3.3.1 Implementing dispinterfaces in Lua

3.3.1 Implementing dispinterfaces in Lua

The Automation binding has a C++ class called tLuaDispatch that implements a generic IDispatch interface. The implementation of this class translates the method calls and property accesses done on the objects of this class to Lua calls and table accesses. So, one may implement a dispinterface entirely in Lua, provided it has a type library describing it. This type library may be a stand-alone one (referenced by its location on the file system) or may be associated with some registered component. In this case, it may be referenced by the ProgID of the component.

The C++ objects of this class can be used in any place where an IDispatch or IUnknown interface is expected. LuaCOM takes care of these conversion. Follows a sample implementation of a dispinterface in Lua.

-- Creates and fills the Lua table that will implement the
-- COM interface
events_table = {}
function events_table:AfterUpdate()
  print("AfterUpdate called!")
end
-- Here we implement the interface DCalendarEvents, which is part
-- of the Microsoft(R) Calendar object, whose ProgID is MSCAL.Calendar
events_obj = luacom.ImplInterface(
  events_table, 
  "MSCAL.Calendar",
  "DCalendarEvents")
-- Checks for errors
--
if events_obj == nil then
  print("Implementation failed")
  exit(1)
end
-- Tests the interface: this must generate a call to the events:AfterUpdate
-- defined above
--
events_obj:AfterUpdate()

If the interface to be implemented is described in a stand-alone type library, the method ImplInterfaceFromTypelib must be used instead:

-- Creates and fills the Lua table that will implement the
-- Automation interface
hello_table = {}
function hello:Hello()
  print("Hello World!")
end
-- Here we implement the interface IHello
--
hello_obj = luacom.ImplInterfaceFromTypelib("hello.tlb","IHello")
-- Checks for errors
--
if hello_obj == nil then
  print("Implementation failed")
  os.exit(1)
end
-- Tests the interface
--
hello_obj:Hello()

Both methods return a LuaCOM object, whose corresponding IDispatch interface is implemented by the supplied table. This LuaCOM object can be passed as an argument to COM methods who expect a dispinterface or to LuaCOM API methods (like addConnection).

One can also use the NewObject method, which is best suited to the situation where one needs to create a complete component in Lua and wants to export it, so that it can be accessed through COM by any running application.