added ability to unsubscribe from a topic

Author: amalnanavati

feeding_web_app_ros2_test/feeding_web_app_ros2_test/FaceDetection.py

@@ -79,6 +79,9 @@ def toggle_face_detection_callback(self, request, response):
         Callback function for the ToggleFaceDetection service. Safely toggles
         the face detection on or off depending on the request.
         """
+        self.get_logger().info(
+            "Incoming service request. turn_on: %s" % (request.turn_on)
+        )
         if request.turn_on:
             # Reset counters
             self.num_consecutive_images_without_face = 0

feedingwebapp/src/Pages/Home/MealStates/BiteInitiation.jsx

@@ -8,7 +8,13 @@ import Row from 'react-bootstrap/Row'
 
 // Local Imports
 import '../Home.css'
-import { connectToROS, createROSService, createROSServiceRequest, subscribeToROSTopic } from '../../../ros/ros_helpers'
+import {
+  connectToROS,
+  createROSService,
+  createROSServiceRequest,
+  subscribeToROSTopic,
+  unsubscribeFromROSTopic
+} from '../../../ros/ros_helpers'
 import { convertRemToPixels, scaleWidthHeightToWindow } from '../../../helpers'
 import {
   FACE_DETECTION_IMG_TOPIC,
@@ -63,7 +69,13 @@ const BiteInitiation = (props) => {
     [setDetectedMouthCenter, setMouthDetected, readyForBite]
   )
   useEffect(() => {
-    subscribeToROSTopic(ros.current, FACE_DETECTION_TOPIC, FACE_DETECTION_TOPIC_MSG, faceDetectionCallback)
+    let topic = subscribeToROSTopic(ros.current, FACE_DETECTION_TOPIC, FACE_DETECTION_TOPIC_MSG, faceDetectionCallback)
+    // In practice, because the values passed in in the second argument of
+    // useEffect will not change on re-renders, this return statement will
+    // only be called when the component unmounts.
+    return () => {
+      unsubscribeFromROSTopic(topic, faceDetectionCallback)
+    }
   }, [faceDetectionCallback])
 
   // Create the ROS Service. This is created in local state to avoid

feedingwebapp/src/ros/ros_helpers.js

@@ -75,6 +75,16 @@ export function subscribeToROSTopic(ros, topicName, topicType, callback) {
   return topic
 }
 
+/**
+ * Unsubscribe from a ROS topic.
+ *
+ * @param {object} topic The ROSLIB.Topic.
+ * @param {function} callback The callback function to unsubscribe.
+ */
+export function unsubscribeFromROSTopic(topic, callback) {
+  topic.unsubscribe(callback)
+}
+
 /**
  * Create a ROS Service.
  *