Defining Function Contexts And Tasks; Including Scripts With Require() - Adobe 65007312 - Photoshop Lightroom Programmer's Manual

C 1: Using the Lightroom SDK
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Defining function contexts and tasks

Your plug-in can use a function context to create and manage a task, which is a kind of lightweight process
that runs cooperatively on Lightroom's main (user interface) thread. If your service defines a lengthy
export operation that would block the main Lightroom process, you should run it as a background task,
using functions such as
as those in the
The
LrFunctionContext
can register any number of cleanup handlers to respond to the success or failure of a function. You must
create property tables within a function context, so that Lightroom can remove notifications when the
table is no longer needed.
You do not create instances of
exist only for the lifetime of the function call or task. Access the calling functions, such as
LrFunctionContext.postAsyncTaskWithContext()
functionContext
provide. Use the passed object to provide the cleanup handlers for the called function execution.
In general, you are responsible for creating tasks when needed. There are some exceptions, however. Many
of the plug-in callback functions in the export and publish APIs are called from within tasks that Lightroom
starts. These are marked as such in the API reference.
For details of the

Including scripts with require()

Lightroom defines a
the version that exists in Lua. The
another Lua file in the same plug-in. On the first call, this file is loaded and executed in the context of its
plug-in; the return value is saved. If the
value is used (unless the entire plug-in has been garbage collected, in which case the required file is
loaded and executed again).
A script to be executed this way typically has the effect of defining a table containing a suite of functions.
For example:
SomeFile.lua
SomeFile = {}
-- Typically a file that is required will define a global table whose name
-- matches the file name.
-- Note that this global is defined in a special function environment for your
-- plug-in and does not affect Lightroom as a whole.
-- You can give this table any name that does not conflict with built-in names
-- and keywords from Lua and Lightroom. In general, avoid names that start with
-- Lr to avoid conflicts with future versions of Lightroom.
function SomeFile.doSomething( arg )
return tostring( arg )
end
Usage of require()
require 'SomeFile.lua'
-- Causes SomeFile.lua to be executed and the value of SomeFile defined above
-- becomes available in the scope of this file.
LrFunctionContext.postAsyncTaskWithContext()
namespace, are only available when called from within a background task.
LrHttp
object helps you clean up resources following the execution of a function. You
LrFunctionContext
object is passed as the first parameter of the call, followed by any other parameters you
LrFunctionContext
function that works in a similar, but more narrowly-defined, fashion from
require()
require()
directly. They are created by the calling functions, and
, directly from the imported namespace. A
and functions, see the Lightroom SDK API Reference.
LrTasks
function takes a single parameter, which is the name of
function is called again in the same plug-in, its saved
require()
The Lightroom SDK scripting environment 20
. Some API functions, such