Fix Keyboard and DnD incompatibility (#1067) (#1445)

`dgrid/extensions/DnD` uses `dojo/dnd/Source` which registers an event handler
using `on(node, touch.press)`. `touch.press` evaluates to `'pointerdown'` in
browsers that support pointer events, and when the `'pointerdown'` listener is
registered the `'mousedown'` listener is never called. This change causes
Keyboard to use `touch.press` when DnD is being used. It also exposes a new
configuration property, `mouseDownEventType`, which enables developers to
further customize this behavior.

Keyboard.js

@@ -37,6 +37,10 @@ define([
 		//		of the instance) for key events within the grid's header row.
 		headerKeyMap: null,
 
+		// mouseDownEventType: dojo/on compatible event type
+		//		Event type to use for Keyboard's mouse down listener that sets focus.
+		mouseDownEventType: 'mousedown',
+
 		postMixInProperties: function () {
 			this.inherited(arguments);
 
@@ -141,7 +145,7 @@ define([
 					);
 				}
 
-				grid._listeners.push(on(areaNode, 'mousedown', function (event) {
+				grid._listeners.push(on(areaNode, grid.mouseDownEventType, function (event) {
 					if (!handledEvent(event)) {
 						grid._focusOnNode(event.target, isHeader, event);
 					}

doc/components/mixins/Keyboard.md

@@ -34,6 +34,7 @@ Property | Description
 `pageSkip` | Number indicating how many rows to navigate when page up or page down is pressed.  Defaults to `10`.
 `keyMap` | Object hash mapping key codes to callbacks to be executed when the respective keys are pressed within the body of the grid.  This is typically augmented by calling `addKeyHandler`, but it can also be completely overridden by passing an object hash to the constructor (or otherwise creating one before `Keyboard#postMixInProperties` executes).  The default `keyMap` is exposed via `Keyboard.defaultKeyMap`.
 `headerKeyMap` | Object hash mapping key codes to callbacks to be executed when the respective keys are pressed within the header of the grid.  This is typically augmented by calling `addKeyHandler`, but it can also be completely overridden by passing an object hash to the constructor (or otherwise creating one before `Keyboard#postMixInProperties` executes).  The default `headerKeyMap` is exposed via `Keyboard.defaultHeaderKeyMap`.
+`mouseDownEventType` | `dojo/on` compatible event type. Defaults to `'mousedown'`. Can be overridden to use a different event type to register the mouse down event handler that sets focus. Overridden by `dgrid/extensions/DnD` to `touch.press` (from `dojo/touch`) for compatibility with `dojo/dnd/Source`, which is used by `dgrid/extensions/DnD`.
 
 ### Method Summary
 

extensions/DnD.js

@@ -4,16 +4,16 @@ define([
 	'dojo/_base/array',
 	'dojo/aspect',
 	'dojo/dom-class',
-	'dojo/on',
 	'dojo/topic',
+	'dojo/touch',
 	'dojo/has',
 	'dojo/when',
 	'dojo/dnd/Source',
 	'dojo/dnd/Manager',
 	'dojo/_base/NodeList',
 	'../Selection',
 	'dojo/has!touch?../util/touch'
-], function (declare, lang, arrayUtil, aspect, domClass, on, topic, has, when, DnDSource,
+], function (declare, lang, arrayUtil, aspect, domClass, topic, touch, has, when, DnDSource,
 		DnDManager, NodeList, Selection, touchUtil) {
 	// Requirements
 	// * requires a store (sounds obvious, but not all Lists/Grids have stores...)
@@ -260,6 +260,15 @@ define([
 			this.inherited(arguments);
 			// ensure dndParams is initialized
 			this.dndParams = lang.mixin({ accept: [this.dndSourceType] }, this.dndParams);
+
+			// The DnD extension adds a touch.press listener (via dojo/dnd/Source). In browsers
+			// that support pointer events the presence of this listener prevents dgrid/Keyboard's
+			// 'mousedown' listener from being called. To ensure dgrid/Keyboard works in conjunction
+			// with DnD the mouse down event type for dgrid/Keyboard is changed to touch.press.
+			// Note: this is set in postMixInProperties to ensure it overrides the value in Keyboard
+			// regardless of which module is mixed in first. This means that if you want to override
+			// the value set in DnD you need to do so in the postMixInProperties lifecycle method.
+			this.mouseDownEventType = touch.press;
 		},
 
 		postCreate: function () {