.os.Parcelable;
 import android.provider.MediaStore;
 import android.support.v7.widget.LinearLayoutManager;
@@ -80,6 +82,8 @@ import org.linphone.ui.SelectableHelper;
 
 import java.io.File;
 import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.Collections;
 import java.util.List;
 
 import static android.content.Context.INPUT_METHOD_SERVICE;
@@ -87,7 +91,9 @@ import static org.linphone.fragments.FragmentsAvailable.CHAT;
 
 public class GroupChatFragment extends Fragment implements ChatRoomListener, ContactsUpdatedListener, ChatBubbleViewHolder.ClickListener, SelectableHelper.DeleteListener {
     private static final int ADD_PHOTO = 1337;
+    private static final int MESSAGES_PER_PAGE = 20;
 
+    private Handler mHandler = new Handler(Looper.getMainLooper());
     private ImageView mBackButton, mCallButton, mBackToCallButton, mGroupInfosButton;
     private ImageView mAttachImageButton, mSendMessageButton;
     private TextView mRoomLabel, mParticipantsLabel, mRemoteComposing;
@@ -106,6 +112,7 @@ public class GroupChatFragment extends Fragment implements ChatRoomListener, Con
     private ArrayList<LinphoneContact> mParticipants;
     private LinearLayoutManager layoutManager;
     private int mContextMenuMessagePosition;
+    private ChatScrollListener mChatScrollListener;
 
     @Override
     public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
@@ -218,9 +225,17 @@ public class GroupChatFragment extends Fragment implements ChatRoomListener, Con
 
         mChatEventsList = view.findViewById(R.id.chat_message_list);
         mSelectionHelper = new SelectableHelper(view, this);
-        layoutManager = new LinearLayoutManager(mContext);
+        layoutManager = new LinearLayoutManager(mContext, LinearLayoutManager.VERTICAL, true);
         mChatEventsList.setLayoutManager(layoutManager);
 
+        mChatScrollListener = new ChatScrollListener(layoutManager) {
+            @Override
+            public void onLoadMore(int page, int totalItemsCount, RecyclerView view) {
+                loadMoreData(totalItemsCount);
+            }
+        };
+        mChatEventsList.addOnScrollListener(mChatScrollListener);
+
         if (getArguments() != null) {
             String fileSharedUri = getArguments().getString("fileSharedUri");
             if (fileSharedUri != null) {
@@ -350,9 +365,9 @@ public class GroupChatFragment extends Fragment implements ChatRoomListener, Con
             eventLog.deleteFromDatabase();
         }
         if (mChatRoom.hasCapability(ChatRoomCapabilities.OneToOne.toInt())) {
-            mEventsAdapter.refresh(mChatRoom.getHistoryMessageEvents(0));
+            mEventsAdapter.refresh(mChatRoom.getHistoryMessageEvents(MESSAGES_PER_PAGE));
         } else {
-            mEventsAdapter.refresh(mChatRoom.getHistoryEvents(0));
+            mEventsAdapter.refresh(mChatRoom.getHistoryEvents(MESSAGES_PER_PAGE));
         }
     }
 
@@ -424,6 +439,24 @@ public class GroupChatFragment extends Fragment implements ChatRoomListener, Con
         return super.onContextItemSelected(item);
     }
 
+    private void loadMoreData(final int totalItemsCount) {
+        mHandler.post(new Runnable() {
+            @Override
+            public void run() {
+                int maxSize = mChatRoom.getHistoryEventsSize();
+                if (totalItemsCount < maxSize) {
+                    int upperBound = totalItemsCount + MESSAGES_PER_PAGE;
+                    if (upperBound > maxSize) {
+                        upperBound = maxSize;
+                    }
+                    EventLog[] newLogs = mChatRoom.getHistoryRangeEvents(totalItemsCount, upperBound);
+                    ArrayList<EventLog> logsList = new ArrayList<>(Arrays.asList(newLogs));
+                    mEventsAdapter.addAllToHistory(logsList);
+                }
+            }
+        });
+    }
+
     /**
      * Keyboard management
      */
@@ -563,9 +596,9 @@ public class GroupChatFragment extends Fragment implements ChatRoomListener, Con
 
         if (mChatRoom == null) return;
         if (mChatRoom.hasCapability(ChatRoomCapabilities.OneToOne.toInt())) {
-            mEventsAdapter = new ChatEventsAdapter(this, mSelectionHelper, R.layout.chat_bubble, mChatRoom.getHistoryMessageEvents(0), mParticipants, this);
+            mEventsAdapter = new ChatEventsAdapter(this, mSelectionHelper, R.layout.chat_bubble, mChatRoom.getHistoryMessageEvents(MESSAGES_PER_PAGE), mParticipants, this);
         } else {
-            mEventsAdapter = new ChatEventsAdapter(this, mSelectionHelper, R.layout.chat_bubble, mChatRoom.getHistoryEvents(0), mParticipants, this);
+            mEventsAdapter = new ChatEventsAdapter(this, mSelectionHelper, R.layout.chat_bubble, mChatRoom.getHistoryEvents(MESSAGES_PER_PAGE), mParticipants, this);
         }
         mSelectionHelper.setAdapter(mEventsAdapter);
         mChatEventsList.setAdapter(mEventsAdapter);
@@ -573,7 +606,7 @@ public class GroupChatFragment extends Fragment implements ChatRoomListener, Con
     }
 
     public void scrollToBottom() {
-        mChatEventsList.getLayoutManager().scrollToPosition(mEventsAdapter.getCount() - 1);
+        mChatEventsList.getLayoutManager().scrollToPosition(0);
     }
 
     public String getRemoteSipUri() {