feat(drag-drop): add support for multiple handles and handles that are added after init

* Fixes a TODO about supporting handles that are added after init.
* Adds the ability to have more than one handle in a draggable.
* Enables bubbling for the fake mouse events.

Author: crisbeto

src/cdk-experimental/drag-drop/drag.spec.ts

@@ -6,6 +6,7 @@ import {
   ViewChildren,
   QueryList,
   AfterViewInit,
+  ViewEncapsulation,
 } from '@angular/core';
 import {TestBed, ComponentFixture, fakeAsync, flush} from '@angular/core/testing';
 import {DragDropModule} from './drag-drop-module';
@@ -14,6 +15,7 @@ import {CdkDrag} from './drag';
 import {CdkDragDrop} from './drag-events';
 import {moveItemInArray, transferArrayItem} from './drag-utils';
 import {CdkDrop} from './drop';
+import {CdkDragHandle} from './drag-handle';
 
 const ITEM_HEIGHT = 25;
 
@@ -139,6 +141,37 @@ describe('CdkDrag', () => {
       dragElementViaMouse(fixture, handle, 50, 100);
       expect(dragElement.style.transform).toBe('translate3d(50px, 100px, 0px)');
     }));
+
+    it('should be able to use a handle that was added after init', fakeAsync(() => {
+      const fixture = createComponent(StandaloneDraggableWithDelayedHandle);
+
+      fixture.detectChanges();
+      fixture.componentInstance.showHandle = true;
+      fixture.detectChanges();
+
+      const dragElement = fixture.componentInstance.dragElement.nativeElement;
+      const handle = fixture.componentInstance.handleElement.nativeElement;
+
+      expect(dragElement.style.transform).toBeFalsy();
+      dragElementViaMouse(fixture, handle, 50, 100);
+      expect(dragElement.style.transform).toBe('translate3d(50px, 100px, 0px)');
+    }));
+
+    it('should be able to use more than one handle to drag the element', fakeAsync(() => {
+      const fixture = createComponent(StandaloneDraggableWithMultipleHandles);
+      fixture.detectChanges();
+
+      const dragElement = fixture.componentInstance.dragElement.nativeElement;
+      const handles = fixture.componentInstance.handles.map(handle => handle.element.nativeElement);
+
+      expect(dragElement.style.transform).toBeFalsy();
+      dragElementViaMouse(fixture, handles[1], 50, 100);
+      expect(dragElement.style.transform).toBe('translate3d(50px, 100px, 0px)');
+
+      dragElementViaMouse(fixture, handles[0], 100, 200);
+      expect(dragElement.style.transform).toBe('translate3d(150px, 300px, 0px)');
+    }));
+
   });
 
   describe('in a drop container', () => {
@@ -415,9 +448,48 @@ export class StandaloneDraggable {
 export class StandaloneDraggableWithHandle {
   @ViewChild('dragElement') dragElement: ElementRef<HTMLElement>;
   @ViewChild('handleElement') handleElement: ElementRef<HTMLElement>;
-  @ViewChild(CdkDrag) dragInstance: CdkDrag;
 }
 
+@Component({
+  template: `
+    <div #dragElement cdkDrag
+      style="width: 100px; height: 100px; background: red; position: relative">
+      <div
+        #handleElement
+        *ngIf="showHandle"
+        cdkDragHandle style="width: 10px; height: 10px; background: green;"></div>
+    </div>
+  `
+})
+export class StandaloneDraggableWithDelayedHandle {
+  @ViewChild('dragElement') dragElement: ElementRef<HTMLElement>;
+  @ViewChild('handleElement') handleElement: ElementRef<HTMLElement>;
+  showHandle = false;
+}
+
+@Component({
+  encapsulation: ViewEncapsulation.None,
+  styles: [`
+    .cdk-drag-handle {
+      position: absolute;
+      top: 0;
+      background: green;
+      width: 10px;
+      height: 10px;
+    }
+  `],
+  template: `
+    <div #dragElement cdkDrag
+      style="width: 100px; height: 100px; background: red; position: relative">
+      <div cdkDragHandle style="left: 0;"></div>
+      <div cdkDragHandle style="right: 0;"></div>
+    </div>
+  `
+})
+export class StandaloneDraggableWithMultipleHandles {
+  @ViewChild('dragElement') dragElement: ElementRef<HTMLElement>;
+  @ViewChildren(CdkDragHandle) handles: QueryList<CdkDragHandle>;
+}
 
 @Component({
   template: `

src/cdk-experimental/drag-drop/drag.ts

@@ -20,6 +20,8 @@ import {
   EventEmitter,
   ViewContainerRef,
   EmbeddedViewRef,
+  ContentChildren,
+  QueryList,
 } from '@angular/core';
 import {CdkDragHandle} from './drag-handle';
 import {DOCUMENT} from '@angular/platform-browser';
@@ -41,6 +43,8 @@ const activeEventOptions = supportsPassiveEventListeners() ? {passive: false} :
   exportAs: 'cdkDrag',
   host: {
     'class': 'cdk-drag',
+    '(mousedown)': '_startDragging($event)',
+    '(touchstart)': '_startDragging($event)',
   }
 })
 export class CdkDrag implements AfterContentInit, OnDestroy {
@@ -84,8 +88,8 @@ export class CdkDrag implements AfterContentInit, OnDestroy {
   /** Drop container in which the CdkDrag resided when dragging began. */
   private _initialContainer: CdkDropContainer;
 
-  /** Element that can be used to drag the draggable item. */
-  @ContentChild(CdkDragHandle) _handle: CdkDragHandle;
+  /** Elements that can be used to drag the draggable item. */
+  @ContentChildren(CdkDragHandle) _handles: QueryList<CdkDragHandle>;
 
   /** Element that will be used as a template to create the draggable item's preview. */
   @ContentChild(CdkDragPreview) _previewTemplate: CdkDragPreview;
@@ -130,11 +134,6 @@ export class CdkDrag implements AfterContentInit, OnDestroy {
   }
 
   ngAfterContentInit() {
-    // TODO: doesn't handle (pun intended) the handle being destroyed
-    const dragElement = (this._handle ? this._handle.element : this.element).nativeElement;
-    dragElement.addEventListener('mousedown', this._pointerDown);
-    dragElement.addEventListener('touchstart', this._pointerDown);
-
     // Webkit won't preventDefault on a dynamically-added `touchmove` listener, which means that
     // we need to add one ahead of time. See https://bugs.webkit.org/show_bug.cgi?id=184250.
     // TODO: move into a central registry.
@@ -157,8 +156,27 @@ export class CdkDrag implements AfterContentInit, OnDestroy {
     }
   }
 
+  /** Starts the dragging sequence. */
+  _startDragging(event: MouseEvent | TouchEvent) {
+    // Delegate the event based on whether it started from a handle or the element itself.
+    if (this._handles.length) {
+      const targetHandle = this._handles.find(handle => {
+        const element = handle.element.nativeElement;
+        const target = event.target;
+        return !!target && (target === element || element.contains(target as HTMLElement));
+      });
+
+      if (targetHandle) {
+        this._pointerDown(targetHandle.element, event);
+      }
+    } else {
+      this._pointerDown(this.element, event);
+    }
+  }
+
   /** Handler for when the pointer is pressed down on the element or the handle. */
-  private _pointerDown = (event: MouseEvent | TouchEvent) => {
+  private _pointerDown = (referenceElement: ElementRef<HTMLElement>,
+                          event: MouseEvent | TouchEvent) => {
     if (this._isDragging) {
       return;
     }
@@ -169,7 +187,7 @@ export class CdkDrag implements AfterContentInit, OnDestroy {
     // If we have a custom preview template, the element won't be visible anyway so we avoid the
     // extra `getBoundingClientRect` calls and just move the preview next to the cursor.
     this._pickupPositionInElement = this._previewTemplate ? {x: 0, y: 0} :
-        this._getPointerPositionInElement(event);
+        this._getPointerPositionInElement(referenceElement, event);
     this._pickupPositionOnPage = this._getPointerPositionOnPage(event);
     this._registerMoveListeners(event);
 
@@ -365,11 +383,13 @@ export class CdkDrag implements AfterContentInit, OnDestroy {
 
   /**
    * Figures out the coordinates at which an element was picked up.
+   * @param referenceElement Element that initiated the dragging.
    * @param event Event that initiated the dragging.
    */
-  private _getPointerPositionInElement(event: MouseEvent | TouchEvent): Point {
+  private _getPointerPositionInElement(referenceElement: ElementRef<HTMLElement>,
+                                       event: MouseEvent | TouchEvent): Point {
     const elementRect = this.element.nativeElement.getBoundingClientRect();
-    const handleElement = this._handle ? this._handle.element.nativeElement : null;
+    const handleElement = referenceElement === this.element ? null : referenceElement.nativeElement;
     const referenceRect = handleElement ? handleElement.getBoundingClientRect() : elementRect;
     const x = this._isTouchEvent(event) ? event.targetTouches[0].pageX - referenceRect.left :
                                           event.offsetX;

src/cdk/testing/event-objects.ts

@@ -11,7 +11,7 @@ export function createMouseEvent(type: string, x = 0, y = 0) {
   const event = document.createEvent('MouseEvent');
 
   event.initMouseEvent(type,
-    false, /* canBubble */
+    true, /* canBubble */
     false, /* cancelable */
     window, /* view */
     0, /* detail */