[Documentation] - Create and build messages

[xas]

Hi,

I am a dotnet dev, but totally new with ROS2.

I did ok with some python tutorials, but now trying to migrate the code to ROS2.NET

I am trying to understand how to build any message (currently action msg) but I am failing miserably.

I am not sure how correctly fill the CMakeLists.txt (currently it is just by guessing 😞). My questions are:

• Can I create a new workspace with a new package only with action messages ? Or should I keep it into the dotnet ws ?
• I have some errors when trying to colcon build (see below), but I am not an expert of cmake, so I must be missing some packages/linker/...?

Can someone guide me ?

PS: The building errors:

CMake Error: Cannot determine link language for target "cloudnet__rosidl_typesupport_fastrtps_c".
CMake Error: CMake can not determine linker language for target: cloudnet__rosidl_typesupport_fastrtps_c
CMake Error: Cannot determine link language for target "cloudnet__rosidl_typesupport_fastrtps_cpp".
CMake Error: CMake can not determine linker language for target: cloudnet__rosidl_typesupport_fastrtps_cpp
CMake Error: Cannot determine link language for target "cloudnet__rosidl_typesupport_c".
CMake Error: CMake can not determine linker language for target: cloudnet__rosidl_typesupport_c
CMake Error: Cannot determine link language for target "cloudnet__rosidl_typesupport_introspection_cpp".
CMake Error: CMake can not determine linker language for target: cloudnet__rosidl_typesupport_introspection_cpp
CMake Error: Cannot determine link language for target "cloudnet__rosidl_typesupport_cpp".
CMake Error: CMake can not determine linker language for target: cloudnet__rosidl_typesupport_cpp

The CMakeLists.txt

cmake_minimum_required(VERSION 3.5)
project(cloudnet C)

find_package(ament_cmake REQUIRED)
find_package(builtin_interfaces REQUIRED)
find_package(rosidl_default_generators REQUIRED)
find_package(unique_identifier_msgs REQUIRED)
find_package(rosidl_default_generators REQUIRED)

rosidl_generate_interfaces(${PROJECT_NAME}
  "action/OneAction.action"
  DEPENDENCIES builtin_interfaces action_msgs unique_identifier_msgs
  ADD_LINTER_TESTS
)

ament_export_dependencies(rosidl_default_runtime)
ament_package()

[hoffmann-stefan]

Hi @xas,

sorry for the late reply.

• Can I create a new workspace with a new package only with action messages ? Or should I keep it into the dotnet ws ?

You can add your message package to the ros2 dotnet workspace or any other workspace that overlays your ros2 dotnet workspace, see the official overriding workspace documentation. Be sure to source the correct workspaces at any step. But this is nothing specific to ros2 dotnet.

I have some errors when trying to colcon build (see below), but I am not an expert of cmake, so I must be missing some packages/linker/...?

There should be no difference for defining the messages compared to standard ros c++ and python.
Does your message package compile if you build it in a non dotnet workspace for use with c++ or python?