While trying to understand UIEvents and how the topics are built up for
subscribe operations I found the buildTopic() methods a little cumbersome
and a barrier to understanding what was really going on.
I would like to make a suggestion that I think would
1) Make the code look cleaner
2) Make the concepts clearer
3) Improve run time performance (albeit marginally)
For illustration purposes, here is an example of an interface definition
from UIEvents for the UIElement model object generated by GenTopic
public static interface UIElement {
public static final String TOPIC = UIModelTopicBase +
"/ui/UIElement"; //$NON-NLS-1$
public static final String ACCESSIBILITYPHRASE =
"accessibilityPhrase"; //$NON-NLS-1$
public static final String CONTAINERDATA = "containerData"
; //$NON-NLS-1$
public static final String CURSHAREDREF = "curSharedRef";
//$NON-NLS-1$
public static final String ONTOP = "onTop"; //$NON-NLS-1$
public static final String PARENT = "parent";
//$NON-NLS-1$
public static final String RENDERER = "renderer";
//$NON-NLS-1$
public static final String TOBERENDERED = "toBeRendered";
//$NON-NLS-1$
public static final String VISIBLE = "visible";
//$NON-NLS-1$
public static final String VISIBLEWHEN = "visibleWhen";
//$NON-NLS-1$
public static final String WIDGET = "widget";
//$NON-NLS-1$
}
To subscribe to an event that tracks a UIElements visible change you would
write
eventBroker.subscribe(UIEvents.buildTopic(UIEvents.UIElement.TOPIC,
UIEvents.UIElement.VISIBLE), visibilityHandler);
To subscribe to all changes to UIElement you would write
eventBroker.subscribe(UIEvents.buildTopic(UIEvents.UIElement.TOPIC),
visibilityHandler);
I think it would be much nicer to write, for the first case,
eventBroker.subscribe(UIEvents.UIElement.VISIBLE), visibilityHandler);
or, for the second case,
eventBroker.subscribe(UIEvents.UIElement.ALL), visibilityHandler);
To make this possible I propose that we would generate the UIElement
interface definition like this.
public static interface UIElement {
public static final String ALL= UIModelTopicBase +
"/ui/UIElement/*"; //$NON-NLS-1$
public static final String VISIBLE = UIModelTopicBase +
"/ui/UIElement/" + "visible"; //$NON-NLS-1$
...
}
This would allow us to delete two of the buildTopic() methods. We could
leave the 3 argument version of buildTopic() to retain construction of
topics that filter based on event type ( although nobody calls this
internally at this time so do we really need it?).
The code would also be more efficient as we would be removing method calls
that do string concatenation with simple static references. In fact, I
believe the compiler will just in line the references at compile time.
Although I would be a fan of simply making these changes and requiring
consumers to make a few small simplifying changes, we could provide a
stepping stone by regenerating the new shape, deprecating the buildTopic()
methods and all the TOPIC fields. We would then change the implementation
of the buildTopic methods to return the appropriate constant directly
without concatenating.
Admittedly there is higher priority work to be done but since this class
is essentially API, if we don't change it now, we will never be able to
make the change. And I think the clarity in the subscribe statements make
the change worth it. This change seems to fit well with the Eclipse 4
mantra that simple things should be simple.
I also believe the effort required to change GenTopic to generate the new
shape is small, and I volunteer to create the patch. Admittedly changing
the calling code to use the new shape is more wide spread, but a very
simple task. Although an actual committer probably wants to do that work
as it would be a LOT of patches to apply :-)
What does the community think? Does it make sense? Am I totally off
base?
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