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一、简单实操 

1.创建/打开一个功能包 

mkdir -p my_ws/src
cd my_ws/src
ros2 pkg create my_pkg_example --build-type ament_python

2.创建Launch文件的存放目录

将所有启动文件都存储在launch包内的目录中。

目录结构如下所示：
src/my_pkg_example/launch/package.xmlpy_launch_example/resource/setup.cfgsetup.pytest/

3.修改setup.py文件

为了让 colcon 找到启动文件，我们需要使用 参数告知 Python 的安装工具我们的启动data_files文件setup。

import os
from glob import glob
from setuptools import setuppackage_name = 'my_pkg_example'setup(# Other parameters ...data_files=[# ... Other data files# Include all launch files.(os.path.join('share', package_name, 'launch'), glob(os.path.join('launch', '*launch.[pxy][yma]*')))]
)

4.编写Launch文件

在launch目录中，创建一个名为my_test.launch.py文件

import launch
import launch_ros.actionsdef generate_launch_description():return launch.LaunchDescription([launch_ros.actions.Node(package='demo_nodes_cpp',executable='talker',name='talker'),])

5.最后就可以构建并运行啦！

colcon build

ros2 launch my_pkg_example my_test.launch.py

二、大型项目中的使用技巧

1.完整代码示例

在/launch文件夹中创建一个文件launch_turtlesim.launch.py 内容如下：

import os
from ament_index_python.packages import get_package_share_directory
from launch import LaunchDescription
from launch.actions import IncludeLaunchDescription
from launch.launch_description_sources import PythonLaunchDescriptionSourcedef generate_launch_description():turtlesim_world_1 = IncludeLaunchDescription(PythonLaunchDescriptionSource([os.path.join(get_package_share_directory('launch_tutorial'), 'launch'),'/turtlesim_world_1.launch.py']))broadcaster_listener_nodes = IncludeLaunchDescription(PythonLaunchDescriptionSource([os.path.join(get_package_share_directory('launch_tutorial'), 'launch'),'/broadcaster_listener.launch.py']),launch_arguments={'target_frame': 'carrot1'}.items(),)mimic_node = IncludeLaunchDescription(PythonLaunchDescriptionSource([os.path.join(get_package_share_directory('launch_tutorial'), 'launch'),'/mimic.launch.py']))fixed_frame_node = IncludeLaunchDescription(PythonLaunchDescriptionSource([os.path.join(get_package_share_directory('launch_tutorial'), 'launch'),'/fixed_broadcaster.launch.py']))rviz_node = IncludeLaunchDescription(PythonLaunchDescriptionSource([os.path.join(get_package_share_directory('launch_tutorial'), 'launch'),'/turtlesim_rviz.launch.py']))return LaunchDescription([turtlesim_world_1,broadcaster_listener_nodes,mimic_node,fixed_frame_node,rviz_node])

2.内包含turtlesim_world_1.launch.py文件

import os
from ament_index_python.packages import get_package_share_directory
from launch import LaunchDescription
from launch_ros.actions import Nodedef generate_launch_description():config = os.path.join(get_package_share_directory('launch_tutorial'),'config','turtlesim.yaml')return LaunchDescription([Node(package='turtlesim',executable='turtlesim_node',namespace='turtlesim2',name='sim',parameters=[config])])

3.参数设置

import os
from ament_index_python.packages import get_package_share_directory
from launch import LaunchDescription
from launch_ros.actions import Nodedef generate_launch_description():config = os.path.join(get_package_share_directory('launch_tutorial'),'config','turtlesim.yaml')return LaunchDescription([Node(package='turtlesim',executable='turtlesim_node',namespace='turtlesim2',name='sim',parameters=[config])])

现我们在 /config 文件夹中创建一个配置文件turtlesim.yaml ，它将由我们的启动文件加载。

/turtlesim2/sim:ros__parameters:background_b: 255background_g: 86background_r: 150/turtlesim3/sim:background_bbackground_gbackground_r我们可以使用通配符语法，而不是为使用相同参数的同一节点创建新配置
/**:ros__parameters:background_b: 255background_g: 86background_r: 150

加载相同的 YAML 文件不会影响第三个turtlesim 世界的外观。原因是它的参数存储在另一个命名空间下。

4.ROS2节点复用

现在创建一个broadcaster_listener.launch.py文件

from launch import LaunchDescription
from launch.actions import DeclareLaunchArgument
from launch.substitutions import LaunchConfiguration
from launch_ros.actions import Nodedef generate_launch_description():return LaunchDescription([DeclareLaunchArgument('target_frame', default_value='turtle1',description='Target frame name.'),Node(package='turtle_tf2_py',executable='turtle_tf2_broadcaster',name='broadcaster1',parameters=[{'turtlename': 'turtle1'}]),Node(package='turtle_tf2_py',executable='turtle_tf2_broadcaster',name='broadcaster2',parameters=[{'turtlename': 'turtle2'}]),Node(package='turtle_tf2_py',executable='turtle_tf2_listener',name='listener',parameters=[{'target_frame': LaunchConfiguration('target_frame')}]),])

在此文件中，我们声明了target_frame默认值为 的启动参数turtle1。默认值意味着启动文件可以接收参数以转发到其节点，或者如果未提供参数，它将传递默认值到其节点。

之后，我们turtle_tf2_broadcaster在启动期间使用不同的名称和参数两次使用该节点。这允许我们复制相同的节点而不会发生冲突。

我们还启动一个turtle_tf2_listener节点并设置target_frame上面声明和获取的参数。

5.参数覆盖 

我们broadcaster_listener.launch.py在顶级启动文件中调用了该文件。除此之外，我们还传递了它的target_frame启动参数，如下所示：

broadcaster_listener_nodes = IncludeLaunchDescription(PythonLaunchDescriptionSource([os.path.join(get_package_share_directory('launch_tutorial'), 'launch'),'/broadcaster_listener.launch.py']),launch_arguments={'target_frame': 'carrot1'}.items(),)

此语法允许我们将默认目标目标框架更改为carrot1。如果您想turtle2跟随turtle1而不是跟随carrot1，只需删除定义的行即可launch_arguments。这将分配target_frame其默认值，即turtle1

6.重新映射 

现在创建一个mimic.launch.py文件

from launch import LaunchDescription
from launch_ros.actions import Nodedef generate_launch_description():return LaunchDescription([Node(package='turtlesim',executable='mimic',name='mimic',remappings=[('/input/pose', '/turtle2/pose'),('/output/cmd_vel', '/turtlesim2/turtle1/cmd_vel'),])])

该启动文件将启动mimic节点，该节点将向一个turtlesim发出命令以跟随另一个。
该节点旨在接收主题上的目标姿势/input/pose。
在我们的例子中，我们想要从/turtle2/pose主题重新映射目标姿势。
最后，我们将/output/cmd_vel主题重新映射到/turtlesim2/turtle1/cmd_vel。

7.千万记住更新setup.py 

import os
from glob import glob
from setuptools import setup
...data_files=[...(os.path.join('share', package_name, 'launch'),glob(os.path.join('launch', '*.launch.py'))),(os.path.join('share', package_name, 'config'),glob(os.path.join('config', '*.yaml'))),],

8.最后就可以构建并运行啦！