add example of registering custom parameter validation callbacks (#273)

* add example of registering custom parameter validation callbacks

* add ':' before parameter value

demo_nodes_cpp/CMakeLists.txt

@@ -48,6 +48,7 @@ custom_executable(parameters list_parameters_async)
 custom_executable(parameters parameter_events)
 custom_executable(parameters parameter_events_async)
 custom_executable(parameters parameter_node)
+custom_executable(parameters even_parameters_node)
 custom_executable(parameters set_and_get_parameters)
 custom_executable(parameters set_and_get_parameters_async)
 

demo_nodes_cpp/src/parameters/even_parameters_node.cpp

@@ -0,0 +1,86 @@
+// Copyright 2018 Open Source Robotics Foundation, Inc.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#include <memory>
+#include <vector>
+
+#include "rclcpp/rclcpp.hpp"
+
+class EvenParameterNode : public rclcpp::Node
+{
+public:
+  EvenParameterNode()
+  : Node("even_parameters_node")
+  {
+    // Declare a parameter change request callback
+    // This function will enforce that only setting even integer parameters is allowed
+    // any other change will be discarded
+    auto param_change_callback =
+      [this](std::vector<rclcpp::Parameter> parameters) -> rcl_interfaces::msg::SetParametersResult
+      {
+        auto result = rcl_interfaces::msg::SetParametersResult();
+        result.successful = true;
+        for (auto parameter : parameters) {
+          rclcpp::ParameterType parameter_type = parameter.get_type();
+          if (rclcpp::ParameterType::PARAMETER_NOT_SET == parameter_type) {
+            RCLCPP_INFO(this->get_logger(),
+              "parameter '%s' deleted successfully",
+              parameter.get_name().c_str()
+            );
+            result.successful &= true;
+          } else if (rclcpp::ParameterType::PARAMETER_INTEGER == parameter_type) {
+            if (parameter.as_int() % 2 != 0) {
+              RCLCPP_INFO(this->get_logger(),
+                "Requested value '%d' for parameter '%s' is not an even number:"
+                " rejecting change...",
+                parameter.as_int(),
+                parameter.get_name().c_str()
+              );
+              result.successful = false;
+            } else {
+              RCLCPP_INFO(this->get_logger(),
+                "parameter '%s' has changed and is now: %s",
+                parameter.get_name().c_str(),
+                parameter.value_to_string().c_str()
+              );
+              result.successful &= true;
+            }
+          } else {
+            RCLCPP_INFO(this->get_logger(),
+              "only integer parameters can be set\n"
+              "requested value for parameter '%s' is not an even number, rejecting change...",
+              parameter.get_name().c_str()
+            );
+            result.successful = false;
+          }
+        }
+        return result;
+      };
+    this->register_param_change_callback(param_change_callback);
+  }
+};
+
+int main(int argc, char ** argv)
+{
+  // Force flush of the stdout buffer.
+  setvbuf(stdout, NULL, _IONBF, BUFSIZ);
+
+  rclcpp::init(argc, argv);
+
+  auto node = std::make_shared<EvenParameterNode>();
+
+  rclcpp::spin(node);
+  rclcpp::shutdown();
+  return 0;
+}