MDL-71344 questions: Improve event handler for Drag n Drop family

question/type/ddimageortext/amd/src/question.js

@@ -947,6 +947,12 @@ define(['jquery', 'core/dragdrop', 'core/key_codes'], function($, dragDrop, keys
          */
         eventHandlersInitialised: false,
 
+        /**
+         * {Object} ensures that the drag event handlers are only initialised once per question,
+         * indexed by containerId (id on the .que div).
+         */
+        dragEventHandlersInitialised: {},
+
         /**
          * {boolean} is printing or not.
          */
@@ -977,14 +983,22 @@ define(['jquery', 'core/dragdrop', 'core/key_codes'], function($, dragDrop, keys
                 questionManager.setupEventHandlers();
                 questionManager.eventHandlersInitialised = true;
             }
+            if (!questionManager.dragEventHandlersInitialised.hasOwnProperty(containerId)) {
+                questionManager.dragEventHandlersInitialised[containerId] = true;
+                // We do not use the body event here to prevent the other event on Mobile device, such as scroll event.
+                var questionContainer = document.getElementById(containerId);
+                if (questionContainer.classList.contains('ddimageortext') &&
+                    !questionContainer.classList.contains('qtype_ddimageortext-readonly')) {
+                    // TODO: Convert all the jQuery selectors and events to native Javascript.
+                    questionManager.addEventHandlersToDrag($(questionContainer).find('.draghome'));
+                }
+            }
         },
 
         /**
          * Set up the event handlers that make this question type work. (Done once per page.)
          */
         setupEventHandlers: function() {
-            // We do not use the body event here to prevent the other event on Mobile device, such as scroll event.
-            questionManager.addEventHandlersToDrag($('.que.ddimageortext:not(.qtype_ddimageortext-readonly) .draghome'));
             $('body')
                 .on('keydown',
                     '.que.ddimageortext:not(.qtype_ddimageortext-readonly) .dropzones .dropzone',

question/type/ddmarker/amd/src/question.js

@@ -682,6 +682,12 @@ define(['jquery', 'core/dragdrop', 'qtype_ddmarker/shapes', 'core/key_codes'], f
          */
         eventHandlersInitialised: false,
 
+        /**
+         * {Object} ensures that the marker event handlers are only initialised once per question,
+         * indexed by containerId (id on the .que div).
+         */
+        markerEventHandlersInitialised: {},
+
         /**
          * {boolean} is printing or not.
          */
@@ -711,15 +717,23 @@ define(['jquery', 'core/dragdrop', 'qtype_ddmarker/shapes', 'core/key_codes'], f
                 questionManager.setupEventHandlers();
                 questionManager.eventHandlersInitialised = true;
             }
+            if (!questionManager.markerEventHandlersInitialised.hasOwnProperty(containerId)) {
+                questionManager.markerEventHandlersInitialised[containerId] = true;
+                // We do not use the body event here to prevent the other event on Mobile device, such as scroll event.
+                var questionContainer = document.getElementById(containerId);
+                if (questionContainer.classList.contains('ddmarker') &&
+                    !questionContainer.classList.contains('qtype_ddmarker-readonly')) {
+                    // TODO: Convert all the jQuery selectors and events to native Javascript.
+                    questionManager.addEventHandlersToMarker($(questionContainer).find('div.draghomes .marker'));
+                    questionManager.addEventHandlersToMarker($(questionContainer).find('div.droparea .marker'));
+                }
+            }
         },
 
         /**
          * Set up the event handlers that make this question type work. (Done once per page.)
          */
         setupEventHandlers: function() {
-            // We do not use the body event here to prevent the other event on Mobile device, such as scroll event.
-            questionManager.addEventHandlersToMarker($('.que.ddmarker:not(.qtype_ddmarker-readonly) div.draghomes .marker'));
-            questionManager.addEventHandlersToMarker($('.que.ddmarker:not(.qtype_ddmarker-readonly) div.droparea .marker'));
             $(window).on('resize', function() {
                 questionManager.handleWindowResize(false);
             });

question/type/ddwtos/amd/src/ddwtos.js

@@ -734,6 +734,12 @@ define(['jquery', 'core/dragdrop', 'core/key_codes'], function($, dragDrop, keys
          */
         eventHandlersInitialised: false,
 
+        /**
+         * {Object} ensures that the drag event handlers are only initialised once per question,
+         * indexed by containerId (id on the .que div).
+         */
+        dragEventHandlersInitialised: {},
+
         /**
          * {boolean} is keyboard navigation or not.
          */
@@ -756,14 +762,22 @@ define(['jquery', 'core/dragdrop', 'core/key_codes'], function($, dragDrop, keys
                 questionManager.setupEventHandlers();
                 questionManager.eventHandlersInitialised = true;
             }
+            if (!questionManager.dragEventHandlersInitialised.hasOwnProperty(containerId)) {
+                questionManager.dragEventHandlersInitialised[containerId] = true;
+                // We do not use the body event here to prevent the other event on Mobile device, such as scroll event.
+                var questionContainer = document.getElementById(containerId);
+                if (questionContainer.classList.contains('ddwtos') &&
+                    !questionContainer.classList.contains('qtype_ddwtos-readonly')) {
+                    // TODO: Convert all the jQuery selectors and events to native Javascript.
+                    questionManager.addEventHandlersToDrag($(questionContainer).find('span.draghome'));
+                }
+            }
         },
 
         /**
          * Set up the event handlers that make this question type work. (Done once per page.)
          */
         setupEventHandlers: function() {
-            // We do not use the body event here to prevent the other event on Mobile device, such as scroll event.
-            questionManager.addEventHandlersToDrag($('.que.ddwtos:not(.qtype_ddwtos-readonly) span.draghome'));
             $('body')
                 .on('keydown',
                     '.que.ddwtos:not(.qtype_ddwtos-readonly) span.drop',