Package org.eclipse.gmf.runtime.common.core.service
Provides the base interfaces for all service providers.
See:
Description
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Interface Summary
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IOperation
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The interface for all service provider operations. |
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IProvider
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The interface for all service providers. |
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IProviderChangeListener
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An interface for types that listen to service provider changes. |
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IProviderPolicy
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The interface for all service providers lightweight's implementation. |
Package org.eclipse.gmf.runtime.common.core.service Description
Provides the base interfaces for all service providers. The following examples are some of the services in the modeling platform:
- Layout Service
- Property Service
- Decorator Service
The modeling platform consists of a set of services whose requests are fulfilled by service providers that implement
IProvider.
Each service exposes an extension-point that providers extend to be discovered and used. This package contains classes that define the abstract contract for service providers.
Package Specification
When it receives a client request, a service typically embeds the request information in an
IOperation and then evaluates the
extensions of its defined extension-point to find potential providers for the request. To determine to which providers to delegate a request,
a service uses two sequential filters:
- The service evaluates the information in each provider's extension descriptor. The service extension-point schema typically filters
out most providers in this step and prevents the unnecessary loading of a provider.
- The service requests information from each provider about whether it can support the request. The provider's
IProvider.provides implementation performs this action.
Typically, the service sorts the providers that passed the filters according to the priority that the service provider extension descriptor defines.
Depending on the service and the request, the service might request one or more providers to perform the operation. After the required providers are defined, the service
delegates the execution of the request for each provider to the operation's
IOperation.execute implementation.
Each service provides its own IOperation subclass that subsequently delegates to the provider.
Most services expose an abstract class implementing IProvider that providers should subclass. The abstract class specifies the contract between the service and its providers since
it specifies the API to perform requests. The abstract class usually extends
AbstractProvider to leverage the notification support of this class.
Some services require notification from a provider if the provider's state changes. This notification occurs through the
IProviderChangeListener interface. These types of service connect to their provider using
addProviderChangeListener and disconnect using
removeProviderChangeListener. Services often
provide their own derived
ProviderChangeEvent classes to convey more
service-specific information about the state change.
Sometimes, it is impossible to provide enough information in a service provider extension descriptor to avoid
the unnecessary loading of the provider plug-in. When the cost of loading a provider plug-in is high, it might be preferable to move
the implementation of
IProvider.provides to a lightweight plug-in.
To do this, a service provider extension descriptor should include a "Policy" subelement with
a class attribute that references a class that implements
IProviderPolicy. This
interface is a subset of IProvider that only includes the
IProviderPolicy.provides member.
Guidelines for using Eclipse APIs.
Copyright (c) IBM Corp., Borland Software Corp., and others 2005,2006. All rights reserved.
