fix(pointcloud_preprocessor): fix launch error

sensing/pointcloud_preprocessor/launch/preprocessor.launch.py

@@ -15,41 +15,25 @@
 import launch
 from launch.actions import DeclareLaunchArgument
 from launch.actions import LogInfo
+from launch.actions import OpaqueFunction
 from launch.substitutions import LaunchConfiguration
 from launch.substitutions import PythonExpression
 from launch_ros.actions import ComposableNodeContainer
 from launch_ros.descriptions import ComposableNode
 
 
-def generate_launch_description():
+def launch_setup(context, *args, **kwargs):
     ns = "pointcloud_preprocessor"
     pkg = "pointcloud_preprocessor"
 
-    # declare launch arguments
-    input_points_raw_list_param = DeclareLaunchArgument(
-        "input_points_raw_list",
-        default_value="['/points_raw']",
-        description="Input pointcloud topic_name list as a string_array. "
-        "To subscribe multiple topics, write as: \"['/points_raw0', '/points_raw1', ...]\"",
-    )
-
-    output_points_raw_param = DeclareLaunchArgument(
-        "output_points_raw", default_value="/points_raw/cropbox/filtered"
-    )
-
-    tf_output_frame_param = DeclareLaunchArgument("tf_output_frame", default_value="base_link")
-
-    # set concat filter as a component
-    separate_concatenate_node_and_timesync_node_str = DeclareLaunchArgument(
-        "separate_concatenate_node_and_timesync_node",
-        default_value="false",
-        description="Set True to separate concatenate node and timesync node. which will cause to larger memory usage.",
-    )
-    separate_concatenate_node_and_timesync_node = (
-        separate_concatenate_node_and_timesync_node_str.lower() == "true"
+    separate_concatenate_node_and_timesync_node = LaunchConfiguration(
+        "separate_concatenate_node_and_timesync_node"
+    ).perform(context)
+    is_separate_concatenate_node_and_timesync_node = (
+        separate_concatenate_node_and_timesync_node.lower() == "true"
     )
 
-    if not separate_concatenate_node_and_timesync_node:
+    if not is_separate_concatenate_node_and_timesync_node:
         sync_and_concat_component = ComposableNode(
             package=pkg,
             plugin="pointcloud_preprocessor::PointCloudConcatenateDataSynchronizerComponent",
@@ -150,13 +134,30 @@ def generate_launch_description():
             ]
         )
     )
+    return [container, log_info]
 
-    return launch.LaunchDescription(
-        [
-            input_points_raw_list_param,
-            output_points_raw_param,
-            tf_output_frame_param,
-            container,
-            log_info,
-        ]
+
+def generate_launch_description():
+    launch_arguments = []
+
+    def add_launch_arg(name: str, default_value=None, description=None):
+        # a default_value of None is equivalent to not passing that kwarg at all
+        launch_arguments.append(
+            DeclareLaunchArgument(name, default_value=default_value, description=description)
+        )
+
+    add_launch_arg(
+        "input_points_raw_list",
+        ["/points_raw"],
+        "Input pointcloud topic_name list as a string_array. "
+        "To subscribe multiple topics, write as: \"['/points_raw0', '/points_raw1', ...]\"",
     )
+    add_launch_arg("output_points_raw", "/points_raw/cropbox/filtered")
+    add_launch_arg("tf_output_frame", "base_link")
+    add_launch_arg(
+        "separate_concatenate_node_and_timesync_node",
+        "true",
+        "Set True to separate concatenate node and timesync node. which will cause to larger memory usage.",
+    )
+
+    return launch.LaunchDescription(launch_arguments + [OpaqueFunction(function=launch_setup)])