Minimal Example Launch File

Oct 13, 2025 by magicalceylontours.com 102 views

[bug] Ignored lifecycle state Event/EventHandler in launch file

When debugging a ROS Lifecycle node using the launch file, the launch.actions.EmitEvent and launch_ros.events.lifecycle.ChangeState actions seem to be ignored. Even if the state is changed manually via ros2 lifecycle <node_name> <state>, the EventHandler of the launch file does not work as expected.

What is the Bug?

The bug occurs when trying to activate a ROS Lifecycle node from a launch file using launch.actions.EmitEvent and launch_ros.events.lifecycle.ChangeState. The EmitEvent action does not seem to be executed, and even if the state is changed manually, the EventHandler of the launch file does not work.

Minimal Example Launch File

The following is a minimal example launch file that demonstrates the bug:

from launch.actions import Shutdown
from launch_ros.actions import LifecycleNode
from launch_ros.actions import Node
from launch.actions import DeclareLaunchArgument, EmitEvent, RegisterEventHandler, LogInfo
from launch_ros.event_handlers import OnStateTransition
from launch_ros.events.lifecycle import ChangeState
import launch
from lifecycle_msgs.msg import Transition


def generate_launch_description():
    node = LifecycleNode(package='lifecycle', executable='lifecycle_talker',
                         name='lc_talker', namespace='', output='screen')
    # THIS DOES NOT WORK in Launch Debugging
    configure_event = EmitEvent(
        event=ChangeState(
            lifecycle_node_matcher=launch.events.matches_action(
                node),
            transition_id=Transition.TRANSITION_CONFIGURE,
        ))
    # THIS DOES NOT WORK in Launch Debugging
    state_handler = RegisterEventHandler(
        OnStateTransition(
            target_lifecycle_node=node,
            goal_state='inactive',
            entities=[
                # Log
                LogInfo(
                    msg="RegisterEventHandler worked")]))
    return LaunchDescription([
        configure_event, node, state_handler
        # Node(package='lifecycle', executable='lifecycle_listener', output='screen'),
        # Node(package='lifecycle', executable='lifecycle_service_client', output='screen',
        #      on_exit=Shutdown()),

Repro Steps

To reproduce the bug, follow these steps:

Clone the ROS Lifecycle demo code repository.
Compile the lifecycle package.
Launch debugging on the launch package.

Expected Behavior

The expected behavior is that the launch file should work as expected when run without the debugger:

Signals are emitted.
Handlers are called.
In the provided example, we should have the LogInfo message.

Additional Context

Any additional information that would be helpful for a better understanding of the bug:

The bug occurs on Linux (Ubuntu 20.04) with ROS 2 Foxy.
The bug is not specific to a particular ROS 2 distribution.
The bug is not specific to a particular version of the vscode-ros extension.

Version Information

Version of the plugin: v0.9.2
Version: 1.95.3
Commit: f1a4fb101478ce6ec82fe9627c43efbf9e98c813
Date: 2024-11-13T14:50:04.152Z
Electron: 32.2.1
ElectronBuildId: 10427718
Chromium: 128.0.6613.186
Node.js: 20.18.0
V8: 12.8.374.38-electron.0
OS: Linux x64 6.8.0-48-generic snap
Q&A: Ignored lifecycle state Event/EventHandler in launch file

Q: What is the bug?

A: The bug occurs when trying to activate a ROS Lifecycle node from a launch file using launch.actions.EmitEvent and launch_ros.events.lifecycle.ChangeState. The EmitEvent action does not seem to be executed, and even if the state is changed manually, the EventHandler of the launch file does not work.

Q: What is the expected behavior?

A: The expected behavior is that the launch file should work as expected when run without the debugger:

Signals are emitted.
Handlers are called.
In the provided example, we should have the LogInfo message.

Q: What are the repro steps?

A: To reproduce the bug, follow these steps:

Clone the ROS Lifecycle demo code repository.
Compile the lifecycle package.
Launch debugging on the launch package.

Q: What are the system requirements?

A: The bug occurs on Linux (Ubuntu 20.04) with ROS 2 Foxy.

Q: Is the bug specific to a particular ROS 2 distribution?

A: No, the bug is not specific to a particular ROS 2 distribution.

Q: Is the bug specific to a particular version of the `vscode-ros` extension?

A: No, the bug is not specific to a particular version of the vscode-ros extension.

Q: What are the version information details?

A: The version information details are as follows:

Version of the plugin: v0.9.2
Version: 1.95.3
Commit: f1a4fb101478ce6ec82fe9627c43efbf9e98c813
Date: 2024-11-13T14:50:04.152Z
Electron: 32.2.1
ElectronBuildId: 10427718
Chromium: 128.0.6613.186
Node.js: 20.18.0
V8: 12.8.374.38-electron.0
OS: Linux x64 6.8.0-48-generic snap

Q: What is the minimal example launch file?

A: The minimal example launch file is as follows:

from launch.actions import Shutdown
from launch_ros.actions import LifecycleNode
from launch_ros.actions import Node
from launch.actions import DeclareLaunchArgument, EmitEvent, RegisterEventHandler, LogInfo
from launch_ros.event_handlers import OnStateTransition
from launch_ros.events.lifecycle import ChangeState
import launch
from lifecycle_msgs.msg import Transition


def generate_launch_description():
    node = LifecycleNode(package='lifecycle', executable='lifecycle_talker',
                         name='lc_talker', namespace='', output='screen')
    # THIS DOES NOT WORK in Launch Debugging
    configure_event = EmitEvent(
        event=ChangeState(
            lifecycle_node_matcher=launch.events.matches_action(
                node),
            transition_id=Transition.TRANSITION_CONFIGURE,
        ))
    # THIS DOES NOT WORK in Launch Debugging
    state_handler = RegisterEventHandler(
        OnStateTransition(
            target_lifecycle_node=node,
            goal_state='inactive',
            entities=[
                # Log
                LogInfo(
                    msg="RegisterEventHandler worked")]))
    return LaunchDescription([
        configure_event, node, state_handler
        # Node(package='lifecycle', executable='lifecycle_listener', output='screen'),
        # Node(package='lifecycle', executable='lifecycle_service_client', output='screen',
        #      on_exit=Shutdown()),

Q: What is the final goal?

A: The final goal is to perform something similar to this example.