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 Set TOPICTITLE = The extension registry
 
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The extension registry

<-- 

 Set ALLOWTOPICCHANGE = RegisteredUsersGroup, TWikiAdminGroup
 
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• Set INIT_PY = __init__.py

• Set FINE_TIME = Hcss.FineTime

<--
   Some short-cuts 

 Set VIEWABLE   = Viewable
 
 Set VIEWPART   = ViewPart
 
 Set JCOMPONENT = javax.swing.JComponent
 
 Set REGISTRY   = Extension Registry
 
 Set INIT_PY    = __init__.py
 
 Set SELISTENER = SiteEventListener
 
 

 Set EXTENSION_REGISTRY= ExtensionRegistry
 
 Set EXTENSION         = Extension
 
 Set VARIABLES_VIEW    = VariablesView
 
 Set OUTLINE_VIEW      = OutlineView
 
 Set OUTLINE_COMPONENT = OutlineComponent
 
 Set EDITOR_COMPONENT  = EditorComponent
 
 Set SELECTION_EVENT   = SelectionEvent
 
 Set FINE_TIME         = FineTime
 
 Set EXPLORER          = Explorer
 
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The Extension Registry

<-- summary -->

This section explains the workings of the registry works and how it can automatically find your contribution.

Introduction

The registry mechanism relies on the recursive reading of the jython package modules built into the HCSS. The application will execute the following line:

from herschel.all import *

That line will read sub-packages (share,==ia==,==spire==,==hifi==,==pacs==) which read their sub-packages and so forth. At some point the __init__.py of your sub-system is read. This of course only works if the relevant __init__.py and optionally the all.py files are provided in these packages. Discussion of the workings of these files fall outside the scope of this document.

The idea is that in such a file you call the ExtensionRegistry singleton and add your contribution to it as follows:

ExtensionRegistry.getInstance().register(CLASSIFICATION, Extension(....))

where CLASSIFICATION is one of (pre-defined):

• ExtensionRegistry.COMPONENT adds a new component to some factory
• ExtensionRegistry.FACTORY adds a new factory
• ExtensionRegistry.VIEW adds a new view
• ExtensionRegistry.PERSPECTIVE adds a new perspective

or a new type if you deem it necessary.

To keep the code readable, we recommend you to use temporary aliases, which you should clean-up afterwards:

# short-cuts
from herschel.ia.core import ExtensionRegistry, Extension
REGISTRY=ExtensionRegistry.getInstance()
COMPONENT=ExtensionRegistry.COMPONENT

# registry
REGISTRY.register(COMPONENT,Extension(...))
REGISTRY.register(COMPONENT,Extension(...))
REGISTRY.register(COMPONENT,Extension(...))
REGISTRY.register(COMPONENT,Extension(...))
REGISTRY.register(COMPONENT,Extension(...))
REGISTRY.register(COMPONENT,Extension(...))

# clean-up
del(ExtensionRegistry, Extension, REGISTRY, COMPONENT)

The registry mechanism is made loosely in such way that it does not matter in which order the packages are read (and therefor the extensions are being added). At run-time all extensions are read first; once done it starts interpreting the contents of the registry.

Extension API

The Extension class is a very simple class with a constructor that takes String arguments (TODO expand it):

Extension(id,class, arg1, arg2)

where:

• id is a unique ID for this extension
• class is the java class definition

The meaning of arg1 and arg2 varies depending on the classification of the extension.

Perspective Extension

arg1	Human readable title of the perspective as it should appear in the menu, e.g. "Hello World"
arg2	Resource location of a 16x16 Icon for this perspective, e.g. "herschel/spire/icon/hello.gif" or None

An example for the JIDE perspective:

Extension("site.perspective.classic",
          "herschel.ia.gui.perspectives.ClassicPerspective",
          "Classic (JIDE)",
          None)

View Extension

arg1	Human readable title of the view as it should appear in the menu and in the title bar of the view, e.g. "Hello World"
arg2	Resource location of a 16x16 Icon for this view, e.g. "herschel/spire/icon/hello.gif" or None

An example for the Console View:

Extension("site.view.console",
          "herschel.ia.gui.views.ConsoleView",
          "Console",
          "herschel/ia/core/icons/Console.gif")

Factory Extension

If views are using extendable factories, the API of that view should provide sufficient information about how to add factories. Typically views use factories whenever that view needs to react on a user selection, for example a user selects a variable and that view should show something about that variable. In that case the variable selection is coupled to a factory in that specific view such that other contributors can contribute a component for new types of variables.

An example is the Outline View. It currently can respond to selections of variables, but it could respond to other types of selections such as tools. For that it has uses factories for which applies:

arg1	Specifies the type (class definition) of the selection
arg2	Specifies the unique ID of the view that this factory belongs to

For variable selections, a factory is defined:

Extension("factory.outline.variable",
          "herschel.ia.core.VariableSelectionFactory",
          "herschel.ia.core.VariableSelection",
          "site.view.outline")

Component Extension

Contributors can add components to existing factories. Taking the example of the "factory.outline.variable" factory that coupled to the Outline View, the syntax of an extension becomes as follows:

arg1	Specifies the unique ID of the factory to which this component belongs to
arg2	Specifies class definition of the object that this component can show

An example of such a component:

Extension("herschel.ia.gui.components.outline.ProductOutline",
          "herschel.ia.gui.components.outline.ProductOutline",
          "factory.outline.variable",
          "herschel.ia.dataset.Product")

It is a component that shows structure of a Product within the Outline View.

<-- Author: JorgoBakker -->