/**
     * 功能：更新远端的Node，包含meta更新(updateRemoteMeta)
     * @author TTS
     * @param node
     * ----同步操作的基础数据类型
     * @param c
     *  --Cursor
     * @throws NetworkFailureException
     */
    private void updateRemoteNode(Node node, Cursor c) throws NetworkFailureException {
        if (mCancelled) {
            return;
        }
 
        SqlNote sqlNote = new SqlNote(mContext, c);
 
        // update remotely
        node.setContentByLocalJSON(sqlNote.getContent());
        GTaskClient.getInstance().addUpdateNode(node);                                //GTaskClient用途为从本地登陆远端服务器 
 
        // update meta
        updateRemoteMeta(node.getGid(), sqlNote);
 
        // move task if necessary
        if (sqlNote.isNoteType()) {
            Task task = (Task) node;
            TaskList preParentList = task.getParent(); 
            //preParentList为通过node获取的父节点列表
            
            String curParentGid = mNidToGid.get(sqlNote.getParentId());
            //curParentGid为通过光标在数据库中找到sqlNote的mParentId，再通过mNidToGid由long类型转为String类型的Gid
            
            if (curParentGid == null) {
                Log.e(TAG, "cannot find task's parent tasklist");
                throw new ActionFailureException("cannot update remote task");
            }
            TaskList curParentList = mGTaskListHashMap.get(curParentGid);
            //通过HashMap找到对应Gid的TaskList
 
            if (preParentList != curParentList) {                                          //?????????????
                preParentList.removeChildTask(task);
                curParentList.addChildTask(task);
                GTaskClient.getInstance().moveTask(task, preParentList, curParentList);
            }
        }
 
        // clear local modified flag
        sqlNote.resetLocalModified();
        //commit到本地数据库
        sqlNote.commit(true); 
    }
 
    /**
     * 功能：升级远程meta。  meta---元数据----计算机文件系统管理数据---管理数据的数据。
     * @author TTS
     * @param gid
     * ---GoogleID为String类型
     * @param sqlNote
     * ---同步前的数据库操作，故使用类SqlNote
     * @throws NetworkFailureException
     */
    private void updateRemoteMeta(String gid, SqlNote sqlNote) throws NetworkFailureException {
        if (sqlNote != null && sqlNote.isNoteType()) {
            MetaData metaData = mMetaHashMap.get(gid);
            if (metaData != null) {
                metaData.setMeta(gid, sqlNote.getContent());
                GTaskClient.getInstance().addUpdateNode(metaData);
            } else {
                metaData = new MetaData();
                metaData.setMeta(gid, sqlNote.getContent());
                mMetaList.addChildTask(metaData);
                mMetaHashMap.put(gid, metaData);
                GTaskClient.getInstance().createTask(metaData);
            }
        }
    }
 
    /**
     * 功能：刷新本地，给sync的ID对应上最后更改过的对象
     * @author TTS
     * @return void
     * @throws NetworkFailureException
     */
    private void refreshLocalSyncId() throws NetworkFailureException {
        if (mCancelled) {
            return;
        }
 
        // get the latest gtask list                                               //获取最近的（最晚的）gtask list
        mGTaskHashMap.clear();
        mGTaskListHashMap.clear();
        mMetaHashMap.clear();
        initGTaskList();
 
        Cursor c = null;
        try {
            c = mContentResolver.query(Notes.CONTENT_NOTE_URI, SqlNote.PROJECTION_NOTE,
                    "(type<>? AND parent_id<>?)", new String[] {
                            String.valueOf(Notes.TYPE_SYSTEM), String.valueOf(Notes.ID_TRASH_FOLER)
                    }, NoteColumns.TYPE + " DESC");                                                 //query语句：五个参数，NoteColumns.TYPE + " DESC"-----为按类型递减顺序返回查询结果。new String[] {String.valueOf(Notes.TYPE_SYSTEM), String.valueOf(Notes.ID_TRASH_FOLER)}------为选择参数。"(type<>? AND parent_id<>?)"-------指明返回行过滤器。SqlNote.PROJECTION_NOTE--------应返回的数据列的名字。Notes.CONTENT_NOTE_URI--------contentProvider包含所有数据集所对应的uri
            if (c != null) {
                while (c.moveToNext()) {
                    String gid = c.getString(SqlNote.GTASK_ID_COLUMN);
                    Node node = mGTaskHashMap.get(gid);
                    if (node != null) {
                        mGTaskHashMap.remove(gid);
                        ContentValues values = new ContentValues();                     //在ContentValues中创建键值对。准备通过contentResolver写入数据
                        values.put(NoteColumns.SYNC_ID, node.getLastModified());
                        mContentResolver.update(ContentUris.withAppendedId(Notes.CONTENT_NOTE_URI,   //进行批量更改，选择参数为NULL，应该可以用insert替换，参数分别为表名和需要更新的value对象。
                                c.getLong(SqlNote.ID_COLUMN)), values, null, null);
                    } else {
                        Log.e(TAG, "something is missed");
                        throw new ActionFailureException(
                                "some local items don't have gid after sync");
                    }
                }
            } else {
                Log.w(TAG, "failed to query local note to refresh sync id");
            }
        } finally {
            if (c != null) {
                c.close();
                c = null;
            }
        }
    }
 
    /**
     * 功能：获取同步账号,mAccount.name
     * @author TTS
     * @return String
     */
    public String getSyncAccount() {
        return GTaskClient.getInstance().getSyncAccount().name;
    }
 
    /**
     * 功能：取消同步，置mCancelled为true
     * @author TTS
     */
    public void cancelSync() {
        mCancelled = true;
    }
}