feat(drag-drop): add the ability to set an alternate root element (#12895)

Adds the `cdkDragRootElement` input which allows consumers to pass in a selector that will be used to determine which elements is going to become draggable, starting from the `cdkDrag` element and going up the DOM.

Author: crisbeto

src/cdk/drag-drop/drag-drop.md

@@ -116,3 +116,12 @@ specific axis, you can set `cdkDragLockAxis` on `cdkDrag` or `lockAxis` on `<cdk
 to either `"x"` or `"y"`.
 
 <!-- example(cdk-drag-drop-axis-lock) -->
+
+### Alternate drag root element
+If there's an element that you want to make draggable, but you don't have direct access to it, you
+can use the `cdkDragRootElement` attribute. The attribute works by accepting a selector and looking
+up the DOM until it finds an element that matches the selector. If an element is found, it'll become
+the element that is moved as the user is dragging. This is useful for cases like making a dialog
+draggable.
+
+<!-- example(cdk-drag-drop-root-element) -->

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

@@ -322,6 +322,22 @@ describe('CdkDrag', () => {
       expect(element.classList).not.toContain('cdk-drag-dragging');
     }));
 
+    it('should be able to set an alternate drag root element', fakeAsync(() => {
+      const fixture = createComponent(DraggableWithAlternateRoot);
+      fixture.detectChanges();
+
+      const dragRoot = fixture.componentInstance.dragRoot.nativeElement;
+      const dragElement = fixture.componentInstance.dragElement.nativeElement;
+
+      expect(dragRoot.style.transform).toBeFalsy();
+      expect(dragElement.style.transform).toBeFalsy();
+
+      dragElementViaMouse(fixture, dragRoot, 50, 100);
+
+      expect(dragRoot.style.transform).toBe('translate3d(50px, 100px, 0px)');
+      expect(dragElement.style.transform).toBeFalsy();
+    }));
+
   });
 
   describe('draggable with a handle', () => {
@@ -1597,6 +1613,23 @@ class ConnectedDropZones implements AfterViewInit {
 }
 
 
+@Component({
+  template: `
+    <div #dragRoot class="alternate-root" style="width: 200px; height: 200px; background: hotpink">
+      <div
+        cdkDrag
+        cdkDragRootElement=".alternate-root"
+        #dragElement
+        style="width: 100px; height: 100px; background: red;"></div>
+    </div>
+  `
+})
+class DraggableWithAlternateRoot {
+  @ViewChild('dragElement') dragElement: ElementRef<HTMLElement>;
+  @ViewChild('dragRoot') dragRoot: ElementRef<HTMLElement>;
+  @ViewChild(CdkDrag) dragInstance: CdkDrag;
+}
+
 
 /**
  * Drags an element to a position on the page using the mouse.

src/cdk/drag-drop/drag.ts

@@ -10,6 +10,7 @@ import {Directionality} from '@angular/cdk/bidi';
 import {ViewportRuler} from '@angular/cdk/scrolling';
 import {DOCUMENT} from '@angular/common';
 import {
+  AfterViewInit,
   ContentChild,
   ContentChildren,
   Directive,
@@ -27,7 +28,7 @@ import {
   ViewContainerRef,
 } from '@angular/core';
 import {merge, Observable, Subject} from 'rxjs';
-import {takeUntil} from 'rxjs/operators';
+import {takeUntil, take} from 'rxjs/operators';
 import {DragDropRegistry} from './drag-drop-registry';
 import {
   CdkDragDrop,
@@ -60,11 +61,9 @@ const POINTER_DIRECTION_CHANGE_THRESHOLD = 5;
   host: {
     'class': 'cdk-drag',
     '[class.cdk-drag-dragging]': '_isDragging()',
-    '(mousedown)': '_startDragging($event)',
-    '(touchstart)': '_startDragging($event)',
   }
 })
-export class CdkDrag<T = any> implements OnDestroy {
+export class CdkDrag<T = any> implements AfterViewInit, OnDestroy {
   private _document: Document;
   private _destroyed = new Subject<void>();
 
@@ -127,6 +126,9 @@ export class CdkDrag<T = any> implements OnDestroy {
   /** Pointer position at which the last change in the delta occurred. */
   private _pointerPositionAtLastDirectionChange: Point;
 
+  /** Root element that will be dragged by the user. */
+  private _rootElement: HTMLElement;
+
   /** Elements that can be used to drag the draggable item. */
   @ContentChildren(CdkDragHandle) _handles: QueryList<CdkDragHandle>;
 
@@ -142,6 +144,13 @@ export class CdkDrag<T = any> implements OnDestroy {
   /** Locks the position of the dragged element along the specified axis. */
   @Input('cdkDragLockAxis') lockAxis: 'x' | 'y';
 
+  /**
+   * Selector that will be used to determine the root draggable element, starting from
+   * the `cdkDrag` element and going up the DOM. Passing an alternate root element is useful
+   * when trying to enable dragging on an element that you might not have access to.
+   */
+  @Input('cdkDragRootElement') rootElementSelector: string;
+
   /** Emits when the user starts dragging the item. */
   @Output('cdkDragStarted') started: EventEmitter<CdkDragStart> = new EventEmitter<CdkDragStart>();
 
@@ -197,7 +206,26 @@ export class CdkDrag<T = any> implements OnDestroy {
     return this._placeholder;
   }
 
+  /** Returns the root draggable element. */
+  getRootElement(): HTMLElement {
+    return this._rootElement;
+  }
+
+  ngAfterViewInit() {
+    // We need to wait for the zone to stabilize, in order for the reference
+    // element to be in the proper place in the DOM. This is mostly relevant
+    // for draggable elements inside portals since they get stamped out in
+    // their original DOM position and then they get transferred to the portal.
+    this._ngZone.onStable.asObservable().pipe(take(1)).subscribe(() => {
+      const rootElement = this._rootElement = this._getRootElement();
+      rootElement.addEventListener('mousedown', this._startDragging);
+      rootElement.addEventListener('touchstart', this._startDragging);
+    });
+  }
+
   ngOnDestroy() {
+    this._rootElement.removeEventListener('mousedown', this._startDragging);
+    this._rootElement.removeEventListener('touchstart', this._startDragging);
     this._destroyPreview();
     this._destroyPlaceholder();
 
@@ -206,7 +234,7 @@ export class CdkDrag<T = any> implements OnDestroy {
     if (this._isDragging()) {
       // Since we move out the element to the end of the body while it's being
       // dragged, we have to make sure that it's removed if it gets destroyed.
-      this._removeElement(this.element.nativeElement);
+      this._removeElement(this._rootElement);
     }
 
     this._nextSibling = null;
@@ -217,7 +245,7 @@ export class CdkDrag<T = any> implements OnDestroy {
   }
 
   /** Starts the dragging sequence. */
-  _startDragging(event: MouseEvent | TouchEvent) {
+  _startDragging = (event: MouseEvent | TouchEvent) => {
     // Delegate the event based on whether it started from a handle or the element itself.
     if (this._handles.length) {
       const targetHandle = this._handles.find(handle => {
@@ -227,10 +255,10 @@ export class CdkDrag<T = any> implements OnDestroy {
       });
 
       if (targetHandle) {
-        this._pointerDown(targetHandle.element, event);
+        this._pointerDown(targetHandle.element.nativeElement, event);
       }
     } else {
-      this._pointerDown(this.element, event);
+      this._pointerDown(this._rootElement, event);
     }
   }
 
@@ -240,7 +268,7 @@ export class CdkDrag<T = any> implements OnDestroy {
   }
 
   /** Handler for when the pointer is pressed down on the element or the handle. */
-  private _pointerDown = (referenceElement: ElementRef<HTMLElement>,
+  private _pointerDown = (referenceElement: HTMLElement,
                           event: MouseEvent | TouchEvent) => {
 
     const isDragging = this._isDragging();
@@ -277,7 +305,7 @@ export class CdkDrag<T = any> implements OnDestroy {
     this.started.emit({source: this});
 
     if (this.dropContainer) {
-      const element = this.element.nativeElement;
+      const element = this._rootElement;
 
       // Grab the `nextSibling` before the preview and placeholder
       // have been created so we don't get the preview by accident.
@@ -318,7 +346,7 @@ export class CdkDrag<T = any> implements OnDestroy {
           pointerPosition.x - this._pickupPositionOnPage.x + this._passiveTransform.x;
       activeTransform.y =
           pointerPosition.y - this._pickupPositionOnPage.y + this._passiveTransform.y;
-      this._setTransform(this.element.nativeElement, activeTransform.x, activeTransform.y);
+      this._setTransform(this._rootElement, activeTransform.x, activeTransform.y);
     }
 
     // Since this event gets fired for every pixel while dragging, we only
@@ -362,12 +390,12 @@ export class CdkDrag<T = any> implements OnDestroy {
     // 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,
     // while moving the existing elements in all other cases.
-    this.element.nativeElement.style.display = '';
+    this._rootElement.style.display = '';
 
     if (this._nextSibling) {
-      this._nextSibling.parentNode!.insertBefore(this.element.nativeElement, this._nextSibling);
+      this._nextSibling.parentNode!.insertBefore(this._rootElement, this._nextSibling);
     } else {
-      this._placeholder.parentNode!.appendChild(this.element.nativeElement);
+      this._placeholder.parentNode!.appendChild(this._rootElement);
     }
 
     this._destroyPreview();
@@ -430,7 +458,7 @@ export class CdkDrag<T = any> implements OnDestroy {
       this._previewRef = viewRef;
       this._setTransform(preview, this._pickupPositionOnPage.x, this._pickupPositionOnPage.y);
     } else {
-      const element = this.element.nativeElement;
+      const element = this._rootElement;
       const elementRect = element.getBoundingClientRect();
 
       preview = element.cloneNode(true) as HTMLElement;
@@ -456,7 +484,7 @@ export class CdkDrag<T = any> implements OnDestroy {
       );
       placeholder = this._placeholderRef.rootNodes[0];
     } else {
-      placeholder = this.element.nativeElement.cloneNode(true) as HTMLElement;
+      placeholder = this._rootElement.cloneNode(true) as HTMLElement;
     }
 
     placeholder.classList.add('cdk-drag-placeholder');
@@ -468,10 +496,10 @@ export class CdkDrag<T = any> implements OnDestroy {
    * @param referenceElement Element that initiated the dragging.
    * @param event Event that initiated the dragging.
    */
-  private _getPointerPositionInElement(referenceElement: ElementRef<HTMLElement>,
+  private _getPointerPositionInElement(referenceElement: HTMLElement,
                                        event: MouseEvent | TouchEvent): Point {
-    const elementRect = this.element.nativeElement.getBoundingClientRect();
-    const handleElement = referenceElement === this.element ? null : referenceElement.nativeElement;
+    const elementRect = this._rootElement.getBoundingClientRect();
+    const handleElement = referenceElement === this._rootElement ? null : referenceElement;
     const referenceRect = handleElement ? handleElement.getBoundingClientRect() : elementRect;
     const x = this._isTouchEvent(event) ?
         event.targetTouches[0].pageX - referenceRect.left - this._scrollPosition.left :
@@ -632,6 +660,23 @@ export class CdkDrag<T = any> implements OnDestroy {
       positionSinceLastChange.y = y;
     }
   }
+
+  /** Gets the root draggable element, based on the `rootElementSelector`. */
+  private _getRootElement(): HTMLElement {
+    if (this.rootElementSelector) {
+      let currentElement = this.element.nativeElement.parentElement as HTMLElement | null;
+
+      while (currentElement) {
+        if (currentElement.matches(this.rootElementSelector)) {
+          return currentElement;
+        }
+
+        currentElement = currentElement.parentElement;
+      }
+    }
+
+    return this.element.nativeElement;
+  }
 }
 
 /** Parses a CSS time value to milliseconds. */
@@ -650,7 +695,6 @@ function getTransitionDurationInMs(element: HTMLElement): number {
   return parseCssTimeUnitsToMs(rawDuration) + parseCssTimeUnitsToMs(rawDelay);
 }
 
-
 /** Point on the page or within an element. */
 interface Point {
   x: number;

src/cdk/drag-drop/drop.ts

@@ -187,7 +187,7 @@ export class CdkDrop<T = any> implements OnInit, OnDestroy {
     // Don't use items that are being dragged as a reference, because
     // their element has been moved down to the bottom of the body.
     if (newPositionReference && !this._dragDropRegistry.isDragging(newPositionReference)) {
-      const element = newPositionReference.element.nativeElement;
+      const element = newPositionReference.getRootElement();
       element.parentElement!.insertBefore(placeholder, element);
       this._activeDraggables.splice(newIndex, 0, item);
     } else {
@@ -277,7 +277,7 @@ export class CdkDrop<T = any> implements OnInit, OnDestroy {
       const isDraggedItem = sibling.drag === item;
       const offset = isDraggedItem ? itemOffset : siblingOffset;
       const elementToOffset = isDraggedItem ? item.getPlaceholderElement() :
-                                              sibling.drag.element.nativeElement;
+                                              sibling.drag.getRootElement();
 
       // Update the offset to reflect the new position.
       sibling.offset += offset;
@@ -320,7 +320,7 @@ export class CdkDrop<T = any> implements OnInit, OnDestroy {
             // If the element is being dragged, we have to measure the
             // placeholder, because the element is hidden.
             drag.getPlaceholderElement() :
-            drag.element.nativeElement;
+            drag.getRootElement();
         const clientRect = elementToMeasure.getBoundingClientRect();
 
         return {
@@ -355,7 +355,7 @@ export class CdkDrop<T = any> implements OnInit, OnDestroy {
     this._dragging = false;
 
     // TODO(crisbeto): may have to wait for the animations to finish.
-    this._activeDraggables.forEach(item => item.element.nativeElement.style.transform = '');
+    this._activeDraggables.forEach(item => item.getRootElement().style.transform = '');
     this._activeDraggables = [];
     this._positionCache.items = [];
     this._positionCache.siblings = [];

src/demo-app/dialog/dialog-demo.ts

@@ -90,16 +90,19 @@ export class DialogDemo {
 @Component({
   selector: 'demo-jazz-dialog',
   template: `
-  <p>It's Jazz!</p>
-
-  <mat-form-field>
-    <mat-label>How much?</mat-label>
-    <input matInput #howMuch>
-  </mat-form-field>
-
-  <p> {{ data.message }} </p>
-  <button type="button" (click)="dialogRef.close(howMuch.value)">Close dialog</button>
-  <button (click)="togglePosition()">Change dimensions</button>`
+    <div cdkDrag cdkDragRootElement=".cdk-overlay-pane">
+      <p>It's Jazz!</p>
+
+      <mat-form-field>
+        <mat-label>How much?</mat-label>
+        <input matInput #howMuch>
+      </mat-form-field>
+
+      <p cdkDragHandle> {{ data.message }} </p>
+      <button type="button" (click)="dialogRef.close(howMuch.value)">Close dialog</button>
+      <button (click)="togglePosition()">Change dimensions</button>
+    </div>
+  `
 })
 export class JazzDialog {
   private _dimesionToggle = false;

src/material-examples/cdk-drag-drop-root-element/cdk-drag-drop-root-element-example.css

@@ -0,0 +1,21 @@
+.dialog-content {
+  width: 200px;
+  height: 200px;
+  border: solid 1px #ccc;
+  cursor: move;
+  display: flex;
+  justify-content: center;
+  align-items: center;
+  background: #fff;
+  border-radius: 4px;
+  transition: box-shadow 200ms cubic-bezier(0, 0, 0.2, 1);
+  box-shadow: 0 3px 1px -2px rgba(0, 0, 0, 0.2),
+              0 2px 2px 0 rgba(0, 0, 0, 0.14),
+              0 1px 5px 0 rgba(0, 0, 0, 0.12);
+}
+
+.dialog-content:active {
+  box-shadow: 0 5px 5px -3px rgba(0, 0, 0, 0.2),
+              0 8px 10px 1px rgba(0, 0, 0, 0.14),
+              0 3px 14px 2px rgba(0, 0, 0, 0.12);
+}

src/material-examples/cdk-drag-drop-root-element/cdk-drag-drop-root-element-example.html

@@ -0,0 +1,7 @@
+<button (click)="openDialog()">Open a draggable dialog</button>
+
+<ng-template>
+  <div class="dialog-content" cdkDrag cdkDragRootElement=".cdk-overlay-pane">
+    Drag the dialog around!
+  </div>
+</ng-template>