Difference between revisions of "Plug-in pattern"

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:The ''host'' of the ''plug-in''.
 
:The ''host'' of the ''plug-in''.
 
;Site
 
;Site
:The ''plug-in'' explose data and functionality to the ''host'', but the ''plug-in'' may also need to draw upon data and services from the ''host''.  The ''site'' represent the ''plug-in'''s ''host'' access.
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:The ''plug-in'' expose data and functionality to the ''host'', but the ''plug-in'' may also need to draw upon data and services from the ''host''.  The ''site'' represent the ''plug-in'''s ''host'' access.
  
 
There are two contracts in the pattern:
 
There are two contracts in the pattern:

Latest revision as of 16:35, 12 February 2015

The plug-in pattern is a design pattern. I believe it is widely used, but I have not seen it described anywhere, and plug-in pattern is the name I have given it.

The pattern have three actors:

Plug-in
The plug-in (sometimes called the client), which is plugged into the host.
Host
The host of the plug-in.
Site
The plug-in expose data and functionality to the host, but the plug-in may also need to draw upon data and services from the host. The site represent the plug-in's host access.

There are two contracts in the pattern:

  • The plug-in interface, which defines the hosts view of the plug-in
  • The site interface, which defines the plug-in's view of the host

PFC has many of uses the Support pattern, which is a specialization of the plug-in pattern.

Example

A SAPI (i.e. Speech API) speech recognizer engine is a plug-in hosted by the Windows SAPI system.

The engine is the plug-in and Windows SAPI is the host. The plug-in must implement the interface ISpSREngine, which is the host's view of the engine.

The host will call the function ISpSREngine::SetSite with an object of type ISpSREngineSite. This object is the site object and gives the plug-in access to data and functionality in the host.

In the recognition process the host will feed audio buffers; notify grammar loads and unloads; etc through the ISpSREngine interface. On the other hand, the plug-in will return recognition results; interrogate about grammar details; etc. through the site (ISpSREngineSite) object.