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<H3><A NAME="SECTION000293000000000000000">
2.9.3 Propagating changes from Model to Proxy</A>
</H3>
<P>
In our previous example, our model was defined as an instance of a
simple Python class. If we use the complete framework, by having our
model classes inherit from <tt class="class">FrameWork.Model</tt>, we also get reverse
notifications from Model to Proxy: when the model is altered, the change
propagates to the proxy interface attached to it.
<P>
To demonstrate, we can extend the example above to add a "reset" button
to trigger a change of the model; we will subclass ProxyDelegate (which is
also a Delegate, as stated before, and thus supports the special handler
syntax <code>on_*()</code>) to define a handler for clicking on the reset
button (<span class="file">examples/framework/newsform/newsform2.py</span>):
<P>
If we look at the handler for reset, <code>on_reset__clicked()</code>, we
can see it alters the model directly. These changes reflect
automatically in the interface by means of an update mechanism present
in <tt class="class">FrameWork.Model</tt>. This holds true no matter what function
triggers the change in the model: it is not limited to callbacks defined
in Proxy itself; any handler that alters the model will trigger the
model's update mechanism.
<P>
In summary: if you need to alter your model independently of the
interface, have your model inherit from FrameWork.Model and enjoy
automatic UI updating.
<P>
In all the examples we have shown up to now, you may notice that the
proxy manipulates the model's instance variables directly. There are
times where this is not desirable, and the next section explains how to
customize the proxy and model's behavior.
<P>
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<span class="release-info">Release 1.9.22, documentation updated on August, 2006.</span>
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