/**
     * 功能：本地内容同步操作
     * @throws NetworkFailureException
     * @return 无返回值
     */
    private void syncContent() throws NetworkFailureException {    //本地内容同步操作
        int syncType;
        Cursor c = null;                                           //数据库指针
        String gid;                                                //GoogleID
        Node node;                                                 //Node包含Sync_Action的不同类型
 
        mLocalDeleteIdMap.clear();                                 //HashSet<Long>类型
 
        if (mCancelled) {
            return;
        }
 
        // for local deleted note
        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)
                    }, null);
            if (c != null) {
                while (c.moveToNext()) {
                    gid = c.getString(SqlNote.GTASK_ID_COLUMN);
                    node = mGTaskHashMap.get(gid);
                    if (node != null) {
                        mGTaskHashMap.remove(gid);
                        doContentSync(Node.SYNC_ACTION_DEL_REMOTE, node, c);
                    }
 
                    mLocalDeleteIdMap.add(c.getLong(SqlNote.ID_COLUMN));
                }
            } else {
                Log.w(TAG, "failed to query trash folder");
            }
        } finally {
            if (c != null) {
                c.close();
                c = null;
            }
        }
 
        // sync folder first
        syncFolder();
 
        // for note existing in database
        try {
            c = mContentResolver.query(Notes.CONTENT_NOTE_URI, SqlNote.PROJECTION_NOTE,
                    "(type=? AND parent_id<>?)", new String[] {
                            String.valueOf(Notes.TYPE_NOTE), String.valueOf(Notes.ID_TRASH_FOLER)
                    }, NoteColumns.TYPE + " DESC");
            if (c != null) {
                while (c.moveToNext()) {
                    gid = c.getString(SqlNote.GTASK_ID_COLUMN);
                    node = mGTaskHashMap.get(gid);
                    if (node != null) {
                        mGTaskHashMap.remove(gid);
                        mGidToNid.put(gid, c.getLong(SqlNote.ID_COLUMN));   //通过hashmap建立联系
                        mNidToGid.put(c.getLong(SqlNote.ID_COLUMN), gid);   //通过hashmap建立联系
                        syncType = node.getSyncAction(c);
                    } else {
                        if (c.getString(SqlNote.GTASK_ID_COLUMN).trim().length() == 0) {
                            // local add
                            syncType = Node.SYNC_ACTION_ADD_REMOTE;
                        } else {
                            // remote delete
                            syncType = Node.SYNC_ACTION_DEL_LOCAL;
                        }
                    }
                    doContentSync(syncType, node, c);
                }
            } else {
                Log.w(TAG, "failed to query existing note in database");
            }
 
        } finally {
            if (c != null) {
                c.close();
                c = null;
            }
        }
 
        // go through remaining items
        Iterator<Map.Entry<String, Node>> iter = mGTaskHashMap.entrySet().iterator();   //Iterator迭代器
        while (iter.hasNext()) {
            Map.Entry<String, Node> entry = iter.next();
            node = entry.getValue();
            doContentSync(Node.SYNC_ACTION_ADD_LOCAL, node, null);
        }
 
        // mCancelled can be set by another thread, so we neet to check one by    //thread----线程
        // one
        // clear local delete table
        if (!mCancelled) {
            if (!DataUtils.batchDeleteNotes(mContentResolver, mLocalDeleteIdMap)) {
                throw new ActionFailureException("failed to batch-delete local deleted notes");
            }
        }
 
        // refresh local sync id
        if (!mCancelled) {
            GTaskClient.getInstance().commitUpdate();
            refreshLocalSyncId();
        }
 
    }