feat(drag-drop): add support for sorting animations

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

@@ -562,7 +562,7 @@ describe('CdkDrag', () => {
         // Add a few pixels to the left offset so we get some overlap.
         dispatchMouseEvent(document, 'mousemove', elementRect.left + 5, elementRect.top);
         fixture.detectChanges();
-        expect(getElementIndex(placeholder)).toBe(i);
+        expect(getElementIndexByPosition(placeholder, 'left')).toBe(i);
       }
 
       dispatchMouseEvent(document, 'mouseup');
@@ -590,7 +590,7 @@ describe('CdkDrag', () => {
         // Remove a few pixels from the right offset so we get some overlap.
         dispatchMouseEvent(document, 'mousemove', elementRect.right - 5, elementRect.top);
         fixture.detectChanges();
-        expect(getElementIndex(placeholder)).toBe(Math.min(i + 1, items.length - 1));
+        expect(getElementIndexByPosition(placeholder, 'left')).toBe(i);
       }
 
       dispatchMouseEvent(document, 'mouseup');
@@ -660,6 +660,31 @@ describe('CdkDrag', () => {
       expect(placeholder.textContent!.trim()).toContain('Custom placeholder');
     }));
 
+    it('should clear the `transform` value from siblings when item is dropped`', fakeAsync(() => {
+      const fixture = createComponent(DraggableInDropZone);
+      fixture.detectChanges();
+
+      const dragItems = fixture.componentInstance.dragItems;
+      const firstItem = dragItems.first;
+      const thirdItem = dragItems.toArray()[2].element.nativeElement;
+      const thirdItemRect = thirdItem.getBoundingClientRect();
+
+      dispatchMouseEvent(firstItem.element.nativeElement, 'mousedown');
+      fixture.detectChanges();
+
+      dispatchMouseEvent(document, 'mousemove', thirdItemRect.left + 1, thirdItemRect.top + 1);
+      fixture.detectChanges();
+
+      expect(thirdItem.style.transform).toBeTruthy();
+
+      dispatchMouseEvent(document, 'mouseup');
+      fixture.detectChanges();
+      flush();
+      fixture.detectChanges();
+
+      expect(thirdItem.style.transform).toBeFalsy();
+    }));
+
   });
 
   describe('in a connected drop container', () => {
@@ -1151,9 +1176,15 @@ function dragElementViaTouch(fixture: ComponentFixture<any>,
   fixture.detectChanges();
 }
 
-/** Gets the index of a DOM element inside its parent. */
-function getElementIndex(element: HTMLElement) {
-  return element.parentElement ? Array.from(element.parentElement.children).indexOf(element) : -1;
+/** Gets the index of an element among its siblings, based on their position on the page. */
+function getElementIndexByPosition(element: HTMLElement, direction: 'top' | 'left') {
+  if (!element.parentElement) {
+    return -1;
+  }
+
+  return Array.from(element.parentElement.children)
+      .sort((a, b) => a.getBoundingClientRect()[direction] - b.getBoundingClientRect()[direction])
+      .indexOf(element);
 }
 
 /**
@@ -1193,7 +1224,7 @@ function assertDownwardSorting(fixture: ComponentFixture<any>, items: Element[])
     // Add a few pixels to the top offset so we get some overlap.
     dispatchMouseEvent(document, 'mousemove', elementRect.left, elementRect.top + 5);
     fixture.detectChanges();
-    expect(getElementIndex(placeholder)).toBe(i);
+    expect(getElementIndexByPosition(placeholder, 'top')).toBe(i);
   }
 
   dispatchMouseEvent(document, 'mouseup');
@@ -1222,7 +1253,7 @@ function assertUpwardSorting(fixture: ComponentFixture<any>, items: Element[]) {
     // Remove a few pixels from the bottom offset so we get some overlap.
     dispatchMouseEvent(document, 'mousemove', elementRect.left, elementRect.bottom - 5);
     fixture.detectChanges();
-    expect(getElementIndex(placeholder)).toBe(Math.min(i + 1, items.length - 1));
+    expect(getElementIndexByPosition(placeholder, 'top')).toBe(i);
   }
 
   dispatchMouseEvent(document, 'mouseup');

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

@@ -35,8 +35,8 @@ import {CdkDragDropRegistry} from './drag-drop-registry';
 import {Subject, merge} from 'rxjs';
 import {takeUntil} from 'rxjs/operators';
 
-// TODO: add auto-scrolling functionality.
-// TODO: add an API for moving a draggable up/down the
+// TODO(crisbeto): add auto-scrolling functionality.
+// TODO(crisbeto): add an API for moving a draggable up/down the
 // list programmatically. Useful for keyboard controls.
 
 /** Element that can be moved inside a CdkDrop container. */
@@ -236,7 +236,7 @@ export class CdkDrag<T = any> implements OnDestroy {
 
   /** Handler that is invoked when the user moves their pointer after they've initiated a drag. */
   private _pointerMove = (event: MouseEvent | TouchEvent) => {
-    // TODO: this should start dragging after a certain threshold,
+    // TODO(crisbeto): this should start dragging after a certain threshold,
     // otherwise we risk interfering with clicks on the element.
     if (!this._dragDropRegistry.isDragging(this)) {
       return;
@@ -279,8 +279,6 @@ export class CdkDrag<T = any> implements OnDestroy {
 
   /** Cleans up the DOM artifacts that were added to facilitate the element being dragged. */
   private _cleanupDragArtifacts() {
-    const currentIndex = this._getElementIndexInDom(this._placeholder);
-
     // 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,
@@ -298,6 +296,8 @@ export class CdkDrag<T = any> implements OnDestroy {
 
     // Re-enter the NgZone since we bound `document` events on the outside.
     this._ngZone.run(() => {
+      const currentIndex = this.dropContainer.getItemIndex(this);
+
       this.ended.emit({source: this});
       this.dropped.emit({
         item: this,
@@ -328,7 +328,7 @@ export class CdkDrag<T = any> implements OnDestroy {
         // Notify the new container that the item has entered.
         this.entered.emit({ item: this, container: newContainer });
         this.dropContainer = newContainer;
-        this.dropContainer.enter(this);
+        this.dropContainer.enter(this, x, y);
       });
     }
 
@@ -386,37 +386,6 @@ export class CdkDrag<T = any> implements OnDestroy {
     return placeholder;
   }
 
-  /** Gets the index of an element, based on its index in the DOM. */
-  private _getElementIndexInDom(element: HTMLElement): number {
-    // Note: we may be able to figure this in memory while sorting, but doing so won't be very
-    // reliable when transferring between containers, because the new container doesn't have
-    // the proper indices yet. Also this will work better for the case where the consumer
-    // isn't using an `ngFor` to render the list.
-    if (!element.parentElement) {
-      return -1;
-    }
-
-    // Avoid accessing `children` and `children.length` too much since they're a "live collection".
-    let index = 0;
-    const siblings = element.parentElement.children;
-    const siblingsLength = siblings.length;
-    const draggableElements = this.dropContainer._draggables
-        .filter(item => item !== this)
-        .map(item => item.element.nativeElement);
-
-    // Loop through the sibling elements to find out the index of the
-    // current one, while skipping any elements that aren't draggable.
-    for (let i = 0; i < siblingsLength; i++) {
-      if (siblings[i] === element) {
-        return index;
-      } else if (draggableElements.indexOf(siblings[i] as HTMLElement) > -1) {
-        index++;
-      }
-    }
-
-    return -1;
-  }
-
   /**
    * Figures out the coordinates at which an element was picked up.
    * @param referenceElement Element that initiated the dragging.

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

@@ -30,8 +30,10 @@ export interface CdkDropContainer<T = any> {
   /**
    * Emits an event to indicate that the user moved an item into the container.
    * @param item Item that was moved into the container.
+   * @param xOffset Position of the item along the X axis.
+   * @param yOffset Position of the item along the Y axis.
    */
-  enter(item: CdkDrag): void;
+  enter(item: CdkDrag, xOffset: number, yOffset: number): void;
 
   /**
    * Removes an item from the container after it was dragged into another container by the user.