GeoSelectionService.

What is this?

GeoSelectionService is an UDIG object service for geographical information selection management and interoperability of various application parts through unified processing unit.

In Eclipse RCP applications the standard workbench selection service is available for providers and listeners to bind each other through well defined API hiding implementation specifics. The workbench selection service is general and especially used in structured viewers to organize user selections and listeners responsible for the selection processing. It is not fully appropriate for management of selection of distinct geographical information on the map since does not bring the functionality of multiple selection providers (various modal tools being able to make selections with different semantics) and persistent storage has been made across switching of maps.

GeoSelectionService follows the paradigm of standard workbench selection service and brings mentioned functionality for the persistent management of multiple selections of geographical information/objects on the maps in different contexts.

The architecture

The GeoSelectionService API is contained in package net.refractions.udig.project.geoselection. Like ISelection interface works for workbench selection service keeping selected objects, IGeoSelection gives a value for GeoSelectionService. The one advantage of the IGeoSelection is that it is IAdaptable and implementations can be really specific hiding all details behind IAdaptable interface. Listeners don’t really need to know the real implementation of IGeoSelection in most cases while working with IAdaptable.getAdapter(Class) method to extract selected objects of the type they are interested in.

IGeoSelection is still under design.

GeoSelectionService is a just singleton point of access like Display in SWT world. It contains multiple selection managers implementing IGeoSelectionManager interface. The UDIG platform contains the main selection manager:
PlatformGeoSelectionManager implements IGeoSelectionManager

It is available from GeoSelectionService.getDefault().getPlatformSelectionManager().

The functionality of PlatformGeoSelectionManager is based of the currently active MapEditor with an active IMap object. IGeoSelections can be made as by modal tools like standard selection tools or programmatically from any piece of code.

The paradigm of GeoSelectionService brings the next items:
Multiple IGeoSelectionManagers can be registered with GeoSelectionService to serve specific needs of the developers. The default IGeoSelectionManager is an implementation PlatformGeoSelectionManager available from GeoSelectionService.getDefault().getPlatformSelectionManager().
IGeoSelectionManager supports multiple IGeoSelections: each of them in the specified context. The context defines the domain of substitution policy for the IGeoSelection. The substitution policy determines the scope where only one IGeoSelection can be made and be active and persistent. The IGeoSelection being made in a context “rewrites� the previous IGeoSelection in the same .
IGeoSelectionManager supports notification of all registered listeners when any new IGeoSelection is being made with a GeoSelectionChangedEvent.
IGeoSelectionManager supports providing the iteration capability through all currently made and persisted IGeoSelections in their unique contexts.

Use cases

The modal selection tool creates a Filter-based selection of multiple features: IGeoSelection implementation will be adaptable to Filter, ILayer where the selection is made and the object is passed to the PlatformGeoSelectionManager. All listeners will get an event with old selection object, new selection object and other necessary information. Feature editor can listen PlatformGeoSelectionManager to respond on the event: to create an UI for the editing of attributes of multiple features described by Filter.

When the FidFilter is used for one feature the IGeoSelection can adapt to an instance of Feature and a corresponding editor can create an UI for editing of Feature attributes.

The context menu being opened on the MapEditor surface can ask the PlatformGeoSelectionManager and iterate through all currently available IGeoSelections to create necessary items in the menu. For this purpose the new small framework is desired to configure context menu items based on IGeoSelections in GeoSelectionService through RCP extension point mechanism in future.