fix(expansion-panel): implement keyboard controls

Based on the [accessibility guidelines](https://www.w3.org/TR/wai-aria-practices-1.1/#accordion), accordions should be able to support moving focus using the keyboard. These changes implement the keyboard support and move some things around to avoid circular imports.

Author: crisbeto

src/lib/expansion/accordion-base.ts

@@ -0,0 +1,38 @@
+/**
+ * @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';
+import {CdkAccordion} from '@angular/cdk/accordion';
+
+/** MatAccordion's display modes. */
+export type MatAccordionDisplayMode = 'default' | 'flat';
+
+/**
+ * Base interface for a `MatAccordion`.
+ * @docs-private
+ */
+export interface MatAccordionBase extends CdkAccordion {
+  /** Whether the expansion indicator should be hidden. */
+  hideToggle: boolean;
+
+  /** Display mode used for all expansion panels in the accordion. */
+  displayMode: MatAccordionDisplayMode;
+
+  /** Handles keyboard events coming in from the panel headers. */
+  _handleHeaderKeydown: (event: KeyboardEvent) => void;
+
+  /** Handles focus events on the panel headers. */
+  _handleHeaderFocus: (header: any) => void;
+}
+
+
+/**
+ * Token used to provide a `MatAccordion` to `MatExpansionPanel`.
+ * Used primarily to avoid circular imports between `MatAccordion` and `MatExpansionPanel`.
+ */
+export const MAT_ACCORDION = new InjectionToken<MatAccordionBase>('MAT_ACCORDION');

src/lib/expansion/accordion.spec.ts

@@ -1,11 +1,21 @@
-import {async, TestBed} from '@angular/core/testing';
-import {Component, ViewChild} from '@angular/core';
+import {async, TestBed, inject} from '@angular/core/testing';
+import {Component, ViewChild, QueryList, ViewChildren} from '@angular/core';
 import {By} from '@angular/platform-browser';
 import {BrowserAnimationsModule} from '@angular/platform-browser/animations';
-import {MatExpansionModule, MatAccordion, MatExpansionPanel} from './index';
+import {
+  MatExpansionModule,
+  MatAccordion,
+  MatExpansionPanel,
+  MatExpansionPanelHeader,
+} from './index';
+import {dispatchKeyboardEvent} from '@angular/cdk/testing';
+import {DOWN_ARROW, UP_ARROW, HOME, END} from '@angular/cdk/keycodes';
+import {FocusMonitor} from '@angular/cdk/a11y';
 
 
 describe('MatAccordion', () => {
+  let focusMonitor: FocusMonitor;
+
   beforeEach(async(() => {
     TestBed.configureTestingModule({
       imports: [
@@ -18,41 +28,53 @@ describe('MatAccordion', () => {
       ],
     });
     TestBed.compileComponents();
+
+    inject([FocusMonitor], (fm: FocusMonitor) => {
+      focusMonitor = fm;
+    })();
   }));
 
   it('should ensure only one item is expanded at a time', () => {
     const fixture = TestBed.createComponent(SetOfItems);
+    fixture.detectChanges();
+
     const items = fixture.debugElement.queryAll(By.css('.mat-expansion-panel'));
+    const panelInstances = fixture.componentInstance.panels.toArray();
 
-    fixture.componentInstance.firstPanelExpanded = true;
+    panelInstances[0].expanded = true;
     fixture.detectChanges();
     expect(items[0].classes['mat-expanded']).toBeTruthy();
     expect(items[1].classes['mat-expanded']).toBeFalsy();
 
-    fixture.componentInstance.secondPanelExpanded = true;
+    panelInstances[1].expanded = true;
     fixture.detectChanges();
     expect(items[0].classes['mat-expanded']).toBeFalsy();
     expect(items[1].classes['mat-expanded']).toBeTruthy();
   });
 
   it('should allow multiple items to be expanded simultaneously', () => {
     const fixture = TestBed.createComponent(SetOfItems);
+    fixture.componentInstance.multi = true;
+    fixture.detectChanges();
+
     const panels = fixture.debugElement.queryAll(By.css('.mat-expansion-panel'));
+    const panelInstances = fixture.componentInstance.panels.toArray();
 
-    fixture.componentInstance.multi = true;
-    fixture.componentInstance.firstPanelExpanded = true;
-    fixture.componentInstance.secondPanelExpanded = true;
+    panelInstances[0].expanded = true;
+    panelInstances[1].expanded = true;
     fixture.detectChanges();
     expect(panels[0].classes['mat-expanded']).toBeTruthy();
     expect(panels[1].classes['mat-expanded']).toBeTruthy();
   });
 
   it('should expand or collapse all enabled items', () => {
     const fixture = TestBed.createComponent(SetOfItems);
+    fixture.detectChanges();
+
     const panels = fixture.debugElement.queryAll(By.css('.mat-expansion-panel'));
 
     fixture.componentInstance.multi = true;
-    fixture.componentInstance.secondPanelExpanded = true;
+    fixture.componentInstance.panels.toArray()[1].expanded = true;
     fixture.detectChanges();
     expect(panels[0].classes['mat-expanded']).toBeFalsy();
     expect(panels[1].classes['mat-expanded']).toBeTruthy();
@@ -70,10 +92,12 @@ describe('MatAccordion', () => {
 
   it('should not expand or collapse disabled items', () => {
     const fixture = TestBed.createComponent(SetOfItems);
+    fixture.detectChanges();
+
     const panels = fixture.debugElement.queryAll(By.css('.mat-expansion-panel'));
 
     fixture.componentInstance.multi = true;
-    fixture.componentInstance.secondPanelDisabled = true;
+    fixture.componentInstance.panels.toArray()[1].disabled = true;
     fixture.detectChanges();
     fixture.componentInstance.accordion.openAll();
     fixture.detectChanges();
@@ -93,27 +117,107 @@ describe('MatAccordion', () => {
 
     expect(innerPanel.accordion).not.toBe(outerPanel.accordion);
   });
+
+  it('should move focus to the next header when pressing the down arrow', () => {
+    const fixture = TestBed.createComponent(SetOfItems);
+    fixture.detectChanges();
+
+    const headerElements = fixture.debugElement.queryAll(By.css('mat-expansion-panel-header'));
+    const headers = fixture.componentInstance.headers.toArray();
+
+    focusMonitor.focusVia(headerElements[0].nativeElement, 'keyboard');
+    headers.forEach(header => spyOn(header, 'focus'));
+
+    // Stop at the second-last header so focus doesn't wrap around.
+    for (let i = 0; i < headerElements.length - 1; i++) {
+      dispatchKeyboardEvent(headerElements[i].nativeElement, 'keydown', DOWN_ARROW);
+      fixture.detectChanges();
+      expect(headers[i + 1].focus).toHaveBeenCalledTimes(1);
+    }
+  });
+
+  it('should move focus to the next header when pressing the up arrow', () => {
+    const fixture = TestBed.createComponent(SetOfItems);
+    fixture.detectChanges();
+
+    const headerElements = fixture.debugElement.queryAll(By.css('mat-expansion-panel-header'));
+    const headers = fixture.componentInstance.headers.toArray();
+
+    focusMonitor.focusVia(headerElements[headerElements.length - 1].nativeElement, 'keyboard');
+    headers.forEach(header => spyOn(header, 'focus'));
+
+    // Stop before the first header
+    for (let i = headers.length - 1; i > 0; i--) {
+      dispatchKeyboardEvent(headerElements[i].nativeElement, 'keydown', UP_ARROW);
+      fixture.detectChanges();
+      expect(headers[i - 1].focus).toHaveBeenCalledTimes(1);
+    }
+  });
+
+  it('should skip disabled items when moving focus with the keyboard', () => {
+    const fixture = TestBed.createComponent(SetOfItems);
+    fixture.detectChanges();
+
+    const headerElements = fixture.debugElement.queryAll(By.css('mat-expansion-panel-header'));
+    const panels = fixture.componentInstance.panels.toArray();
+    const headers = fixture.componentInstance.headers.toArray();
+
+    focusMonitor.focusVia(headerElements[0].nativeElement, 'keyboard');
+    headers.forEach(header => spyOn(header, 'focus'));
+    panels[1].disabled = true;
+    fixture.detectChanges();
+
+    dispatchKeyboardEvent(headerElements[0].nativeElement, 'keydown', DOWN_ARROW);
+    fixture.detectChanges();
+
+    expect(headers[1].focus).not.toHaveBeenCalled();
+    expect(headers[2].focus).toHaveBeenCalledTimes(1);
+  });
+
+  it('should focus the first header when pressing the home key', () => {
+    const fixture = TestBed.createComponent(SetOfItems);
+    fixture.detectChanges();
+
+    const headerElements = fixture.debugElement.queryAll(By.css('mat-expansion-panel-header'));
+    const headers = fixture.componentInstance.headers.toArray();
+
+    headers.forEach(header => spyOn(header, 'focus'));
+    dispatchKeyboardEvent(headerElements[headerElements.length - 1].nativeElement, 'keydown', HOME);
+    fixture.detectChanges();
+
+    expect(headers[0].focus).toHaveBeenCalledTimes(1);
+  });
+
+  it('should focus the last header when pressing the end key', () => {
+    const fixture = TestBed.createComponent(SetOfItems);
+    fixture.detectChanges();
+
+    const headerElements = fixture.debugElement.queryAll(By.css('mat-expansion-panel-header'));
+    const headers = fixture.componentInstance.headers.toArray();
+
+    headers.forEach(header => spyOn(header, 'focus'));
+    dispatchKeyboardEvent(headerElements[0].nativeElement, 'keydown', END);
+    fixture.detectChanges();
+
+    expect(headers[headers.length - 1].focus).toHaveBeenCalledTimes(1);
+  });
+
 });
 
 
 @Component({template: `
   <mat-accordion [multi]="multi">
-    <mat-expansion-panel [expanded]="firstPanelExpanded">
-      <mat-expansion-panel-header>Summary</mat-expansion-panel-header>
-      <p>Content</p>
-    </mat-expansion-panel>
-    <mat-expansion-panel [expanded]="secondPanelExpanded" [disabled]="secondPanelDisabled">
-      <mat-expansion-panel-header>Summary</mat-expansion-panel-header>
+    <mat-expansion-panel *ngFor="let i of [0, 1, 2, 3]">
+      <mat-expansion-panel-header>Summary {{i}}</mat-expansion-panel-header>
       <p>Content</p>
     </mat-expansion-panel>
   </mat-accordion>`})
 class SetOfItems {
   @ViewChild(MatAccordion) accordion: MatAccordion;
+  @ViewChildren(MatExpansionPanel) panels: QueryList<MatExpansionPanel>;
+  @ViewChildren(MatExpansionPanelHeader) headers: QueryList<MatExpansionPanelHeader>;
 
   multi: boolean = false;
-  firstPanelExpanded: boolean = false;
-  secondPanelExpanded: boolean = false;
-  secondPanelDisabled: boolean = false;
 }
 
 @Component({template: `

src/lib/expansion/accordion.ts

@@ -6,37 +6,71 @@
  * found in the LICENSE file at https://angular.io/license
  */
 
-import {Directive, Input} from '@angular/core';
+import {Directive, Input, ContentChildren, QueryList, AfterContentInit} from '@angular/core';
 import {coerceBooleanProperty} from '@angular/cdk/coercion';
 import {CdkAccordion} from '@angular/cdk/accordion';
-
-/** MatAccordion's display modes. */
-export type MatAccordionDisplayMode = 'default' | 'flat';
+import {FocusKeyManager} from '@angular/cdk/a11y';
+import {HOME, END} from '@angular/cdk/keycodes';
+import {MAT_ACCORDION, MatAccordionBase, MatAccordionDisplayMode} from './accordion-base';
+import {MatExpansionPanelHeader} from './expansion-panel-header';
 
 /**
  * Directive for a Material Design Accordion.
  */
 @Directive({
   selector: 'mat-accordion',
   exportAs: 'matAccordion',
+  providers: [{
+    provide: MAT_ACCORDION,
+    useExisting: MatAccordion
+  }],
   host: {
     class: 'mat-accordion'
   }
 })
-export class MatAccordion extends CdkAccordion {
+export class MatAccordion extends CdkAccordion implements MatAccordionBase, AfterContentInit {
+  private _keyManager: FocusKeyManager<MatExpansionPanelHeader>;
+
+  @ContentChildren(MatExpansionPanelHeader, {descendants: true})
+  _headers: QueryList<MatExpansionPanelHeader>;
+
   /** Whether the expansion indicator should be hidden. */
   @Input()
   get hideToggle(): boolean { return this._hideToggle; }
   set hideToggle(show: boolean) { this._hideToggle = coerceBooleanProperty(show); }
   private _hideToggle: boolean = false;
 
   /**
-   * The display mode used for all expansion panels in the accordion. Currently two display
+   * Display mode used for all expansion panels in the accordion. Currently two display
    * modes exist:
    *  default - a gutter-like spacing is placed around any expanded panel, placing the expanded
    *     panel at a different elevation from the rest of the accordion.
    *  flat - no spacing is placed around expanded panels, showing all panels at the same
    *     elevation.
    */
   @Input() displayMode: MatAccordionDisplayMode = 'default';
+
+  ngAfterContentInit() {
+    this._keyManager = new FocusKeyManager(this._headers).withWrap();
+  }
+
+  /** Handles keyboard events coming in from the panel headers. */
+  _handleHeaderKeydown(event: KeyboardEvent) {
+    const {keyCode} = event;
+    const manager = this._keyManager;
+
+    if (keyCode === HOME) {
+      manager.setFirstItemActive();
+      event.preventDefault();
+    } else if (keyCode === END) {
+      manager.setLastItemActive();
+      event.preventDefault();
+    } else {
+      this._keyManager.onKeydown(event);
+    }
+  }
+
+  _handleHeaderFocus(header: MatExpansionPanelHeader) {
+    this._keyManager.updateActiveItem(header);
+  }
 }