my_custom_message publish error

[lin123-stack]

Issue template

• Hardware description: stm32-e407
• RTOS: freertos
• Installation type: micro_ros_setup ubuntu20.04
• Version or commit hash: foxy

Steps to reproduce the issue

first step : Custom message type here is my msg: float32 linear_x float32 linear_y float32 angular_z

second step: here is my app.c:

#include <stdio.h>
#include <unistd.h>

#include <rcl/rcl.h>
#include <rcl/error_handling.h>
//#include <std_msgs/msg/int32.h>
#include <my_custom_message/msg/velocities.h> 

#include <rclc/rclc.h>
#include <rclc/executor.h>

#ifdef ESP_PLATFORM
#include "freertos/FreeRTOS.h"
#include "freertos/task.h"
#endif

#define RCCHECK(fn) { rcl_ret_t temp_rc = fn; if((temp_rc != RCL_RET_OK)){printf("Failed status on line %d: %d. Aborting.\n",__LINE__,(int)temp_rc);vTaskDelete(NULL);}}
#define RCSOFTCHECK(fn) { rcl_ret_t temp_rc = fn; if((temp_rc != RCL_RET_OK)){printf("Failed status on line %d: %d. Continuing.\n",__LINE__,(int)temp_rc);}}

rcl_publisher_t publisher;
//std_msgs__msg__Int32 msg;
my_custom_message__msg__Velocities msg;

void timer_callback(rcl_timer_t * timer, int64_t last_call_time)
{
    RCLC_UNUSED(last_call_time);
    if (timer != NULL) {
        RCSOFTCHECK(rcl_publish(&publisher, &msg, NULL));
        //msg.linear_x++;
        //msg.linear_y++;
        //msg.angular_z++;
    }
}

void appMain(void * arg)
{
    rcl_allocator_t allocator = rcl_get_default_allocator();
    rclc_support_t support;

    // create init_options
    RCCHECK(rclc_support_init(&support, 0, NULL, &allocator));

    // create node
    rcl_node_t node;
    RCCHECK(rclc_node_init_default(&node, "freertos_velocities_publisher", "", &support));

    // create publisher
    RCCHECK(rclc_publisher_init_default(
        &publisher,
        &node,
        ROSIDL_GET_MSG_TYPE_SUPPORT(my_custom_message, msg, Velocities),
        "freertos_Velocities_publisher"));

    // create timer,
    rcl_timer_t timer;
    const unsigned int timer_timeout = 1000;
    RCCHECK(rclc_timer_init_default(
        &timer,
        &support,
        RCL_MS_TO_NS(timer_timeout),
        timer_callback));

    // create executor
    rclc_executor_t executor;
    RCCHECK(rclc_executor_init(&executor, &support.context, 1, &allocator));
    RCCHECK(rclc_executor_add_timer(&executor, &timer));

    msg.linear_x = 1.0;
    msg.linear_y =1.0 ;
    msg.angular_z = 1.0;
    while(1){
        rclc_executor_spin_some(&executor, RCL_MS_TO_NS(100));
        usleep(100000);
    }

    // free resources
    RCCHECK(rcl_publisher_fini(&publisher, &node))
    RCCHECK(rcl_node_fini(&node))

    vTaskDelete(NULL);
}

step 3：

ros2 topic echo /freertos_Velocities_publisher 
Traceback (most recent call last):
  File "/opt/ros/foxy/bin/ros2", line 11, in <module>
    load_entry_point('ros2cli==0.9.9', 'console_scripts', 'ros2')()
  File "/opt/ros/foxy/lib/python3.8/site-packages/ros2cli/cli.py", line 67, in main
    rc = extension.main(parser=parser, args=args)
  File "/opt/ros/foxy/lib/python3.8/site-packages/ros2topic/command/topic.py", line 41, in main
    return extension.main(args=args)
  File "/opt/ros/foxy/lib/python3.8/site-packages/ros2topic/verb/echo.py", line 81, in main
    return main(args)
  File "/opt/ros/foxy/lib/python3.8/site-packages/ros2topic/verb/echo.py", line 95, in main
    message_type = get_msg_class(node, args.topic_name, include_hidden_topics=True)
  File "/opt/ros/foxy/lib/python3.8/site-packages/ros2topic/api/__init__.py", line 88, in get_msg_class
    msg_class = _get_msg_class(node, topic, include_hidden_topics)
  File "/opt/ros/foxy/lib/python3.8/site-packages/ros2topic/api/__init__.py", line 133, in _get_msg_class
    return get_message(message_type)
  File "/opt/ros/foxy/lib/python3.8/site-packages/rosidl_runtime_py/utilities.py", line 28, in get_message
    interface = import_message_from_namespaced_type(get_message_namespaced_type(identifier))
  File "/opt/ros/foxy/lib/python3.8/site-packages/rosidl_runtime_py/import_message.py", line 30, in import_message_from_namespaced_type
    module = importlib.import_module(
  File "/usr/lib/python3.8/importlib/__init__.py", line 127, in import_module
    return _bootstrap._gcd_import(name[level:], package, level)
  File "<frozen importlib._bootstrap>", line 1014, in _gcd_import
  File "<frozen importlib._bootstrap>", line 991, in _find_and_load
  File "<frozen importlib._bootstrap>", line 961, in _find_and_load_unlocked
  File "<frozen importlib._bootstrap>", line 219, in _call_with_frames_removed
  File "<frozen importlib._bootstrap>", line 1014, in _gcd_import
  File "<frozen importlib._bootstrap>", line 991, in _find_and_load
  File "<frozen importlib._bootstrap>", line 973, in _find_and_load_unlocked
ModuleNotFoundError: No module named 'my_custom_message'

I don't know what the problem is？

[lin123-stack]

I solved it.