feat(drag-drop): allow element to be passed in as the boundary

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

@@ -694,7 +694,18 @@ describe('CdkDrag', () => {
 
     it('should allow for dragging to be constrained to an element', fakeAsync(() => {
       const fixture = createComponent(StandaloneDraggable);
-      fixture.componentInstance.boundarySelector = '.wrapper';
+      fixture.componentInstance.boundary = '.wrapper';
+      fixture.detectChanges();
+      const dragElement = fixture.componentInstance.dragElement.nativeElement;
+
+      expect(dragElement.style.transform).toBeFalsy();
+      dragElementViaMouse(fixture, dragElement, 300, 300);
+      expect(dragElement.style.transform).toBe('translate3d(100px, 100px, 0px)');
+    }));
+
+    it('should be able to pass in a DOM node as the boundary', fakeAsync(() => {
+      const fixture = createComponent(StandaloneDraggable);
+      fixture.componentInstance.boundary = fixture.nativeElement.querySelector('.wrapper');
       fixture.detectChanges();
       const dragElement = fixture.componentInstance.dragElement.nativeElement;
 
@@ -3225,7 +3236,7 @@ describe('CdkDrag', () => {
     <div class="wrapper" style="width: 200px; height: 200px; background: green;">
       <div
         cdkDrag
-        [cdkDragBoundary]="boundarySelector"
+        [cdkDragBoundary]="boundary"
         [cdkDragStartDelay]="dragStartDelay"
         [cdkDragConstrainPosition]="constrainPosition"
         [cdkDragFreeDragPosition]="freeDragPosition"
@@ -3243,7 +3254,7 @@ class StandaloneDraggable {
   startedSpy = jasmine.createSpy('started spy');
   endedSpy = jasmine.createSpy('ended spy');
   releasedSpy = jasmine.createSpy('released spy');
-  boundarySelector: string;
+  boundary: string | HTMLElement;
   dragStartDelay: number | string;
   constrainPosition: (point: Point) => Point;
   freeDragPosition?: {x: number, y: number};

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

@@ -28,8 +28,9 @@ import {
   OnChanges,
   SimpleChanges,
   ChangeDetectorRef,
+  isDevMode,
 } from '@angular/core';
-import {coerceBooleanProperty, coerceNumberProperty} from '@angular/cdk/coercion';
+import {coerceBooleanProperty, coerceNumberProperty, coerceElement} from '@angular/cdk/coercion';
 import {Observable, Observer, Subject, merge} from 'rxjs';
 import {startWith, take, map, takeUntil, switchMap, tap} from 'rxjs/operators';
 import {
@@ -100,12 +101,27 @@ export class CdkDrag<T = any> implements AfterViewInit, OnChanges, OnDestroy {
    */
   @Input('cdkDragRootElement') rootElementSelector: string;
 
+  /**
+   * Node or selector that will be used to determine the element to which the draggable's
+   * position will be constrained. If a string is passed in, it'll be used as a selector that
+   * will be matched starting from the element's parent and going up the DOM until a match
+   * has been found.
+   */
+  @Input('cdkDragBoundary') boundaryElement: string | ElementRef<HTMLElement> | HTMLElement;
+
   /**
    * Selector that will be used to determine the element to which the draggable's position will
    * be constrained. Matching starts from the element's parent and goes up the DOM until a matching
-   * element has been found.
+   * element has been found
+   * @deprecated Use `boundaryElement` instead.
+   * @breaking-change 9.0.0
    */
-  @Input('cdkDragBoundary') boundaryElementSelector: string;
+  get boundaryElementSelector(): string {
+    return typeof this.boundaryElement === 'string' ? this.boundaryElement : undefined!;
+  }
+  set boundaryElementSelector(selector: string) {
+    this.boundaryElement = selector;
+  }
 
   /**
    * Amount of milliseconds to wait after the user has put their
@@ -292,10 +308,25 @@ export class CdkDrag<T = any> implements AfterViewInit, OnChanges, OnDestroy {
     this._dragRef.withRootElement(rootElement || element);
   }
 
-  /** Gets the boundary element, based on the `boundaryElementSelector`. */
+  /** Gets the boundary element, based on the `boundaryElement` value. */
   private _getBoundaryElement() {
-    const selector = this.boundaryElementSelector;
-    return selector ? getClosestMatchingAncestor(this.element.nativeElement, selector) : null;
+    const boundary = this.boundaryElement;
+
+    if (!boundary) {
+      return null;
+    }
+
+    if (typeof boundary === 'string') {
+      return getClosestMatchingAncestor(this.element.nativeElement, boundary);
+    }
+
+    const element = coerceElement(boundary);
+
+    if (isDevMode() && !element.contains(this.element.nativeElement)) {
+      throw Error('Draggable element is not inside of the node passed into cdkDragBoundary.');
+    }
+
+    return element;
   }
 
   /** Syncs the inputs of the CdkDrag with the options of the underlying DragRef. */

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

@@ -11,6 +11,7 @@ export declare class CdkDrag<T = any> implements AfterViewInit, OnChanges, OnDes
     _handles: QueryList<CdkDragHandle>;
     _placeholderTemplate: CdkDragPlaceholder;
     _previewTemplate: CdkDragPreview;
+    boundaryElement: string | ElementRef<HTMLElement> | HTMLElement;
     boundaryElementSelector: string;
     constrainPosition?: (point: Point) => Point;
     data: T;