feat(drag-drop): support scrolling parent elements apart from list and viewport (#18082)

Currently for performance reasons we only support scrolling within the drop list itself or the viewport, however in some cases the scrollable container might be different. These changes add a new input that consumers can use to tell the CDK which other parents can be scrolled.

Fixes #18072.
Relates to #13588.

Author: crisbeto

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

@@ -23,7 +23,7 @@ import {
 } from '@angular/core';
 import {TestBed, ComponentFixture, fakeAsync, flush, tick} from '@angular/core/testing';
 import {DOCUMENT} from '@angular/common';
-import {ViewportRuler} from '@angular/cdk/scrolling';
+import {ViewportRuler, ScrollingModule} from '@angular/cdk/scrolling';
 import {_supportsShadowDom} from '@angular/cdk/platform';
 import {of as observableOf} from 'rxjs';
 
@@ -47,7 +47,7 @@ describe('CdkDrag', () => {
       extraDeclarations: Type<any>[] = []): ComponentFixture<T> {
     TestBed
         .configureTestingModule({
-          imports: [DragDropModule],
+          imports: [DragDropModule, ScrollingModule],
           declarations: [componentType, PassthroughComponent, ...extraDeclarations],
           providers: [
             {
@@ -3411,6 +3411,24 @@ describe('CdkDrag', () => {
         cleanup();
       }));
 
+    it('should be able to auto-scroll a parent container', fakeAsync(() => {
+      const fixture = createComponent(DraggableInScrollableParentContainer);
+      fixture.detectChanges();
+      const item = fixture.componentInstance.dragItems.first.element.nativeElement;
+      const container = fixture.nativeElement.querySelector('.container');
+      const containerRect = container.getBoundingClientRect();
+
+      expect(container.scrollTop).toBe(0);
+
+      startDraggingViaMouse(fixture, item);
+      dispatchMouseEvent(document, 'mousemove',
+        containerRect.left + containerRect.width / 2, containerRect.top + containerRect.height);
+      fixture.detectChanges();
+      tickAnimationFrames(20);
+
+      expect(container.scrollTop).toBeGreaterThan(0);
+    }));
+
     it('should pick up descendants inside of containers', fakeAsync(() => {
       const fixture = createComponent(DraggableInDropZoneWithContainer);
       fixture.detectChanges();
@@ -4695,6 +4713,30 @@ class DraggableInScrollableVerticalDropZone extends DraggableInDropZone {
   }
 }
 
+@Component({
+  template: '<div class="container" cdkScrollable>' + DROP_ZONE_FIXTURE_TEMPLATE + '</div>',
+
+  // Note that it needs a margin to ensure that it's not flush against the viewport
+  // edge which will cause the viewport to scroll, rather than the list.
+  styles: [`
+    .container {
+      max-height: 200px;
+      overflow: auto;
+      margin: 10vw 0 0 10vw;
+    }
+  `]
+})
+class DraggableInScrollableParentContainer extends DraggableInDropZone {
+  constructor() {
+    super();
+
+    for (let i = 0; i < 60; i++) {
+      this.items.push({value: `Extra item ${i}`, height: ITEM_HEIGHT, margin: 0});
+    }
+  }
+}
+
+
 @Component({
   // Note that we need the blank `ngSwitch` below to hit the code path that we're testing.
   template: `

src/cdk/drag-drop/directives/drop-list.ts

@@ -22,6 +22,7 @@ import {
   AfterContentInit,
 } from '@angular/core';
 import {Directionality} from '@angular/cdk/bidi';
+import {ScrollDispatcher} from '@angular/cdk/scrolling';
 import {CdkDrag, CDK_DROP_LIST} from './drag';
 import {CdkDragDrop, CdkDragEnter, CdkDragExit, CdkDragSortEvent} from '../drag-events';
 import {CdkDropListGroup} from './drop-list-group';
@@ -148,7 +149,13 @@ export class CdkDropList<T = any> implements AfterContentInit, OnDestroy {
       /** Element that the drop list is attached to. */
       public element: ElementRef<HTMLElement>, dragDrop: DragDrop,
       private _changeDetectorRef: ChangeDetectorRef, @Optional() private _dir?: Directionality,
-      @Optional() @SkipSelf() private _group?: CdkDropListGroup<CdkDropList>) {
+      @Optional() @SkipSelf() private _group?: CdkDropListGroup<CdkDropList>,
+
+      /**
+       * @deprecated _scrollDispatcher parameter to become required.
+       * @breaking-change 11.0.0
+       */
+      private _scrollDispatcher?: ScrollDispatcher) {
     this._dropListRef = dragDrop.createDropList(element);
     this._dropListRef.data = this;
     this._dropListRef.enterPredicate = (drag: DragRef<CdkDrag>, drop: DropListRef<CdkDropList>) => {
@@ -165,6 +172,14 @@ export class CdkDropList<T = any> implements AfterContentInit, OnDestroy {
   }
 
   ngAfterContentInit() {
+    // @breaking-change 11.0.0 Remove null check for _scrollDispatcher once it's required.
+    if (this._scrollDispatcher) {
+      const scrollableParents = this._scrollDispatcher
+        .getAncestorScrollContainers(this.element)
+        .map(scrollable => scrollable.getElementRef().nativeElement);
+      this._dropListRef.withScrollableParents(scrollableParents);
+    }
+
     this._draggables.changes
       .pipe(startWith(this._draggables), takeUntil(this._destroyed))
       .subscribe((items: QueryList<CdkDrag>) => {