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    <p>There are many different ways to attack this. I don't disagree with the other answers posted here.</p> <p>However, one way that I've done this is by using the observer pattern. And let me explain why.</p> <p>The observer pattern is necessary here because these drawing tools are nothing without the canvas. So, if you have no canvas, you can't (or shouldn't) invoke the circle tool. So instead, my canvas has a host of observers on it.</p> <p>Each tool that can be used on the canvas is added as an observable event. Then, when an event is fired - like "begin draw" - the tool is sent as the context (in this case 'circle'). From there, the actions of the circle tool execute. </p> <p>Another way to imagine this is that each layer has its own service, model, and view. The controller really is at the exterior level and associated with the canvas. So, services are only called by other services or by a controller. There are no circle tool controllers - so only another service (in our case the observed event) can call it. That service is responsible for aggregating the data, building the model, and supplying a view.</p>
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    1. PONested MVC communication patterns
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    1. USAaron Saray
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      1. VTUpMod
    1. COThe way I have the tools currently set up is pretty similar to that actually. The CanvasController has an 'activeTool', that implements an interface containing methods like 'onClick', 'onMouseMove', etc... and on such events the active tool's methods are called. The part I'm struggling with is how the tool services add new drawn entities. Since the each part of the Canvas MVC triad has it's own collection of entities (e.g. CanvasController has a list of WidgetControllers, CanvasView has a list of WidgetViews). Does the tool service create all 3 of the widget MVC classes and add them?
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      1. USchinabuffet
    2. COI'm not entirely certain if I follow the question... but let me see. I would think the best result on this is that the 'active tool' is actually the service for that tool. You can strip down some of the MVC in this case. There is no need for a controller here - because the service already has those methods ( from the interface ) that you described. Your canvas controller is already calling them, so there should be no "child" controller. As for the associated view, I've never been too sure - I generally invoke the "magical" (heh) "helper class" which automagically interprets view creation.
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    3. COI updated my original question to include a pseudo-codish example. The CircleTool doesn't have it's own completely separate MVC if that's what you were referring to. I may end up just using some kind of "magical" helper class haha... Hoping to find some kind of approach that feels better though.
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