feat(drag-drop): add service for attaching drag&drop to arbitrary DOM nodes

* Adds the  `DragDrop` service that simplifies the construction logic for `DragRef` and `DropListRef` and allows consumers to attach drag&drop functionality to arbitrary DOM nodes, rather than having to go through the directives.
* Reworks `DragRef` and `DragDropRef` to make them easier to construct.
* Normalizes some of the instances where some parameters only accept an `ElementRef`, whereas others accept `ElementRef | HTMLElement`.

Author: crisbeto

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

@@ -21,6 +21,7 @@ import {
   createTouchEvent,
 } from '@angular/cdk/testing';
 import {Directionality} from '@angular/cdk/bidi';
+import {of as observableOf} from 'rxjs';
 import {CdkDrag, CDK_DRAG_CONFIG} from './drag';
 import {CdkDragDrop} from '../drag-events';
 import {moveItemInArray} from '../drag-utils';
@@ -1082,7 +1083,7 @@ describe('CdkDrag', () => {
     it('should dispatch the correct `dropped` event in RTL horizontal drop zone', fakeAsync(() => {
       const fixture = createComponent(DraggableInHorizontalDropZone, [{
         provide: Directionality,
-        useValue: ({value: 'rtl'})
+        useValue: ({value: 'rtl', change: observableOf()})
       }]);
 
       fixture.nativeElement.setAttribute('dir', 'rtl');
@@ -1238,7 +1239,7 @@ describe('CdkDrag', () => {
     it('should pass the proper direction to the preview in rtl', fakeAsync(() => {
       const fixture = createComponent(DraggableInDropZone, [{
         provide: Directionality,
-        useValue: ({value: 'rtl'})
+        useValue: ({value: 'rtl', change: observableOf()})
       }]);
 
       fixture.detectChanges();

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

@@ -50,6 +50,7 @@ import {CDK_DRAG_PARENT} from '../drag-parent';
 import {DragRef, DragRefConfig} from '../drag-ref';
 import {DropListRef} from '../drop-list-ref';
 import {CdkDropListInternal as CdkDropList} from './drop-list';
+import {DragDrop} from '../drag-drop';
 
 /** Injection token that can be used to configure the behavior of `CdkDrag`. */
 export const CDK_DRAG_CONFIG = new InjectionToken<DragRefConfig>('CDK_DRAG_CONFIG', {
@@ -168,27 +169,52 @@ export class CdkDrag<T = any> implements AfterViewInit, OnChanges, OnDestroy {
     @Inject(DOCUMENT) private _document: any,
     private _ngZone: NgZone,
     private _viewContainerRef: ViewContainerRef,
-    private _viewportRuler: ViewportRuler,
-    private _dragDropRegistry: DragDropRegistry<DragRef, DropListRef>,
-    @Inject(CDK_DRAG_CONFIG) private _config: DragRefConfig,
-    @Optional() private _dir: Directionality) {
-
-    const ref = this._dragRef = new DragRef(element, this._document, this._ngZone,
-      this._viewContainerRef, this._viewportRuler, this._dragDropRegistry,
-      this._config, this.dropContainer ? this.dropContainer._dropListRef : undefined,
-      this._dir);
-    ref.data = this;
-    ref.beforeStarted.subscribe(() => {
+    viewportRuler: ViewportRuler,
+    dragDropRegistry: DragDropRegistry<DragRef, DropListRef>,
+    @Inject(CDK_DRAG_CONFIG) config: DragRefConfig,
+    @Optional() dir: Directionality,
+
+    /**
+     * @deprecated `viewportRuler` and `dragDropRegistry` parameters
+     * to be removed. Also `dragDrop` parameter to be made required.
+     * @breaking-change 8.0.0.
+     */
+    dragDrop?: DragDrop) {
+
+    // @breaking-change 8.0.0 Remove null check once the paramter is made required.
+    if (dragDrop) {
+      this._dragRef = dragDrop.createDrag(element, config);
+    } else {
+      this._dragRef = new DragRef(element, config, _document, _ngZone, viewportRuler,
+          dragDropRegistry);
+    }
+
+    this._dragRef.data = this;
+    this._dragRef.beforeStarted.subscribe(() => {
+      const ref = this._dragRef;
+
       if (!ref.isDragging()) {
         ref.disabled = this.disabled;
         ref.lockAxis = this.lockAxis;
         ref
           .withBoundaryElement(this._getBoundaryElement())
-          .withPlaceholderTemplate(this._placeholderTemplate)
-          .withPreviewTemplate(this._previewTemplate);
+          .withPlaceholderTemplate(this._placeholderTemplate ? {
+            templateRef: this._placeholderTemplate.templateRef,
+            data: this._placeholderTemplate.data,
+            viewContainer: this._viewContainerRef
+          } : null)
+          .withPreviewTemplate(this._previewTemplate ? {
+            templateRef: this._previewTemplate.templateRef,
+            data: this._previewTemplate.data,
+            viewContainer: this._viewContainerRef
+          } : null);
+
+        if (dir) {
+          ref.withDirection(dir.value);
+        }
       }
     });
-    this._proxyEvents(ref);
+    this._proxyEvents(this._dragRef);
   }
 
   /**

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

@@ -21,6 +21,7 @@ import {
   ChangeDetectorRef,
   SkipSelf,
   Inject,
+  AfterContentInit,
 } from '@angular/core';
 import {DOCUMENT} from '@angular/common';
 import {Directionality} from '@angular/cdk/bidi';
@@ -31,6 +32,9 @@ import {CDK_DROP_LIST_CONTAINER, CdkDropListContainer} from '../drop-list-contai
 import {CdkDropListGroup} from './drop-list-group';
 import {DropListRef} from '../drop-list-ref';
 import {DragRef} from '../drag-ref';
+import {DragDrop} from '../drag-drop';
+import {Subject} from 'rxjs';
+import {startWith, takeUntil} from 'rxjs/operators';
 
 /** Counter used to generate unique ids for drop zones. */
 let _uniqueIdCounter = 0;
@@ -62,15 +66,22 @@ export interface CdkDropListInternal extends CdkDropList {}
     '[class.cdk-drop-list-receiving]': '_dropListRef.isReceiving()',
   }
 })
-export class CdkDropList<T = any> implements CdkDropListContainer, OnDestroy {
+export class CdkDropList<T = any> implements CdkDropListContainer, AfterContentInit, OnDestroy {
+  /** Emits when the list has been destroyed. */
+  private _destroyed = new Subject<void>();
+
   /** Keeps track of the drop lists that are currently on the page. */
   private static _dropLists: CdkDropList[] = [];
 
   /** Reference to the underlying drop list instance. */
   _dropListRef: DropListRef<CdkDropList<T>>;
 
   /** Draggable items in the container. */
-  @ContentChildren(forwardRef(() => CdkDrag)) _draggables: QueryList<CdkDrag>;
+  @ContentChildren(forwardRef(() => CdkDrag), {
+    // Explicitly set to false since some of the logic below makes assumptions about it.
+    // The `.withItems` call below should be updated if we ever need to switch this to `true`.
+    descendants: false
+  }) _draggables: QueryList<CdkDrag>;
 
   /**
    * Other draggable containers that this container is connected to and into which the
@@ -134,34 +145,51 @@ export class CdkDropList<T = any> implements CdkDropListContainer, OnDestroy {
   sorted: EventEmitter<CdkDragSortEvent<T>> = new EventEmitter<CdkDragSortEvent<T>>();
 
   constructor(
+    /** Element that the drop list is attached to. */
     public element: ElementRef<HTMLElement>,
     dragDropRegistry: DragDropRegistry<DragRef, DropListRef>,
     private _changeDetectorRef: ChangeDetectorRef,
-    @Optional() dir?: Directionality,
+    @Optional() private _dir?: Directionality,
     @Optional() @SkipSelf() private _group?: CdkDropListGroup<CdkDropList>,
-    // @breaking-change 8.0.0 `_document` parameter to be made required.
-    @Optional() @Inject(DOCUMENT) _document?: any) {
-
+    @Optional() @Inject(DOCUMENT) _document?: any,
+
+    /**
+     * @deprecated `dragDropRegistry` and `_document` parameters to be removed.
+     * Also `dragDrop` parameter to be made required.
+     * @breaking-change 8.0.0.
+     */
+    dragDrop?: DragDrop) {
+
+    // @breaking-change 8.0.0 Remove null check once `dragDrop` parameter is made required.
+    if (dragDrop) {
+      this._dropListRef = dragDrop.createDropList(element);
+    } else {
+      this._dropListRef = new DropListRef(element, dragDropRegistry, _document || document);
+    }
 
-    // @breaking-change 8.0.0 Remove || once `_document` parameter is required.
-    const ref = this._dropListRef = new DropListRef(element, dragDropRegistry,
-        _document || document, dir);
-    ref.data = this;
-    ref.enterPredicate = (drag: DragRef<CdkDrag>, drop: DropListRef<CdkDropList>) => {
+    this._dropListRef.data = this;
+    this._dropListRef.enterPredicate = (drag: DragRef<CdkDrag>, drop: DropListRef<CdkDropList>) => {
       return this.enterPredicate(drag.data, drop.data);
     };
-    this._syncInputs(ref);
-    this._proxyEvents(ref);
+    this._syncInputs(this._dropListRef);
+    this._proxyEvents(this._dropListRef);
     CdkDropList._dropLists.push(this);
 
     if (_group) {
       _group._items.add(this);
     }
   }
 
+  ngAfterContentInit() {
+    this._draggables.changes
+      .pipe(startWith(this._draggables), takeUntil(this._destroyed))
+      .subscribe((items: QueryList<CdkDrag>) => {
+        this._dropListRef.withItems(items.map(drag => drag._dragRef));
+      });
+  }
+
   ngOnDestroy() {
     const index = CdkDropList._dropLists.indexOf(this);
-    this._dropListRef.dispose();
 
     if (index > -1) {
       CdkDropList._dropLists.splice(index, 1);
@@ -170,6 +198,10 @@ export class CdkDropList<T = any> implements CdkDropListContainer, OnDestroy {
     if (this._group) {
       this._group._items.delete(this);
     }
+
+    this._dropListRef.dispose();
+    this._destroyed.next();
+    this._destroyed.complete();
   }
 
   /** Starts dragging an item. */
@@ -253,6 +285,12 @@ export class CdkDropList<T = any> implements CdkDropListContainer, OnDestroy {
 
   /** Syncs the inputs of the CdkDropList with the options of the underlying DropListRef. */
   private _syncInputs(ref: DropListRef<CdkDropList>) {
+    if (this._dir) {
+      this._dir.change
+        .pipe(startWith(this._dir.value), takeUntil(this._destroyed))
+        .subscribe(value => ref.withDirection(value));
+    }
+
     ref.beforeStarted.subscribe(() => {
       const siblings = coerceArray(this.connectedTo).map(drop => {
         return typeof drop === 'string' ?
@@ -270,8 +308,7 @@ export class CdkDropList<T = any> implements CdkDropListContainer, OnDestroy {
       ref.lockAxis = this.lockAxis;
       ref
         .connectedTo(siblings.filter(drop => drop && drop !== this).map(list => list._dropListRef))
-        .withOrientation(this.orientation)
-        .withItems(this._draggables.map(drag => drag._dragRef));
+        .withOrientation(this.orientation);
     });
   }
 

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

@@ -13,6 +13,7 @@ import {CdkDrag} from './directives/drag';
 import {CdkDragHandle} from './directives/drag-handle';
 import {CdkDragPreview} from './directives/drag-preview';
 import {CdkDragPlaceholder} from './directives/drag-placeholder';
+import {DragDrop} from './drag-drop';
 
 @NgModule({
   declarations: [
@@ -31,5 +32,8 @@ import {CdkDragPlaceholder} from './directives/drag-placeholder';
     CdkDragPreview,
     CdkDragPlaceholder,
   ],
+  providers: [
+    DragDrop,
+  ]
 })
 export class DragDropModule {}

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

@@ -0,0 +1,49 @@
+/**
+ * @license
+ * Copyright Google LLC All Rights Reserved.
+ *
+ * Use of this source code is governed by an MIT-style license that can be
+ * found in the LICENSE file at https://angular.io/license
+ */
+
+import {Injectable, Inject, NgZone, ElementRef} from '@angular/core';
+import {DOCUMENT} from '@angular/common';
+import {ViewportRuler} from '@angular/cdk/scrolling';
+import {DragRef, DragRefConfig} from './drag-ref';
+import {DropListRef} from './drop-list-ref';
+import {DragDropRegistry} from './drag-drop-registry';
+
+/**
+ * Service that allows for drag&drop functionality to be attached to DOM elements.
+ */
+@Injectable({providedIn: 'root'})
+export class DragDrop {
+  constructor(
+    @Inject(DOCUMENT) private _document: any,
+    private _ngZone: NgZone,
+    private _viewportRuler: ViewportRuler,
+    private _dragDropRegistry: DragDropRegistry<DragRef, DropListRef>) {}
+
+  /**
+   * Turns an element into a draggable item.
+   * @param element Element to which to attach the dragging functionality.
+   * @param config Object used to configure the dragging behavior.
+   */
+  createDrag<T = any>(element: ElementRef<HTMLElement> | HTMLElement,
+                config: DragRefConfig = {
+                  dragStartThreshold: 5,
+                  pointerDirectionChangeThreshold: 5
+                }): DragRef<T> {
+
+    return new DragRef<T>(element, config, this._document, this._ngZone, this._viewportRuler,
+        this._dragDropRegistry);
+  }
+
+  /**
+   * Turns an element into a drop list.
+   * @param element Element to which to attach the drop list functionality.
+   */
+  createDropList<T = any>(element: ElementRef<HTMLElement> | HTMLElement): DropListRef<T> {
+    return new DropListRef<T>(element, this._dragDropRegistry, this._document);
+  }
+}