1# Protocol Buffers - Google's data interchange format 2# Copyright 2008 Google Inc. All rights reserved. 3# https://developers.google.com/protocol-buffers/ 4# 5# Redistribution and use in source and binary forms, with or without 6# modification, are permitted provided that the following conditions are 7# met: 8# 9# * Redistributions of source code must retain the above copyright 10# notice, this list of conditions and the following disclaimer. 11# * Redistributions in binary form must reproduce the above 12# copyright notice, this list of conditions and the following disclaimer 13# in the documentation and/or other materials provided with the 14# distribution. 15# * Neither the name of Google Inc. nor the names of its 16# contributors may be used to endorse or promote products derived from 17# this software without specific prior written permission. 18# 19# THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS 20# "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT 21# LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR 22# A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT 23# OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, 24# SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT 25# LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, 26# DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY 27# THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT 28# (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE 29# OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. 30 31"""Defines a listener interface for observing certain 32state transitions on Message objects. 33 34Also defines a null implementation of this interface. 35""" 36 37__author__ = 'robinson@google.com (Will Robinson)' 38 39 40class MessageListener(object): 41 42 """Listens for modifications made to a message. Meant to be registered via 43 Message._SetListener(). 44 45 Attributes: 46 dirty: If True, then calling Modified() would be a no-op. This can be 47 used to avoid these calls entirely in the common case. 48 """ 49 50 def Modified(self): 51 """Called every time the message is modified in such a way that the parent 52 message may need to be updated. This currently means either: 53 (a) The message was modified for the first time, so the parent message 54 should henceforth mark the message as present. 55 (b) The message's cached byte size became dirty -- i.e. the message was 56 modified for the first time after a previous call to ByteSize(). 57 Therefore the parent should also mark its byte size as dirty. 58 Note that (a) implies (b), since new objects start out with a client cached 59 size (zero). However, we document (a) explicitly because it is important. 60 61 Modified() will *only* be called in response to one of these two events -- 62 not every time the sub-message is modified. 63 64 Note that if the listener's |dirty| attribute is true, then calling 65 Modified at the moment would be a no-op, so it can be skipped. Performance- 66 sensitive callers should check this attribute directly before calling since 67 it will be true most of the time. 68 """ 69 70 raise NotImplementedError 71 72 73class NullMessageListener(object): 74 75 """No-op MessageListener implementation.""" 76 77 def Modified(self): 78 pass 79