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https://issues.apache.org/jira/browse/OFBIZ-3774?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Adrian Crum updated OFBIZ-3774:
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Attachment: OFBIZ-3774.patch
The attached patch is a beginning step - it has the visitor interface for the
screen sub-widgets, and it adds the necessary accept method to the sub-widgets.
There is no interface implementation.
The screen widget model classes already use a pattern similar to visitor called
double dispatch. Essentially, the ScreenStringRenderer implementation calls the
renderWidgetString method of each widget, and that widget method calls the
renderXxxx method in the ScreenStringRenderer. With the visitor pattern, the
renderWidgetString method is called accept, and the renderXxxx method is called
visit. So, it's basically the same design but with a slight difference.
In the current code, the visitor (ScreenStringRenderer) passes a number of
arguments to the model widget renderWidgetString method. In the attached patch,
the visitor (ScreenWidgetVisitor) passes only itself as an argument to the
model widget accept method. The reason for this difference is flexibility and
expandability. Set up this way, the visitor could be anything - a renderer, an
artifact info gatherer, a pretty printer, etc. There is no implementation
implied in the design.
Each renderer would implement ScreenWidgetVisitor. The code inside each model
widget renderWidgetString method would be moved to the corresponding visit
method in the renderer. Likewise, the artifact-info-gatherer would implement
ScreenWidgetVisitor. The existing model widget artifact-info-gathering code
would be moved to the corresponding visit method in the artifact-info-gatherer.
Once those changes are made, the model widgets will contain only object
construction code. Even that code could be moved to a builder class that
implements ScreenWidgetVisitor.
The benefit of this change will be improved separation of concerns. Right now
the screen widget model classes try to be everything to everybody. After the
change they will be little more than data structures that various
behavior-specific objects will refer to. Rendering code is not mixed in with
object construction code or with artifact-gathering code. The API is simplified.
A change like this could have serious downstream consequences for OFBiz users
who have modified the screen widget model classes. One approach we could take
is to put the visit methods in ScreenStringRenderer (instead of having a
separate interface) and then deprecate the existing renderXxxx methods. The
downside is code maintainance - bug fixes and new features will have to be
applied to both patterns.
If you believe the change is worthwhile, then please vote on this issue.
> Add The Visitor Pattern To Screen Widget Model Classes
> ------------------------------------------------------
>
> Key: OFBIZ-3774
> URL: https://issues.apache.org/jira/browse/OFBIZ-3774
> Project: OFBiz
> Issue Type: Improvement
> Components: framework
> Reporter: Adrian Crum
> Priority: Minor
> Attachments: OFBIZ-3774.patch
>
>
> From time to time there has been interest expressed in introducing the
> visitor pattern to the screen widget model classes. This issue is intended to
> provide a forum on the subject and a means to vote on it. Details are in the
> comments.
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