| # Protocol Buffers - Google's data interchange format |
| # Copyright 2008 Google Inc. All rights reserved. |
| # http://code.google.com/p/protobuf/ |
| # |
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| |
| """Defines a listener interface for observing certain |
| state transitions on Message objects. |
| |
| Also defines a null implementation of this interface. |
| """ |
| |
| __author__ = 'robinson@google.com (Will Robinson)' |
| |
| |
| class MessageListener(object): |
| |
| """Listens for modifications made to a message. Meant to be registered via |
| Message._SetListener(). |
| |
| Attributes: |
| dirty: If True, then calling Modified() would be a no-op. This can be |
| used to avoid these calls entirely in the common case. |
| """ |
| |
| def Modified(self): |
| """Called every time the message is modified in such a way that the parent |
| message may need to be updated. This currently means either: |
| (a) The message was modified for the first time, so the parent message |
| should henceforth mark the message as present. |
| (b) The message's cached byte size became dirty -- i.e. the message was |
| modified for the first time after a previous call to ByteSize(). |
| Therefore the parent should also mark its byte size as dirty. |
| Note that (a) implies (b), since new objects start out with a client cached |
| size (zero). However, we document (a) explicitly because it is important. |
| |
| Modified() will *only* be called in response to one of these two events -- |
| not every time the sub-message is modified. |
| |
| Note that if the listener's |dirty| attribute is true, then calling |
| Modified at the moment would be a no-op, so it can be skipped. Performance- |
| sensitive callers should check this attribute directly before calling since |
| it will be true most of the time. |
| """ |
| |
| raise NotImplementedError |
| |
| |
| class NullMessageListener(object): |
| |
| """No-op MessageListener implementation.""" |
| |
| def Modified(self): |
| pass |