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LNS Programmer's Guide

281

To accomplish these tasks, the LNS director application must have access to the

Windows Registry, to the LNS Object Server hierarchy, and must implement the client-

side of the LNS plug-in API.

Implementing the Client-Side LNS Plug-In API

The LNS Plug-In API is a simple COM interface that defines a list of properties and

methods by name. The LNS director application can reference an LNS plug-in

application using the plug-in application’s registered server name, and in doing so access

the plug-in application’s methods and properties.

The following code example illustrates how an LNS director application written in Visual

Basic can connect to a plug-in application. The plug-in is identified by its registered

server name. The proper way to retrieve a plug-in application’s server name is discussed

later in this section.

Dim MyPlugIn As Object

Set MyPlugIn = CreateObject(RegisteredServerName)

Note the COM client variable MyPlugIn is declared as Object. It is important that the

LNS director application uses late binding techniques when connecting to plug-in

software. The LNS plug-in API contains the definition of methods and properties by

name, but details no requirements or restrictions for the related DispID identifiers. Each

plug-in will generally use different DispID identifiers when implementing the various

properties and methods detailed in the LNS Plug-In API.

Once the director application has attached to the plug-in, the director can access the

plug-in application’s properties and methods by name. LNS plug-in applications launch

in their hidden state, allowing important properties to be set by the director. The director

will then typically make the plug-in visible by writing to its Visible property, as shown

in the following example:

Dim MyPlugIn As Object

‘ connect to the plug-in

Set MyPlugIn = CreateObject(RegisteredServerName)

SetFocus

‘ insert code to pre-set the plug-in as needed

‘ ...

‘ make plug-in visible:

MyPlugIn.Visible = true

Note that the director application also calls SetFocus after connecting to the plug-in.

Some plug-ins may take the focus away from the director when being launched, leaving

the director’s dialog defocused. Subject to details of the director’s implementation, it may

be a good idea to reclaim the focus in the interest of an uninterrupted user experience.

The plug-in manages its own lifetime independently, so the director need not terminate

the plug-in or reset it to the invisible (hidden) state. However, the director should release

its reference to the plug-in when it will not be needed in the foreseeable future, as shown

here:

Set MyPlugIn = nothing

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