!1 add chapt4/chapt4_ws/src/demo_cpp_service/launch/actions.launch.py.

Merge pull request !1 from 梁琛/N/A

chapt4/chapt4_ws/src/demo_cpp_service/launch/actions.launch.py

@@ -0,0 +1,39 @@
+import launch
+import launch_ros
+from ament_index_python.packages import get_package_share_directory
+
+def generate_launch_description():
+    action_declare_startup_rqt = launch.actions.DeclareLaunchArgument('startup_rqt', default_value='False')
+    startup_rqt = launch.substitutions.LaunchConfiguration('startup_rqt')
+
+    #动作1-启动其他launch
+    multisim_launch_path = [get_package_share_directory('turtlesim'), '/launch/','multisim.launch.py']
+    action_include_launch = launch.actions.IncludeLaunchDescription(
+        launch.launch_description_sources.PythonLaunchDescriptionSource(
+            multisim_launch_path
+        )
+    )
+
+    #动作2-打印数据
+    action_log_info = launch.actions.LogInfo(msg=str(multisim_launch_path))
+
+    #动作3-执行进程，其实就是执行一个命令行 ros2 topic list
+    action_topic_list = launch.actions.ExecuteProcess(
+        condition=launch.conditions.IfCondition(startup_rqt),
+        cmd=['rqt'],
+    )
+
+    #动作4-组织动作成组，把多个动作放到一组
+    action_group = launch.actions.GroupAction([
+        #动作5-定时器
+        launch.actions.TimerAction(period=2.0, actions=[action_include_launch]),
+        launch.actions.TimerAction(period=2.0, actions=[action_topic_list]),      
+    ])
+
+
+    return launch.LaunchDescription([
+        #actions动作
+        action_declare_startup_rqt,
+        action_log_info,
+        action_group
+    ])