feat(list): Add basic keyboard navigation to M3 list

PiperOrigin-RevId: 465533534

Author: material-web-copybara

list/lib/list.ts

@@ -6,17 +6,29 @@
 
 import {ARIARole} from '@material/web/types/aria';
 import {html, LitElement, PropertyValues, TemplateResult} from 'lit';
-import {queryAssignedElements} from 'lit/decorators';
+import {property, query, queryAssignedElements} from 'lit/decorators';
 
 import {ListItemInteractionEvent} from './listitem/constants';
 import {ListItem} from './listitem/list-item';
 
+const NAVIGATABLE_KEYS = {
+  ArrowDown: 'ArrowDown',
+  ArrowUp: 'ArrowUp',
+  Home: 'Home',
+  End: 'End',
+};
+
 /** @soyCompatible */
 export class List extends LitElement {
   static override shadowRootOptions:
       ShadowRootInit = {mode: 'open', delegatesFocus: true};
 
+  @property({type: Number}) listTabIndex: number = 0;
+
   items: ListItem[] = [];
+  activeListItem: ListItem|null = null;
+
+  @query('.md3-list') listRoot!: HTMLElement;
 
   @queryAssignedElements({flatten: true})
   protected assignedElements!: HTMLElement[]|null;
@@ -36,20 +48,76 @@ export class List extends LitElement {
   override render(): TemplateResult {
     return html`
       <ul class="md3-list"
-          tabindex="0"
+          tabindex=${this.listTabIndex}
           role=${this.getAriaRole()}
-          @list-item-interaction=${this.handleItemInteraction}>
+          @list-item-interaction=${this.handleItemInteraction}
+          @keydown=${this.handleKeydown}
+          >
         <slot></slot>
       </ul>
     `;
   }
 
+  handleKeydown(event: KeyboardEvent) {
+    if (Object.values(NAVIGATABLE_KEYS).indexOf(event.key) === -1) return;
+
+    if (event.key === NAVIGATABLE_KEYS.ArrowDown) {
+      event.preventDefault();
+      if (this.activeListItem) {
+        this.activeListItem = this.getNextItem(this.activeListItem);
+      } else {
+        this.activeListItem = this.getFirstItem();
+      }
+    }
+
+    if (event.key === NAVIGATABLE_KEYS.ArrowUp) {
+      event.preventDefault();
+      if (this.activeListItem) {
+        this.activeListItem = this.getPrevItem(this.activeListItem);
+      } else {
+        this.activeListItem = this.getLastItem();
+      }
+    }
+
+    if (event.key === NAVIGATABLE_KEYS.Home) {
+      event.preventDefault();
+      this.activeListItem = this.getFirstItem();
+    }
+
+    if (event.key === NAVIGATABLE_KEYS.End) {
+      event.preventDefault();
+      this.activeListItem = this.getLastItem();
+    }
+
+    if (!this.activeListItem) return;
+
+    for (const item of this.items) {
+      item.deactivate();
+    }
+
+    this.activeListItem.activate();
+  }
+
   handleItemInteraction(event: ListItemInteractionEvent) {
     if (event.detail.state.isSelected) {
       // TODO: manage selection state.
     }
   }
 
+  activateFirstItem() {
+    this.activeListItem = this.getFirstItem();
+    this.activeListItem.activate();
+  }
+
+  activateLastItem() {
+    this.activeListItem = this.getLastItem();
+    this.activeListItem.activate();
+  }
+
+  focusListRoot() {
+    this.listRoot.focus();
+  }
+
   /** Updates `this.items` based on slot elements in the DOM. */
   protected updateItems() {
     const elements = this.assignedElements || [];
@@ -64,4 +132,22 @@ export class List extends LitElement {
   private isListItem(element: Element): element is ListItem {
     return element.tagName.toLowerCase() === this.getListItemTagName();
   }
+
+  private getFirstItem(): ListItem {
+    return this.items[0];
+  }
+
+  private getLastItem(): ListItem {
+    return this.items[this.items.length - 1];
+  }
+
+  private getPrevItem(item: ListItem): ListItem {
+    const curIndex = this.items.indexOf(item);
+    return this.items[curIndex === 0 ? this.items.length - 1 : curIndex - 1];
+  }
+
+  private getNextItem(item: ListItem): ListItem {
+    const curIndex = this.items.indexOf(item);
+    return this.items[(curIndex + 1) % this.items.length];
+  }
 }

list/lib/listitem/list-item.ts

@@ -19,15 +19,18 @@ export class ListItem extends ActionElement {
   @property({type: String}) multiLineSupportingText = '';
   @property({type: String}) trailingSupportingText = '';
   @property({type: Boolean}) disabled = false;
+  @property({type: Number}) itemTabIndex = -1;
   @property({type: String}) headline = '';
   @query('md-ripple') ripple!: MdRipple;
+  @query('[data-query-md3-list-item]') listItemRoot!: HTMLElement;
 
   /** @soyTemplate */
   override render(): TemplateResult {
     return html`
       <li
-          tabindex="0"
+          tabindex=${this.itemTabIndex}
           role=${this.getAriaRole()}
+          data-query-md3-list-item
           class="md3-list-item ${classMap(this.getRenderClasses())}"
           @pointerdown=${this.handlePointerDown}
           @pointerenter=${this.handlePointerEnter}
@@ -166,4 +169,13 @@ export class ListItem extends ActionElement {
     // TODO(b/240124486): Replace with beginPress provided by action element.
     this.ripple.endPress();
   }
+
+  activate() {
+    this.itemTabIndex = 0;
+    this.listItemRoot.focus();
+  }
+
+  deactivate() {
+    this.itemTabIndex = -1;
+  }
 }

list/list-item_test.ts

@@ -0,0 +1,38 @@
+/**
+ * @license
+ * Copyright 2022 Google LLC
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+import './list-item';
+
+import {Environment} from '@material/web/testing/environment';
+import {html} from 'lit';
+
+const LIST_ITEM_TEMPLATE = html`
+     <md-list-item>One</md-list-item>
+ `;
+
+describe('list item tests', () => {
+  const env = new Environment();
+
+  it('`activate()` should focus the list item', async () => {
+    const listItem =
+        env.render(LIST_ITEM_TEMPLATE).querySelector('md-list-item')!;
+    await env.waitForStability();
+
+    listItem.activate();
+    expect(document.activeElement).toEqual(listItem);
+  });
+
+  it('`deactivate()` should set root tab index to -1', async () => {
+    const listItem =
+        env.render(LIST_ITEM_TEMPLATE).querySelector('md-list-item')!;
+    await env.waitForStability();
+
+    listItem.deactivate();
+    expect(listItem.shadowRoot!.querySelector('[tabindex]')!.getAttribute(
+               'tabindex'))
+        .toBe('-1');
+  });
+});

list/list_test.ts

@@ -27,4 +27,28 @@ describe('list tests', () => {
 
     expect(element.items.length).toBe(3);
   });
+
+  it('focusListRoot() should focus on the list element', async () => {
+    const list = env.render(LIST_TEMPLATE).querySelector('md-list')!;
+    await env.waitForStability();
+
+    list.focusListRoot();
+    expect(document.activeElement).toEqual(list);
+  });
+
+  it('activateFirstItem() should focus on the first list item', async () => {
+    const list = env.render(LIST_TEMPLATE).querySelector('md-list')!;
+    await env.waitForStability();
+
+    list.activateFirstItem();
+    expect(document.activeElement).toEqual(list.items[0]);
+  });
+
+  it('activateLastItem() should focus on the last list item', async () => {
+    const list = env.render(LIST_TEMPLATE).querySelector('md-list')!;
+    await env.waitForStability();
+
+    list.activateLastItem();
+    expect(document.activeElement).toEqual(list.items[list.items.length - 1]);
+  });
 });