BTComObj for Lazarus

BTComObj is a specialized Free Pascal utility unit designed to facilitate the creation and implementation of Microsoft COM (Component Object Model) servers within the Windows ecosystem. Core Purpose & Functionality

While standard Lazarus code uses the default ComObj unit for basic COM automation, BTComObj provides a foundational base class (TBTComObject) that streamlines writing lightweight Windows COM objects. It wraps standard Windows COM interfaces, handling lifetime management and class factory registration so you can expose custom Free Pascal functions to external Windows applications (like Excel, Word, or custom C++/.NET software). Key Technical Characteristics

Windows Specific: Because COM is a proprietary Microsoft architecture, BTComObj is strictly designed for Windows-family operating systems. It will not compile or run on cross-platform targets like Linux or macOS.

Lightweight Implementation: It is often utilized in direct, low-overhead library environments (such as custom player libraries or plugin systems) where developers want to spin up a COM server without heavy framework baggage.

Interface-Driven: Developers inherit from TBTComObject and implement standard or custom type-safe IUnknown or IDispatch interfaces using the stdcall calling convention. Code Example: Implementing a COM Server

Implementing a quick COM object using BTComObj inside Lazarus looks like this:

unit MyCustomComServer; {\(mode objfpc}{\)H+} interface uses SysUtils, Windows, BTComObj, MyTestInterfaceUnit; type // Inherit from TBTComObject and implement your custom COM interface TMyComObject = class(TBTComObject, IMyCustomInterface) public // Methods must use standard Windows call convention function DisplayAlert(Title: PWideChar; MessageText: PWideChar): HResult; stdcall; end; implementation function TMyComObject.DisplayAlert(Title: PWideChar; MessageText: PWideChar): HResult; stdcall; begin MessageBoxW(0, MessageText, Title, MB_OK or MB_TOPMOST); Result := S_OK; end; initialization // Class factories and initialization rules follow here… end. Use code with caution. Clarification on a Common Confusion

Because of its name, developers looking to integrate Bluetooth into Lazarus often mistake BTComObj for a wireless communications library.

BTComObj has nothing to do with Bluetooth. The “BT” in this context refers to the specific third-party library ecosystem or internal project prefix it was bundled with (such as early media player/dsplayer libraries).

For actual Bluetooth support, you should use the official bluetoothlaz package (which binds to Linux BlueZ), the third-party Pascal-Bindings-For-SimpleBLE, or the commercial wcl-lazarus-demos framework.

If you are trying to use this component for a project, tell me:

Are you building a Windows-only COM server, or looking to automate an external app?

Did you arrive at this unit while looking for Bluetooth communication capabilities?

Do you have an existing Delphi project you are trying to port into Lazarus? COM Server implementation (windows) – Lazarus Forum