Improve scroll to last position behavior.

app/src/main/java/org/thoughtcrime/securesms/conversation/ConversationFragment.java

@@ -287,7 +287,7 @@ public class ConversationFragment extends LoggingFragment {
     int firstVisiblePosition = getListLayoutManager().findFirstCompletelyVisibleItemPosition();
 
     final long lastVisibleMessageTimestamp;
-    if (firstVisiblePosition != 0 && lastVisiblePosition != RecyclerView.NO_POSITION) {
+    if (firstVisiblePosition > 0 && lastVisiblePosition != RecyclerView.NO_POSITION) {
       MessageRecord message = getListAdapter().getLastVisibleMessageRecord(lastVisiblePosition);
 
       lastVisibleMessageTimestamp = message != null ? message.getDateReceived() : 0;

app/src/main/java/org/thoughtcrime/securesms/database/ThreadDatabase.java

@@ -51,7 +51,6 @@ import org.thoughtcrime.securesms.util.CursorUtil;
 import org.thoughtcrime.securesms.util.JsonUtils;
 import org.thoughtcrime.securesms.util.TextSecurePreferences;
 import org.thoughtcrime.securesms.util.Util;
-import org.whispersystems.libsignal.util.Pair;
 import org.whispersystems.libsignal.util.guava.Optional;
 import org.whispersystems.signalservice.api.groupsv2.DecryptedGroupUtil;
 
@@ -193,6 +192,10 @@ public class ThreadDatabase extends Database {
       contentValues.put(ARCHIVED, 0);
     }
 
+    if (count != getConversationMessageCount(threadId)) {
+      contentValues.put(LAST_SCROLLED, 0);
+    }
+
     SQLiteDatabase db = databaseHelper.getWritableDatabase();
     db.update(TABLE_NAME, contentValues, ID + " = ?", new String[] {threadId + ""});
     notifyConversationListListeners();
@@ -666,6 +669,17 @@ public class ThreadDatabase extends Database {
     }
   }
 
+  public int getConversationMessageCount(long threadId) {
+    SQLiteDatabase db = databaseHelper.getReadableDatabase();
+
+    try (Cursor cursor = db.query(TABLE_NAME, new String[]{MESSAGE_COUNT}, ID_WHERE, new String[]{String.valueOf(threadId)}, null, null, null)) {
+      if (cursor != null && cursor.moveToFirst()) {
+        return CursorUtil.requireInt(cursor, MESSAGE_COUNT);
+      }
+    }
+    return 0;
+  }
+
   public void deleteConversation(long threadId) {
     DatabaseFactory.getSmsDatabase(context).deleteThread(threadId);
     DatabaseFactory.getMmsDatabase(context).deleteThread(threadId);