fix(cdk-experimental/listbox): initial listbox focus state

* The first option to receive focus in a listbox should be either the first focusable selected option or the first focusable option in the list if no focusable selected option exists.

Author: wagnermaciel

src/cdk-experimental/listbox/listbox.ts

@@ -7,14 +7,17 @@
  */
 
 import {
+  AfterViewInit,
   booleanAttribute,
   computed,
   contentChildren,
   Directive,
+  effect,
   ElementRef,
   inject,
   input,
   model,
+  signal,
 } from '@angular/core';
 import {ListboxPattern, OptionPattern} from '../ui-patterns';
 import {Directionality} from '@angular/cdk/bidi';
@@ -29,9 +32,9 @@ import {_IdGenerator} from '@angular/cdk/a11y';
  *
  * ```html
  * <ul cdkListbox>
- *   <li cdkOption>Item 1</li>
- *   <li cdkOption>Item 2</li>
- *   <li cdkOption>Item 3</li>
+ *   <li [value]="1" cdkOption>Item 1</li>
+ *   <li [value]="2" cdkOption>Item 2</li>
+ *   <li [value]="3" cdkOption>Item 3</li>
  * </ul>
  * ```
  */
@@ -49,9 +52,10 @@ import {_IdGenerator} from '@angular/cdk/a11y';
     '[attr.aria-activedescendant]': 'pattern.activedescendant()',
     '(keydown)': 'pattern.onKeydown($event)',
     '(pointerdown)': 'pattern.onPointerdown($event)',
+    '(focusin)': 'onFocus()',
   },
 })
-export class CdkListbox<V> {
+export class CdkListbox<V> implements AfterViewInit {
   /** The directionality (LTR / RTL) context for the application (or a subtree of it). */
   private readonly _directionality = inject(Directionality);
 
@@ -105,6 +109,28 @@ export class CdkListbox<V> {
     items: this.items,
     textDirection: this.textDirection,
   });
+
+  /** Whether the listbox has received focus yet. */
+  private _touched = signal(false);
+
+  /** Whether the options in the listbox have been initialized. */
+  private _isViewInitialized = signal(false);
+
+  constructor() {
+    effect(() => {
+      if (this._isViewInitialized() && !this._touched()) {
+        this.pattern.setDefaultState();
+      }
+    });
+  }
+
+  ngAfterViewInit() {
+    this._isViewInitialized.set(true);
+  }
+
+  onFocus() {
+    this._touched.set(true);
+  }
 }
 
 /** A selectable option in a CdkListbox. */
@@ -133,6 +159,7 @@ export class CdkOption<V> {
   /** A unique identifier for the option. */
   protected id = computed(() => this._generatedId);
 
+  /** The value of the option. */
   protected value = input.required<V>();
 
   // TODO(wagnermaciel): See if we want to change how we handle this since textContent is not

src/cdk-experimental/ui-patterns/behaviors/list-focus/list-focus.ts

@@ -75,7 +75,7 @@ export class ListFocus<T extends ListFocusItem> {
 
   /** Returns the tabindex for the given item. */
   getItemTabindex(item: T): -1 | 0 {
-    if (this.inputs.disabled()) {
+    if (this.isListDisabled()) {
       return -1;
     }
     if (this.inputs.focusMode() === 'activedescendant') {

src/cdk-experimental/ui-patterns/listbox/listbox.spec.ts

@@ -67,7 +67,7 @@ describe('Listbox Pattern', () => {
     const options = signal<TestOption[]>([]);
     const listbox = getListbox({...inputs, items: options});
     options.set(getOptions(listbox, values));
-    return {listbox, options};
+    return {listbox, options: options()};
   }
 
   function getDefaultPatterns(inputs: Partial<TestInputs> = {}) {
@@ -266,7 +266,7 @@ describe('Listbox Pattern', () => {
           multi: signal(true),
         });
         listbox = patterns.listbox;
-        options = patterns.options();
+        options = patterns.options;
       });
 
       it('should select an option on Space', () => {
@@ -428,7 +428,7 @@ describe('Listbox Pattern', () => {
           selectionMode: signal('follow'),
         });
         listbox = patterns.listbox;
-        options = patterns.options();
+        options = patterns.options;
       });
 
       it('should select an option on navigation', () => {
@@ -563,9 +563,9 @@ describe('Listbox Pattern', () => {
   });
 
   describe('Pointer Events', () => {
-    function click(options: WritableSignal<TestOption[]>, index: number, mods?: ModifierKeys) {
+    function click(options: TestOption[], index: number, mods?: ModifierKeys) {
       return {
-        target: options()[index].element(),
+        target: options[index].element(),
         shiftKey: mods?.shift,
         ctrlKey: mods?.control,
       } as unknown as PointerEvent;
@@ -716,7 +716,7 @@ describe('Listbox Pattern', () => {
           skipDisabled: signal(false),
           selectionMode: signal('follow'),
         });
-        options()[2].disabled.set(true);
+        options[2].disabled.set(true);
         listbox.onPointerdown(click(options, 0));
         expect(listbox.inputs.value()).toEqual(['Apple']);
 
@@ -732,7 +732,7 @@ describe('Listbox Pattern', () => {
           skipDisabled: signal(true),
           selectionMode: signal('follow'),
         });
-        options()[2].disabled.set(true);
+        options[2].disabled.set(true);
         listbox.onPointerdown(click(options, 0));
         expect(listbox.inputs.value()).toEqual(['Apple']);
         listbox.onKeydown(down({control: true}));
@@ -785,4 +785,50 @@ describe('Listbox Pattern', () => {
       expect(listbox.inputs.value()).toEqual(['Apple', 'Banana', 'Blackberry', 'Blueberry']);
     });
   });
+
+  describe('#setDefaultState', () => {
+    it('should set the active index to the first option', () => {
+      const {listbox} = getDefaultPatterns();
+      listbox.setDefaultState();
+      expect(listbox.inputs.activeIndex()).toBe(0);
+    });
+
+    it('should set the active index to the first focusable option', () => {
+      const {listbox, options} = getDefaultPatterns({
+        skipDisabled: signal(true),
+      });
+      options[0].disabled.set(true);
+      listbox.setDefaultState();
+      expect(listbox.inputs.activeIndex()).toBe(1);
+    });
+
+    it('should set the active index to the first selected option', () => {
+      const {listbox} = getDefaultPatterns({
+        value: signal(['Banana']),
+        skipDisabled: signal(true),
+      });
+      listbox.setDefaultState();
+      expect(listbox.inputs.activeIndex()).toBe(2);
+    });
+
+    it('should set the active index to the first focusable selected option', () => {
+      const {listbox, options} = getDefaultPatterns({
+        value: signal(['Banana', 'Blackberry']),
+        skipDisabled: signal(true),
+      });
+      options[2].disabled.set(true);
+      listbox.setDefaultState();
+      expect(listbox.inputs.activeIndex()).toBe(3);
+    });
+
+    it('should set the active index to the first option if no selected option is focusable', () => {
+      const {listbox, options} = getDefaultPatterns({
+        value: signal(['Banana']),
+        skipDisabled: signal(true),
+      });
+      options[2].disabled.set(true);
+      listbox.setDefaultState();
+      expect(listbox.inputs.activeIndex()).toBe(0);
+    });
+  });
 });

src/cdk-experimental/ui-patterns/listbox/listbox.ts

@@ -281,6 +281,36 @@ export class ListboxPattern<V> {
     this._navigate(opts, () => this.typeahead.search(char));
   }
 
+  /**
+   * Sets the listbox to it's default initial state.
+   *
+   * Sets the active index of the listbox to the first focusable selected
+   * item if one exists. Otherwise, sets focus to the first focusable item.
+   *
+   * This method should be called once the listbox and it's options are properly initialized,
+   * meaning the ListboxPattern and OptionPatterns should have references to each other before this
+   * is called.
+   */
+  setDefaultState() {
+    let firstItem: OptionPattern<V> | null = null;
+
+    for (const item of this.inputs.items()) {
+      if (this.focusManager.isFocusable(item)) {
+        if (!firstItem) {
+          firstItem = item;
+        }
+        if (item.selected()) {
+          this.inputs.activeIndex.set(item.index());
+          return;
+        }
+      }
+    }
+
+    if (firstItem) {
+      this.inputs.activeIndex.set(firstItem.index());
+    }
+  }
+
   /**
    * Safely performs a navigation operation.
    *

src/components-examples/cdk-experimental/listbox/cdk-listbox/cdk-listbox-example.html

@@ -5,6 +5,15 @@
   <mat-checkbox [formControl]="readonly">Readonly</mat-checkbox>
   <mat-checkbox [formControl]="skipDisabled">Skip Disabled</mat-checkbox>
 
+  <mat-form-field subscriptSizing="dynamic" appearance="outline">
+    <mat-label>Selection</mat-label>
+    <mat-select [(value)]="selection" multiple>
+      @for (fruit of fruits; track fruit) {
+        <mat-option [value]="fruit">{{fruit}}</mat-option>
+      }
+    </mat-select>
+  </mat-form-field>
+
   <mat-form-field subscriptSizing="dynamic" appearance="outline">
     <mat-label>Disabled Options</mat-label>
     <mat-select [(value)]="disabledOptions" multiple>
@@ -42,6 +51,7 @@
 <!-- #docregion listbox -->
 <ul
   cdkListbox
+  [value]="selection"
   [wrap]="wrap.value"
   [multi]="multi.value"
   [readonly]="readonly.value"

src/components-examples/cdk-experimental/listbox/cdk-listbox/cdk-listbox-example.ts

@@ -27,6 +27,7 @@ export class CdkListboxExample {
   focusMode: 'roving' | 'activedescendant' = 'roving';
   selectionMode: 'explicit' | 'follow' = 'explicit';
 
+  selection: string[] = ['Banana', 'Blackberry'];
   disabledOptions: string[] = ['Banana', 'Cantaloupe'];
 
   wrap = new FormControl(true, {nonNullable: true});