fix(drag-drop): not picking up handle that isn't a direct descendant

Fixes not being able to have a drag handle that isn't a direct descendant of `CdkDrag`.

Fixes #13335.

Author: crisbeto

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

@@ -6,7 +6,8 @@
  * found in the LICENSE file at https://angular.io/license
  */
 
-import {Directive, ElementRef} from '@angular/core';
+import {Directive, ElementRef, Inject, Optional} from '@angular/core';
+import {CDK_DRAG_PARENT} from './drag-parent';
 
 /** Handle that can be used to drag and CdkDrag instance. */
 @Directive({
@@ -16,5 +17,13 @@ import {Directive, ElementRef} from '@angular/core';
   }
 })
 export class CdkDragHandle {
-  constructor(public element: ElementRef<HTMLElement>) {}
+  /** Closest parent draggable instance. */
+  _parentDrag: {} | undefined;
+
+  constructor(
+    public element: ElementRef<HTMLElement>,
+    @Inject(CDK_DRAG_PARENT) @Optional() parentDrag?: any) {
+
+    this._parentDrag = parentDrag;
+  }
 }

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

@@ -0,0 +1,17 @@
+/**
+ * @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 {InjectionToken} from '@angular/core';
+
+/**
+ * Injection token that can be used for a `CdkDrag` to provide itself as a parent to the
+ * drag-specific child directive (`CdkDragHandle`, `CdkDragPreview` etc.). Used primarily
+ * to avoid circular imports.
+ * @docs-private
+ */
+export const CDK_DRAG_PARENT = new InjectionToken<{}>('CDK_DRAG_PARENT');

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

@@ -33,7 +33,7 @@ describe('CdkDrag', () => {
     ComponentFixture<T> {
     TestBed.configureTestingModule({
       imports: [DragDropModule],
-      declarations: [componentType],
+      declarations: [componentType, PassthroughComponent],
       providers,
     }).compileComponents();
 
@@ -392,6 +392,23 @@ describe('CdkDrag', () => {
       expect(dragElement.style.transform).toBe('translate3d(150px, 300px, 0px)');
     }));
 
+    it('should be able to drag with a handle that is not a direct descendant', fakeAsync(() => {
+      const fixture = createComponent(StandaloneDraggableWithIndirectHandle);
+      fixture.detectChanges();
+      const dragElement = fixture.componentInstance.dragElement.nativeElement;
+      const handle = fixture.componentInstance.handleElement.nativeElement;
+
+      expect(dragElement.style.transform).toBeFalsy();
+      dragElementViaMouse(fixture, dragElement, 50, 100);
+
+      expect(dragElement.style.transform)
+          .toBeFalsy('Expected not to be able to drag the element by itself.');
+
+      dragElementViaMouse(fixture, handle, 50, 100);
+      expect(dragElement.style.transform)
+          .toBe('translate3d(50px, 100px, 0px)', 'Expected to drag the element by its handle.');
+    }));
+
   });
 
   describe('in a drop container', () => {
@@ -1640,6 +1657,26 @@ class StandaloneDraggableWithDelayedHandle {
   showHandle = false;
 }
 
+@Component({
+  template: `
+    <div #dragElement cdkDrag
+      style="width: 100px; height: 100px; background: red; position: relative">
+
+      <passthrough-component>
+        <div
+          #handleElement
+          cdkDragHandle
+          style="width: 10px; height: 10px; background: green;"></div>
+      </passthrough-component>
+    </div>
+  `
+})
+class StandaloneDraggableWithIndirectHandle {
+  @ViewChild('dragElement') dragElement: ElementRef<HTMLElement>;
+  @ViewChild('handleElement') handleElement: ElementRef<HTMLElement>;
+}
+
+
 @Component({
   encapsulation: ViewEncapsulation.None,
   styles: [`
@@ -1868,6 +1905,16 @@ class ConnectedDropZonesWithSingleItems {
   droppedSpy = jasmine.createSpy('dropped spy');
 }
 
+/**
+ * Component that passes through whatever content is projected into it.
+ * Used to test having drag elements being projected into a component.
+ */
+@Component({
+  selector: 'passthrough-component',
+  template: '<ng-content></ng-content>'
+})
+class PassthroughComponent {}
+
 /**
  * Drags an element to a position on the page using the mouse.
  * @param fixture Fixture on which to run change detection.

src/cdk/drag-drop/drag.ts

@@ -42,6 +42,7 @@ import {CdkDragHandle} from './drag-handle';
 import {CdkDragPlaceholder} from './drag-placeholder';
 import {CdkDragPreview} from './drag-preview';
 import {CDK_DROP_CONTAINER, CdkDropContainer} from './drop-container';
+import {CDK_DRAG_PARENT} from './drag-parent';
 
 
 // TODO(crisbeto): add auto-scrolling functionality.
@@ -61,7 +62,11 @@ const POINTER_DIRECTION_CHANGE_THRESHOLD = 5;
   host: {
     'class': 'cdk-drag',
     '[class.cdk-drag-dragging]': '_isDragging()',
-  }
+  },
+  providers: [{
+    provide: CDK_DRAG_PARENT,
+    useExisting: CdkDrag
+  }]
 })
 export class CdkDrag<T = any> implements AfterViewInit, OnDestroy {
   private _document: Document;
@@ -130,7 +135,7 @@ export class CdkDrag<T = any> implements AfterViewInit, OnDestroy {
   private _rootElement: HTMLElement;
 
   /** Elements that can be used to drag the draggable item. */
-  @ContentChildren(CdkDragHandle) _handles: QueryList<CdkDragHandle>;
+  @ContentChildren(CdkDragHandle, {descendants: true}) _handles: QueryList<CdkDragHandle>;
 
   /** Element that will be used as a template to create the draggable item's preview. */
   @ContentChild(CdkDragPreview) _previewTemplate: CdkDragPreview;
@@ -250,9 +255,12 @@ export class CdkDrag<T = any> implements AfterViewInit, OnDestroy {
 
   /** Starts the dragging sequence. */
   _startDragging = (event: MouseEvent | TouchEvent) => {
+    // Skip handles inside descendant `CdkDrag` instances.
+    const handles = this._handles.filter(handle => handle._parentDrag === this);
+
     // 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 => {
+    if (handles.length) {
+      const targetHandle = handles.find(handle => {
         const element = handle.element.nativeElement;
         const target = event.target;
         return !!target && (target === element || element.contains(target as HTMLElement));