fix(cdk/a11y): support signals in ListKeyManager (angular#28757)

Updates the `ListKeyManager` to support passing in a signal. Also expands the type to allow readonly arrays.

Fixes angular#28710.

src/cdk/a11y/key-manager/list-key-manager.spec.ts

@@ -1,7 +1,7 @@
 import {DOWN_ARROW, END, HOME, LEFT_ARROW, RIGHT_ARROW, TAB, UP_ARROW} from '@angular/cdk/keycodes';
 import {createKeyboardEvent} from '../../testing/private';
-import {QueryList} from '@angular/core';
-import {fakeAsync, tick} from '@angular/core/testing';
+import {Component, QueryList, signal} from '@angular/core';
+import {TestBed, fakeAsync, tick} from '@angular/core/testing';
 import {take} from 'rxjs/operators';
 import {FocusOrigin} from '../focus-monitor/focus-monitor';
 import {ActiveDescendantKeyManager} from './activedescendant-key-manager';
@@ -106,6 +106,33 @@ describe('Key managers', () => {
       expect(keyManager.activeItem).toBeNull();
     });
 
+    it('should maintain the active item when the signal-based items change', () => {
+      keyManager.destroy();
+
+      @Component({template: '', standalone: true})
+      class App {}
+
+      const fixture = TestBed.createComponent(App);
+      fixture.detectChanges();
+      const items = signal([
+        new FakeFocusable('one'),
+        new FakeFocusable('two'),
+        new FakeFocusable('three'),
+      ]);
+
+      keyManager = new ListKeyManager<FakeFocusable>(items, fixture.componentRef.injector);
+      keyManager.setFirstItemActive();
+      spyOn(keyManager, 'setActiveItem').and.callThrough();
+
+      expect(keyManager.activeItemIndex).toBe(0);
+      expect(keyManager.activeItem!.getLabel()).toBe('one');
+      items.update(current => [new FakeFocusable('zero'), ...current]);
+      fixture.detectChanges();
+
+      expect(keyManager.activeItemIndex).toBe(1);
+      expect(keyManager.activeItem!.getLabel()).toBe('one');
+    });
+
     describe('Key events', () => {
       it('should emit tabOut when the tab key is pressed', () => {
         const spy = jasmine.createSpy('tabOut spy');

src/cdk/a11y/key-manager/list-key-manager.ts

@@ -6,7 +6,7 @@
  * found in the LICENSE file at https://angular.io/license
  */
 
-import {QueryList} from '@angular/core';
+import {EffectRef, Injector, QueryList, Signal, effect, isSignal} from '@angular/core';
 import {Subject, Subscription} from 'rxjs';
 import {
   UP_ARROW,
@@ -54,6 +54,7 @@ export class ListKeyManager<T extends ListKeyManagerOption> {
   private _allowedModifierKeys: ListKeyManagerModifierKey[] = [];
   private _homeAndEnd = false;
   private _pageUpAndDown = {enabled: false, delta: 10};
+  private _effectRef: EffectRef | undefined;
 
   /**
    * Predicate function that can be used to check whether an item should be skipped
@@ -64,21 +65,25 @@ export class ListKeyManager<T extends ListKeyManagerOption> {
   // Buffer for the letters that the user has pressed when the typeahead option is turned on.
   private _pressedLetters: string[] = [];
 
-  constructor(private _items: QueryList<T> | T[]) {
+  constructor(items: QueryList<T> | T[] | readonly T[]);
+  constructor(items: Signal<T[]> | Signal<readonly T[]>, injector: Injector);
+  constructor(
+    private _items: QueryList<T> | T[] | readonly T[] | Signal<T[]> | Signal<readonly T[]>,
+    injector?: Injector,
+  ) {
     // We allow for the items to be an array because, in some cases, the consumer may
     // not have access to a QueryList of the items they want to manage (e.g. when the
     // items aren't being collected via `ViewChildren` or `ContentChildren`).
     if (_items instanceof QueryList) {
-      this._itemChangesSubscription = _items.changes.subscribe((newItems: QueryList<T>) => {
-        if (this._activeItem) {
-          const itemArray = newItems.toArray();
-          const newIndex = itemArray.indexOf(this._activeItem);
+      this._itemChangesSubscription = _items.changes.subscribe((newItems: QueryList<T>) =>
+        this._itemsChanged(newItems.toArray()),
+      );
+    } else if (isSignal(_items)) {
+      if (!injector && (typeof ngDevMode === 'undefined' || ngDevMode)) {
+        throw new Error('ListKeyManager constructed with a signal must receive an injector');
+      }
 
-          if (newIndex > -1 && newIndex !== this._activeItemIndex) {
-            this._activeItemIndex = newIndex;
-          }
-        }
-      });
+      this._effectRef = effect(() => this._itemsChanged(_items()), {injector});
     }
   }
 
@@ -144,12 +149,11 @@ export class ListKeyManager<T extends ListKeyManagerOption> {
    * @param debounceInterval Time to wait after the last keystroke before setting the active item.
    */
   withTypeAhead(debounceInterval: number = 200): this {
-    if (
-      (typeof ngDevMode === 'undefined' || ngDevMode) &&
-      this._items.length &&
-      this._items.some(item => typeof item.getLabel !== 'function')
-    ) {
-      throw Error('ListKeyManager items in typeahead mode must implement the `getLabel` method.');
+    if (typeof ngDevMode === 'undefined' || ngDevMode) {
+      const items = this._getItemsArray();
+      if (items.length > 0 && items.some(item => typeof item.getLabel !== 'function')) {
+        throw Error('ListKeyManager items in typeahead mode must implement the `getLabel` method.');
+      }
     }
 
     this._typeaheadSubscription.unsubscribe();
@@ -403,6 +407,7 @@ export class ListKeyManager<T extends ListKeyManagerOption> {
   destroy() {
     this._typeaheadSubscription.unsubscribe();
     this._itemChangesSubscription?.unsubscribe();
+    this._effectRef?.destroy();
     this._letterKeyStream.complete();
     this.tabOut.complete();
     this.change.complete();
@@ -470,7 +475,22 @@ export class ListKeyManager<T extends ListKeyManagerOption> {
   }
 
   /** Returns the items as an array. */
-  private _getItemsArray(): T[] {
+  private _getItemsArray(): T[] | readonly T[] {
+    if (isSignal(this._items)) {
+      return this._items();
+    }
+
     return this._items instanceof QueryList ? this._items.toArray() : this._items;
   }
+
+  /** Callback for when the items have changed. */
+  private _itemsChanged(newItems: T[] | readonly T[]) {
+    if (this._activeItem) {
+      const newIndex = newItems.indexOf(this._activeItem);
+
+      if (newIndex > -1 && newIndex !== this._activeItemIndex) {
+        this._activeItemIndex = newIndex;
+      }
+    }
+  }
 }

tools/public_api_guard/cdk/a11y.md

@@ -13,12 +13,14 @@ import { EventEmitter } from '@angular/core';
 import * as i0 from '@angular/core';
 import * as i1 from '@angular/cdk/observers';
 import { InjectionToken } from '@angular/core';
+import { Injector } from '@angular/core';
 import { NgZone } from '@angular/core';
 import { Observable } from 'rxjs';
 import { OnChanges } from '@angular/core';
 import { OnDestroy } from '@angular/core';
 import { Platform } from '@angular/cdk/platform';
 import { QueryList } from '@angular/core';
+import { Signal } from '@angular/core';
 import { SimpleChanges } from '@angular/core';
 import { Subject } from 'rxjs';
 
@@ -347,7 +349,8 @@ export class IsFocusableConfig {
 
 // @public
 export class ListKeyManager<T extends ListKeyManagerOption> {
-    constructor(_items: QueryList<T> | T[]);
+    constructor(items: QueryList<T> | T[] | readonly T[]);
+    constructor(items: Signal<T[]> | Signal<readonly T[]>, injector: Injector);
     get activeItem(): T | null;
     get activeItemIndex(): number | null;
     cancelTypeahead(): this;