fix(drag-drop): prevent mouse wheel scrolling while dragging

Prevents users from scrolling using the mouse wheel while an item is being dragged. This is a temporary measure until we have a solution to auto-scrolling while dragging, as well as to avoid having to measure the page for every pixel that the user has dragged.

Fixes #13508.

Author: crisbeto

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

@@ -5,6 +5,7 @@ import {
   dispatchMouseEvent,
   createTouchEvent,
   dispatchTouchEvent,
+  dispatchFakeEvent,
 } from '@angular/cdk/testing';
 import {DragDropRegistry} from './drag-drop-registry';
 import {DragDropModule} from './drag-drop-module';
@@ -192,6 +193,15 @@ describe('DragDropRegistry', () => {
     expect(event.defaultPrevented).toBe(true);
   });
 
+  it('should not prevent the default `wheel` actions when nothing is being dragged', () => {
+    expect(dispatchFakeEvent(document, 'wheel').defaultPrevented).toBe(false);
+  });
+
+  it('should prevent the default `wheel` action when an item is being dragged', () => {
+    registry.startDragging(testComponent.dragItems.first, createMouseEvent('mousedown'));
+    expect(dispatchFakeEvent(document, 'wheel').defaultPrevented).toBe(true);
+  });
+
 });
 
 @Component({

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

@@ -43,7 +43,7 @@ export class DragDropRegistry<I, C extends {id: string}> implements OnDestroy {
   private _activeDragInstances = new Set<I>();
 
   /** Keeps track of the event listeners that we've bound to the `document`. */
-  private _globalListeners = new Map<'touchmove' | 'mousemove' | 'touchend' | 'mouseup', {
+  private _globalListeners = new Map<'touchmove' | 'mousemove' | 'touchend' | 'mouseup' | 'wheel', {
     handler: PointerEventHandler,
     options?: AddEventListenerOptions | boolean
   }>();
@@ -81,10 +81,13 @@ export class DragDropRegistry<I, C extends {id: string}> implements OnDestroy {
   registerDragItem(drag: I) {
     this._dragInstances.add(drag);
 
+    // The `touchmove` event gets bound once, ahead of time, because WebKit
+    // won't preventDefault on a dynamically-added `touchmove` listener.
+    // See https://bugs.webkit.org/show_bug.cgi?id=184250.
     if (this._dragInstances.size === 1) {
       this._ngZone.runOutsideAngular(() => {
-        // The event handler has to be explicitly active, because
-        // newer browsers make it passive by default.
+        // The event handler has to be explicitly active,
+        // because newer browsers make it passive by default.
         this._document.addEventListener('touchmove', this._preventScrollListener,
             activeCapturingEventOptions);
       });
@@ -135,12 +138,22 @@ export class DragDropRegistry<I, C extends {id: string}> implements OnDestroy {
         .set(upEvent, {
           handler: e => this.pointerUp.next(e),
           options: true
-        })
-        .forEach((config, name) => {
-          this._ngZone.runOutsideAngular(() => {
-            this._document.addEventListener(name, config.handler, config.options);
-          });
         });
+
+      // TODO(crisbeto): prevent mouse wheel scrolling while
+      // dragging until we've set up proper scroll handling.
+      if (!isTouchEvent) {
+        this._globalListeners.set('wheel', {
+          handler: this._preventScrollListener,
+          options: activeCapturingEventOptions
+        });
+      }
+
+      this._ngZone.runOutsideAngular(() => {
+        this._globalListeners.forEach((config, name) => {
+          this._document.addEventListener(name, config.handler, config.options);
+        });
+      });
     }
   }
 
@@ -173,11 +186,9 @@ export class DragDropRegistry<I, C extends {id: string}> implements OnDestroy {
   }
 
   /**
-   * Listener used to prevent `touchmove` events while the element is being dragged.
-   * This gets bound once, ahead of time, because WebKit won't preventDefault on a
-   * dynamically-added `touchmove` listener. See https://bugs.webkit.org/show_bug.cgi?id=184250.
+   * Listener used to prevent `touchmove` and `wheel` events while the element is being dragged.
    */
-  private _preventScrollListener = (event: TouchEvent) => {
+  private _preventScrollListener = (event: Event) => {
     if (this._activeDragInstances.size) {
       event.preventDefault();
     }