feat(drag-drop): indicate in dropped event whether item was dropped outside of container

Adds an extra flag on the `CdkDragDrop` event that indicates whether the user's pointer was over the container when they dropped an item.

Fixes #14136.

Author: crisbeto

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

@@ -53,6 +53,8 @@ export interface CdkDragDrop<T, O = T> {
   container: CdkDropListContainer<T>;
   /** Container from which the item was picked up. Can be the same as the `container`. */
   previousContainer: CdkDropListContainer<O>;
+  /** Whether the user's pointer was over the container when the item was dropped. */
+  isPointerOverContainer: boolean;
 }
 
 /** Event emitted as the user is dragging a draggable item. */

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

@@ -765,13 +765,55 @@ describe('CdkDrag', () => {
         currentIndex: 2,
         item: firstItem,
         container: fixture.componentInstance.dropInstance,
-        previousContainer: fixture.componentInstance.dropInstance
+        previousContainer: fixture.componentInstance.dropInstance,
+        isPointerOverContainer: true
       });
 
       expect(dragItems.map(drag => drag.element.nativeElement.textContent!.trim()))
           .toEqual(['One', 'Two', 'Zero', 'Three']);
     }));
 
+    it('should expose whether an item was dropped over a container', fakeAsync(() => {
+      const fixture = createComponent(DraggableInDropZone);
+      fixture.detectChanges();
+      const dragItems = fixture.componentInstance.dragItems;
+      const firstItem = dragItems.first;
+      const thirdItemRect = dragItems.toArray()[2].element.nativeElement.getBoundingClientRect();
+
+      dragElementViaMouse(fixture, firstItem.element.nativeElement,
+          thirdItemRect.left + 1, thirdItemRect.top + 1);
+      flush();
+      fixture.detectChanges();
+
+      expect(fixture.componentInstance.droppedSpy).toHaveBeenCalledTimes(1);
+
+      const event: CdkDragDrop<any> =
+          fixture.componentInstance.droppedSpy.calls.mostRecent().args[0];
+
+      expect(event.isPointerOverContainer).toBe(true);
+    }));
+
+    it('should expose whether an item was dropped outside of a container', fakeAsync(() => {
+      const fixture = createComponent(DraggableInDropZone);
+      fixture.detectChanges();
+      const dragItems = fixture.componentInstance.dragItems;
+      const firstItem = dragItems.first;
+      const containerRect = fixture.componentInstance.dropInstance.element
+          .nativeElement.getBoundingClientRect();
+
+      dragElementViaMouse(fixture, firstItem.element.nativeElement,
+          containerRect.right + 10, containerRect.bottom + 10);
+      flush();
+      fixture.detectChanges();
+
+      expect(fixture.componentInstance.droppedSpy).toHaveBeenCalledTimes(1);
+
+      const event: CdkDragDrop<any> =
+          fixture.componentInstance.droppedSpy.calls.mostRecent().args[0];
+
+      expect(event.isPointerOverContainer).toBe(false);
+    }));
+
     it('should dispatch the `sorted` event as an item is being sorted', fakeAsync(() => {
       const fixture = createComponent(DraggableInDropZone);
       fixture.detectChanges();
@@ -830,7 +872,8 @@ describe('CdkDrag', () => {
         currentIndex: 0,
         item: firstItem,
         container: fixture.componentInstance.dropInstance,
-        previousContainer: fixture.componentInstance.dropInstance
+        previousContainer: fixture.componentInstance.dropInstance,
+        isPointerOverContainer: false
       });
 
       expect(dragItems.map(drag => drag.element.nativeElement.textContent!.trim()))
@@ -887,7 +930,8 @@ describe('CdkDrag', () => {
         currentIndex: 2,
         item: firstItem,
         container: fixture.componentInstance.dropInstance,
-        previousContainer: fixture.componentInstance.dropInstance
+        previousContainer: fixture.componentInstance.dropInstance,
+        isPointerOverContainer: true
       });
 
       expect(dragItems.map(drag => drag.element.nativeElement.textContent!.trim()))
@@ -926,7 +970,8 @@ describe('CdkDrag', () => {
         currentIndex: 2,
         item: firstItem,
         container: fixture.componentInstance.dropInstance,
-        previousContainer: fixture.componentInstance.dropInstance
+        previousContainer: fixture.componentInstance.dropInstance,
+        isPointerOverContainer: true
       });
 
       expect(dragItems.map(drag => drag.element.nativeElement.textContent!.trim()))
@@ -961,7 +1006,8 @@ describe('CdkDrag', () => {
         currentIndex: 0,
         item: firstItem,
         container: fixture.componentInstance.dropInstance,
-        previousContainer: fixture.componentInstance.dropInstance
+        previousContainer: fixture.componentInstance.dropInstance,
+        isPointerOverContainer: false
       });
 
       expect(dragItems.map(drag => drag.element.nativeElement.textContent!.trim()))
@@ -1797,7 +1843,8 @@ describe('CdkDrag', () => {
           currentIndex: 3,
           item,
           container: fixture.componentInstance.dropInstances.toArray()[1],
-          previousContainer: fixture.componentInstance.dropInstances.first
+          previousContainer: fixture.componentInstance.dropInstances.first,
+          isPointerOverContainer: true
         });
       }));
 
@@ -1898,7 +1945,8 @@ describe('CdkDrag', () => {
         currentIndex: 3,
         item: groups[0][1],
         container: dropInstances[1],
-        previousContainer: dropInstances[0]
+        previousContainer: dropInstances[0],
+        isPointerOverContainer: true
       });
     }));
 
@@ -1927,7 +1975,8 @@ describe('CdkDrag', () => {
           currentIndex: 1,
           item: groups[0][1],
           container: dropInstances[0],
-          previousContainer: dropInstances[0]
+          previousContainer: dropInstances[0],
+          isPointerOverContainer: false
         });
       }));
 
@@ -1956,7 +2005,8 @@ describe('CdkDrag', () => {
           currentIndex: 1,
           item: groups[0][1],
           container: dropInstances[0],
-          previousContainer: dropInstances[0]
+          previousContainer: dropInstances[0],
+          isPointerOverContainer: false
         });
       }));
 
@@ -2078,7 +2128,8 @@ describe('CdkDrag', () => {
         currentIndex: 3,
         item: groups[0][1],
         container: dropInstances[1],
-        previousContainer: dropInstances[0]
+        previousContainer: dropInstances[0],
+        isPointerOverContainer: true
       });
     }));
 
@@ -2103,7 +2154,8 @@ describe('CdkDrag', () => {
         currentIndex: 3,
         item: groups[0][1],
         container: dropInstances[1],
-        previousContainer: dropInstances[0]
+        previousContainer: dropInstances[0],
+        isPointerOverContainer: true
       });
     }));
 
@@ -2133,7 +2185,8 @@ describe('CdkDrag', () => {
         currentIndex: 3,
         item: groups[0][1],
         container: dropInstances[1],
-        previousContainer: dropInstances[0]
+        previousContainer: dropInstances[0],
+        isPointerOverContainer: true
       });
     }));
 
@@ -2167,7 +2220,8 @@ describe('CdkDrag', () => {
         currentIndex: 0,
         item,
         container: fixture.componentInstance.dropInstances.toArray()[1],
-        previousContainer: fixture.componentInstance.dropInstances.first
+        previousContainer: fixture.componentInstance.dropInstances.first,
+        isPointerOverContainer: true
       });
 
       expect(dropContainers[0].contains(item.element.nativeElement)).toBe(true,
@@ -2656,7 +2710,7 @@ function dragElementViaMouse(fixture: ComponentFixture<any>,
   dispatchMouseEvent(document, 'mousemove', x, y);
   fixture.detectChanges();
 
-  dispatchMouseEvent(document, 'mouseup');
+  dispatchMouseEvent(document, 'mouseup', x, y);
   fixture.detectChanges();
 }
 
@@ -2695,7 +2749,7 @@ function dragElementViaTouch(fixture: ComponentFixture<any>,
   dispatchTouchEvent(document, 'touchmove', x, y);
   fixture.detectChanges();
 
-  dispatchTouchEvent(document, 'touchend');
+  dispatchTouchEvent(document, 'touchend', x, y);
   fixture.detectChanges();
 }
 

src/cdk/drag-drop/drag.ts

@@ -515,7 +515,7 @@ export class CdkDrag<T = any> implements AfterViewInit, OnDestroy {
   }
 
   /** Handler that is invoked when the user lifts their pointer up, after initiating a drag. */
-  private _pointerUp = () => {
+  private _pointerUp = (event: MouseEvent | TouchEvent) => {
     if (!this._isDragging()) {
       return;
     }
@@ -539,13 +539,13 @@ export class CdkDrag<T = any> implements AfterViewInit, OnDestroy {
     }
 
     this._animatePreviewToPlaceholder().then(() => {
-      this._cleanupDragArtifacts();
+      this._cleanupDragArtifacts(event);
       this._dragDropRegistry.stopDragging(this);
     });
   }
 
   /** Cleans up the DOM artifacts that were added to facilitate the element being dragged. */
-  private _cleanupDragArtifacts() {
+  private _cleanupDragArtifacts(event: MouseEvent | TouchEvent) {
     // Restore the element's visibility and insert it at its old position in the DOM.
     // It's important that we maintain the position, because moving the element around in the DOM
     // can throw off `NgFor` which does smart diffing and re-creates elements only when necessary,
@@ -564,16 +564,19 @@ export class CdkDrag<T = any> implements AfterViewInit, OnDestroy {
     // Re-enter the NgZone since we bound `document` events on the outside.
     this._ngZone.run(() => {
       const currentIndex = this.dropContainer.getItemIndex(this);
+      const {x, y} = this._getPointerPositionOnPage(event);
+      const isPointerOverContainer = this.dropContainer._isOverContainer(x, y);
 
       this.ended.emit({source: this});
       this.dropped.emit({
         item: this,
         currentIndex,
         previousIndex: this._initialContainer.getItemIndex(this),
         container: this.dropContainer,
-        previousContainer: this._initialContainer
+        previousContainer: this._initialContainer,
+        isPointerOverContainer
       });
-      this.dropContainer.drop(this, currentIndex, this._initialContainer);
+      this.dropContainer.drop(this, currentIndex, this._initialContainer, isPointerOverContainer);
       this.dropContainer = this._initialContainer;
     });
   }
@@ -587,11 +590,11 @@ export class CdkDrag<T = any> implements AfterViewInit, OnDestroy {
     let newContainer = this.dropContainer._getSiblingContainerFromPosition(this, x, y);
 
     // If we couldn't find a new container to move the item into, and the item has left it's
-    // initial container, check whether the it's allowed to return into its original container.
-    // This handles the case where two containers are connected one way and the user tries to
-    // undo dragging an item into a new container.
+    // initial container, check whether the it's over the initial container. This handles the
+    // case where two containers are connected one way and the user tries to undo dragging an
+    // item into a new container.
     if (!newContainer && this.dropContainer !== this._initialContainer &&
-        this._initialContainer._canReturnItem(x, y)) {
+        this._initialContainer._isOverContainer(x, y)) {
       newContainer = this._initialContainer;
     }
 

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

@@ -37,8 +37,11 @@ export interface CdkDropListContainer<T = any> {
    * @param item Item being dropped into the container.
    * @param currentIndex Index at which the item should be inserted.
    * @param previousContainer Container from which the item got dragged in.
+   * @param isPointerOverContainer Whether the user's pointer was over the
+   *    container when the item was dropped.
    */
-  drop(item: CdkDrag, currentIndex: number, previousContainer?: CdkDropListContainer): void;
+  drop(item: CdkDrag, currentIndex: number, previousContainer: CdkDropListContainer,
+        isPointerOverContainer: boolean): void;
 
   /**
    * Emits an event to indicate that the user moved an item into the container.
@@ -63,7 +66,7 @@ export interface CdkDropListContainer<T = any> {
   _draggables: QueryList<CdkDrag>;
   _getSiblingContainerFromPosition(item: CdkDrag, x: number, y: number):
       CdkDropListContainer | null;
-  _canReturnItem(x: number, y: number): boolean;
+  _isOverContainer(x: number, y: number): boolean;
 }
 
 /**

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

@@ -210,16 +210,19 @@ export class CdkDropList<T = any> implements OnInit, OnDestroy {
    * @param item Item being dropped into the container.
    * @param currentIndex Index at which the item should be inserted.
    * @param previousContainer Container from which the item got dragged in.
+   * @param isPointerOverContainer Whether the user's pointer was over the
+   *    container when the item was dropped.
    */
-  drop(item: CdkDrag, currentIndex: number, previousContainer: CdkDropList): void {
+  drop(item: CdkDrag, currentIndex: number, previousContainer: CdkDropList,
+    isPointerOverContainer: boolean): void {
     this._reset();
     this.dropped.emit({
       item,
       currentIndex,
       previousIndex: previousContainer.getItemIndex(item),
       container: this,
-      // TODO(crisbeto): reconsider whether to make this null if the containers are the same.
-      previousContainer
+      previousContainer,
+      isPointerOverContainer
     });
   }
 
@@ -386,12 +389,11 @@ export class CdkDropList<T = any> implements OnInit, OnDestroy {
   }
 
   /**
-   * Checks whether an item that started in this container can be returned to it,
-   * after it was moved out into another container.
-   * @param x Position of the item along the X axis.
-   * @param y Position of the item along the Y axis.
+   * Checks whether the user's pointer is positioned over the container.
+   * @param x Pointer position along the X axis.
+   * @param y Pointer position along the Y axis.
    */
-  _canReturnItem(x: number, y: number): boolean {
+  _isOverContainer(x: number, y: number): boolean {
     return isInsideClientRect(this._positionCache.self, x, y);
   }
 

tools/public_api_guard/cdk/drag-drop.d.ts

@@ -41,6 +41,7 @@ export interface CdkDragConfig {
 export interface CdkDragDrop<T, O = T> {
     container: CdkDropListContainer<T>;
     currentIndex: number;
+    isPointerOverContainer: boolean;
     item: CdkDrag;
     previousContainer: CdkDropListContainer<O>;
     previousIndex: number;
@@ -119,13 +120,13 @@ export declare class CdkDropList<T = any> implements OnInit, OnDestroy {
     orientation: 'horizontal' | 'vertical';
     sorted: EventEmitter<CdkDragSortEvent<T>>;
     constructor(element: ElementRef<HTMLElement>, _dragDropRegistry: DragDropRegistry<CdkDrag, CdkDropList<T>>, _changeDetectorRef: ChangeDetectorRef, _dir?: Directionality | undefined, _group?: CdkDropListGroup<CdkDropList<any>> | undefined);
-    _canReturnItem(x: number, y: number): boolean;
     _getSiblingContainerFromPosition(item: CdkDrag, x: number, y: number): CdkDropList | null;
+    _isOverContainer(x: number, y: number): boolean;
     _sortItem(item: CdkDrag, pointerX: number, pointerY: number, pointerDelta: {
         x: number;
         y: number;
     }): void;
-    drop(item: CdkDrag, currentIndex: number, previousContainer: CdkDropList): void;
+    drop(item: CdkDrag, currentIndex: number, previousContainer: CdkDropList, isPointerOverContainer: boolean): void;
     enter(item: CdkDrag, pointerX: number, pointerY: number): void;
     exit(item: CdkDrag): void;
     getItemIndex(item: CdkDrag): number;
@@ -142,13 +143,13 @@ export interface CdkDropListContainer<T = any> {
     id: string;
     lockAxis: 'x' | 'y';
     orientation: 'horizontal' | 'vertical';
-    _canReturnItem(x: number, y: number): boolean;
     _getSiblingContainerFromPosition(item: CdkDrag, x: number, y: number): CdkDropListContainer | null;
+    _isOverContainer(x: number, y: number): boolean;
     _sortItem(item: CdkDrag, pointerX: number, pointerY: number, delta: {
         x: number;
         y: number;
     }): void;
-    drop(item: CdkDrag, currentIndex: number, previousContainer?: CdkDropListContainer): void;
+    drop(item: CdkDrag, currentIndex: number, previousContainer: CdkDropListContainer, isPointerOverContainer: boolean): void;
     enter(item: CdkDrag, pointerX: number, pointerY: number): void;
     exit(item: CdkDrag): void;
     getItemIndex(item: CdkDrag): number;