Difference between revisions of "Slicer3:EventBroker"

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(New page: == Currently === The basic idea of the EventBroker is that currently we have a lot of this kind of code in GUIs: node->AddObserver(vtkCommand::ModifiedEvent, callbackCommand) == Problem...)
 
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== Currently ===
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<big>'''Note:''' We are migrating this content to the slicer.org domain - <font color="orange">The newer page is [https://www.slicer.org/wiki/Slicer3:EventBroker  here]</font></big>
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The basic idea of the EventBroker is that currently we have a lot of this kind of code in GUIs:
 
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node->AddObserver(vtkCommand::ModifiedEvent, callbackCommand)
 
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== Problems ==
 
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The problems with this:
 
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* node 'owns' the observer, but the callbackCommand is opaque so it doesn't know anything about what will happen when the event is invoked
 
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* the GUI needs to explicitly remove the observer before it is destroyed
 
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* node is not introspectable; you cannot get a list of observers on the node
 
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* there's no easy way to know what side effects will happen for any Set call (either a priori or experimentally).
 
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* there's no way to collapse events or disable them
 
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== Goals for Solution ==
 
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So the EventBroker would be a singleton, perhaps owned by the ApplicationLogic that would look something like:
 
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  broker->RegisterObserver(node, vtkCommand::ModifiedEvent, this, callbackCommand);
 
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The broker would do the following:
 
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* add DeleteEvent observers to both node and this so it can remove the observer automatically if either side is destroyed
 
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* keep an introspectable list of all observers it knows about
 
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* have an option to keep a log of all event invocations for debugging and performance analysis
 
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* have an option to turn off all event invocations
 
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* have an option to queue all event invocations and invoke them later
 
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* have methods to collapse redundant events in the queue
 
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* perhaps have method to pass event invocations from a processing thread to the main GUI thread?
 

Latest revision as of 17:15, 10 July 2017

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Note: We are migrating this content to the slicer.org domain - The newer page is here

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