Fix targetTouches/changedTouches mismatch and multitouch bugs.

Fixes #159, #118

lib/DraggableCore.es6

@@ -1,6 +1,6 @@
 // @flow
 import React, {PropTypes} from 'react';
-import {matchesSelector, addEvent, removeEvent, addUserSelectStyles,
+import {matchesSelector, addEvent, removeEvent, addUserSelectStyles, getTouchIdentifier,
         removeUserSelectStyles, styleHacks} from './utils/domFns';
 import {createCoreData, getControlPosition, snapToGrid} from './utils/positionFns';
 import {dontSetMe} from './utils/shims';
@@ -29,7 +29,7 @@ type CoreState = {
   dragging: boolean,
   lastX: number,
   lastY: number,
-  touchIdentifier: number
+  touchIdentifier: ?number
 };
 
 //
@@ -164,7 +164,7 @@ export default class DraggableCore extends React.Component {
     dragging: false,
     // Used while dragging to determine deltas.
     lastX: NaN, lastY: NaN,
-    touchIdentifier: NaN
+    touchIdentifier: null
   };
 
   componentWillUnmount() {
@@ -195,12 +195,13 @@ export default class DraggableCore extends React.Component {
     // Set touch identifier in component state if this is a touch event. This allows us to
     // distinguish between individual touches on multitouch screens by identifying which
     // touchpoint was set to this element.
-    if (e.targetTouches){
-      this.setState({touchIdentifier: e.targetTouches[0].identifier});
-    }
+    const touchIdentifier = getTouchIdentifier(e);
+    this.setState({touchIdentifier});
 
     // Get the current drag point from the event. This is used as the offset.
-    const {x, y} = getControlPosition(e, this);
+    const position = getControlPosition(e, touchIdentifier, this);
+    if (position == null) return; // not possible but satisfies flow
+    const {x, y} = position;
 
     // Create an event object with all the data parents need to make a decision here.
     const coreEvent = createCoreData(this, x, y);
@@ -234,12 +235,15 @@ export default class DraggableCore extends React.Component {
   };
 
   handleDrag: EventHandler<MouseEvent> = (e) => {
-    // Return if this is a touch event, but not the correct one for this element
-    if (e.targetTouches && (e.targetTouches[0].identifier !== this.state.touchIdentifier)) return;
 
-    let {x, y} = getControlPosition(e, this);
+    // Get the current drag point from the event. This is used as the offset.
+    const position = getControlPosition(e, this.state.touchIdentifier, this);
+    if (position == null) return;
+    let {x, y} = position;
 
     // Snap to grid if prop has been provided
+    if (x !== x) debugger;
+
     if (Array.isArray(this.props.grid)) {
       let deltaX = x - this.state.lastX, deltaY = y - this.state.lastY;
       [deltaX, deltaY] = snapToGrid(this.props.grid, deltaX, deltaY);
@@ -267,16 +271,14 @@ export default class DraggableCore extends React.Component {
   handleDragStop: EventHandler<MouseEvent> = (e) => {
     if (!this.state.dragging) return;
 
-    // Short circuit if this is not the correct touch event. `changedTouches` contains all
-    // touch points that have been removed from the surface.
-    if (e.changedTouches && (e.changedTouches[0].identifier !== this.state.touchIdentifier)) return;
+    const position = getControlPosition(e, this.state.touchIdentifier, this);
+    if (position == null) return;
+    const {x, y} = position;
+    const coreEvent = createCoreData(this, x, y);
 
     // Remove user-select hack
     if (this.props.enableUserSelectHack) removeUserSelectStyles();
 
-    const {x, y} = getControlPosition(e, this);
-    const coreEvent = createCoreData(this, x, y);
-
     log('DraggableCore: handleDragStop: %j', coreEvent);
 
     // Reset the el.

lib/utils/domFns.es6

@@ -83,9 +83,7 @@ export function innerWidth(node: HTMLElement): number {
 }
 
 // Get from offsetParent
-export function offsetXYFromParentOf(e: MouseEvent, node: HTMLElement & {offsetParent: HTMLElement}): ControlPosition {
-  const evt = e.targetTouches ? e.targetTouches[0] : e;
-
+export function offsetXYFromParentOf(evt: {clientX: number, clientY: number}, node: HTMLElement & {offsetParent: HTMLElement}): ControlPosition {
   const offsetParent = node.offsetParent || document.body;
   const offsetParentRect = node.offsetParent === document.body ? {left: 0, top: 0} : offsetParent.getBoundingClientRect();
 
@@ -104,6 +102,16 @@ export function createSVGTransform({x, y}: {x: number, y: number}): string {
   return 'translate(' + x + ',' + y + ')';
 }
 
+export function getTouch(e: MouseEvent, identifier: number): ?{clientX: number, clientY: number} {
+  return (e.targetTouches && findInArray(e.targetTouches, t => identifier === t.identifier)) ||
+         (e.changedTouches && findInArray(e.changedTouches, t => identifier === t.identifier));
+}
+
+export function getTouchIdentifier(e: MouseEvent): ?number {
+  if (e.targetTouches && e.targetTouches[0]) return e.targetTouches[0].identifier;
+  if (e.changedTouches && e.changedTouches[0]) return e.changedTouches[0].identifier;
+}
+
 // User-select Hacks:
 //
 // Useful for preventing blue highlights all over everything when dragging.

lib/utils/positionFns.es6

@@ -1,7 +1,7 @@
 // @flow
 import {isNum, int} from './shims';
 import ReactDOM from 'react-dom';
-import {innerWidth, innerHeight, offsetXYFromParentOf, outerWidth, outerHeight} from './domFns';
+import {getTouch, innerWidth, innerHeight, offsetXYFromParentOf, outerWidth, outerHeight} from './domFns';
 
 import type Draggable from '../Draggable';
 import type {Bounds, ControlPosition, DraggableData} from './types';
@@ -63,8 +63,10 @@ export function canDragY(draggable: Draggable): boolean {
 }
 
 // Get {x, y} positions from event.
-export function getControlPosition(e: MouseEvent, draggableCore: DraggableCore): ControlPosition {
-  return offsetXYFromParentOf(e, ReactDOM.findDOMNode(draggableCore));
+export function getControlPosition(e: MouseEvent, touchIdentifier: ?number, draggableCore: DraggableCore): ?ControlPosition {
+  const touchObj = typeof touchIdentifier === 'number' ? getTouch(e, touchIdentifier) : null;
+  if (typeof touchIdentifier === 'number' && !touchObj) return null; // not the right touch
+  return offsetXYFromParentOf(touchObj || e, ReactDOM.findDOMNode(draggableCore));
 }
 
 // Create an data object exposed by <DraggableCore>'s events