index.md

Advanced MVC

Event bus / PubSub

Example, wxpython provides a nice example of pubsub model

.. code::

import wx
from wx.lib.pubsub import Publisher

class Model:
    def __init__(self):
        self.myMoney = 0

    def addMoney(self, value):
        self.myMoney += value
        Publisher.sendMessage("MONEY CHANGED", self.myMoney)

The controller can now subscribe to the qualified notification as follows. The handler will receive a message, qualified with the appropriate information

.. code::

class Controller:
    def __init__(self, app):
        # <...>
        pub.subscribe(self.moneyChangedHandler, "MONEY CHANGED")

    def moneyChangedHandler(self, message):
        """
        This method is the handler for "MONEY CHANGED" messages,
        which pubsub will call as messages are sent from the model.

        We already know the topic is "MONEY CHANGED", but if we
        didn't, message.topic would tell us.
        """
        self.view.setMoney(message.data)

An additional flexibility of this mechanism, compared to the pubsub mechanism proposed earlier, is that messages can now be spooled, packed, and delivered asynchronously, if the need emerges.

For example, a message producer occasionally producing bursts of changes could put the notification in a spool. When the spool delivers the messages it can verify that actually multiple notations have been performed within a small amount of time, and simply deliver to the listener only one message, removing trashing caused by excessive refresh requests.

Model distribution

Scriptability Modification of the model programmatically can enable scripting