fix(material/dialog): update aria-labelledby if title is swapped (#27609)

Currently the dialog assigns the ID of the title as the `aria-labelleledby` of the container, but it doesn't update it if the title is swapped out or removed.

These changes add a queue of possible IDs that the container can use as titles are being created or destroyed.

Fixes #27599.

(cherry picked from commit 642d886)

Author: crisbeto

src/cdk/dialog/dialog-container.ts

@@ -60,7 +60,7 @@ export function throwDialogContentAlreadyAttachedError() {
     '[attr.id]': '_config.id || null',
     '[attr.role]': '_config.role',
     '[attr.aria-modal]': '_config.ariaModal',
-    '[attr.aria-labelledby]': '_config.ariaLabel ? null : _ariaLabelledBy',
+    '[attr.aria-labelledby]': '_config.ariaLabel ? null : _ariaLabelledByQueue[0]',
     '[attr.aria-label]': '_config.ariaLabel',
     '[attr.aria-describedby]': '_config.ariaDescribedBy || null',
   },
@@ -87,8 +87,13 @@ export class CdkDialogContainer<C extends DialogConfig = DialogConfig>
    */
   _closeInteractionType: FocusOrigin | null = null;
 
-  /** ID of the element that should be considered as the dialog's label. */
-  _ariaLabelledBy: string | null;
+  /**
+   * Queue of the IDs of the dialog's label element, based on their definition order. The first
+   * ID will be used as the `aria-labelledby` value. We use a queue here to handle the case
+   * where there are two or more titles in the DOM at a time and the first one is destroyed while
+   * the rest are present.
+   */
+  _ariaLabelledByQueue: string[] = [];
 
   constructor(
     protected _elementRef: ElementRef,
@@ -101,8 +106,12 @@ export class CdkDialogContainer<C extends DialogConfig = DialogConfig>
     private _focusMonitor?: FocusMonitor,
   ) {
     super();
-    this._ariaLabelledBy = this._config.ariaLabelledBy || null;
+
     this._document = _document;
+
+    if (this._config.ariaLabelledBy) {
+      this._ariaLabelledByQueue.push(this._config.ariaLabelledBy);
+    }
   }
 
   protected _contentAttached() {

src/material/dialog/dialog-container.ts

@@ -145,7 +145,7 @@ function parseCssTime(time: string | number | undefined): number | null {
     '[attr.aria-modal]': '_config.ariaModal',
     '[id]': '_config.id',
     '[attr.role]': '_config.role',
-    '[attr.aria-labelledby]': '_config.ariaLabel ? null : _ariaLabelledBy',
+    '[attr.aria-labelledby]': '_config.ariaLabel ? null : _ariaLabelledByQueue[0]',
     '[attr.aria-label]': '_config.ariaLabel',
     '[attr.aria-describedby]': '_config.ariaDescribedBy || null',
     '[class._mat-animation-noopable]': '!_animationsEnabled',

src/material/dialog/dialog-content-directives.ts

@@ -11,6 +11,7 @@ import {
   ElementRef,
   Input,
   OnChanges,
+  OnDestroy,
   OnInit,
   Optional,
   SimpleChanges,
@@ -97,7 +98,7 @@ export class MatDialogClose implements OnInit, OnChanges {
     '[id]': 'id',
   },
 })
-export class MatDialogTitle implements OnInit {
+export class MatDialogTitle implements OnInit, OnDestroy {
   @Input() id: string = `mat-mdc-dialog-title-${dialogElementUid++}`;
 
   constructor(
@@ -115,10 +116,24 @@ export class MatDialogTitle implements OnInit {
 
     if (this._dialogRef) {
       Promise.resolve().then(() => {
-        const container = this._dialogRef._containerInstance;
+        // Note: we null check the queue, because there are some internal
+        // tests that are mocking out `MatDialogRef` incorrectly.
+        this._dialogRef._containerInstance?._ariaLabelledByQueue?.push(this.id);
+      });
+    }
+  }
+
+  ngOnDestroy() {
+    // Note: we null check the queue, because there are some internal
+    // tests that are mocking out `MatDialogRef` incorrectly.
+    const queue = this._dialogRef?._containerInstance?._ariaLabelledByQueue;
+
+    if (queue) {
+      Promise.resolve().then(() => {
+        const index = queue.indexOf(this.id);
 
-        if (container && !container._ariaLabelledBy) {
-          container._ariaLabelledBy = this.id;
+        if (index > -1) {
+          queue.splice(index, 1);
         }
       });
     }

src/material/dialog/dialog.spec.ts

@@ -1587,12 +1587,14 @@ describe('MDC-based MatDialog', () => {
 
   describe('dialog content elements', () => {
     let dialogRef: MatDialogRef<any>;
+    let hostInstance: ContentElementDialog | ComponentWithContentElementTemplateRef;
 
     describe('inside component dialog', () => {
       beforeEach(fakeAsync(() => {
         dialogRef = dialog.open(ContentElementDialog, {viewContainerRef: testViewContainerRef});
         viewContainerFixture.detectChanges();
         flush();
+        hostInstance = dialogRef.componentInstance;
       }));
 
       runContentElementTests();
@@ -1609,6 +1611,7 @@ describe('MDC-based MatDialog', () => {
 
         viewContainerFixture.detectChanges();
         flush();
+        hostInstance = fixture.componentInstance;
       }));
 
       runContentElementTests();
@@ -1682,6 +1685,49 @@ describe('MDC-based MatDialog', () => {
           .toBe(title.id);
       }));
 
+      it('should update the aria-labelledby attribute if two titles are swapped', fakeAsync(() => {
+        const container = overlayContainerElement.querySelector('mat-dialog-container')!;
+        let title = overlayContainerElement.querySelector('[mat-dialog-title]')!;
+
+        flush();
+        viewContainerFixture.detectChanges();
+
+        const previousId = title.id;
+        expect(title.id).toBeTruthy();
+        expect(container.getAttribute('aria-labelledby')).toBe(title.id);
+
+        hostInstance.shownTitle = 'second';
+        viewContainerFixture.detectChanges();
+        flush();
+        viewContainerFixture.detectChanges();
+        title = overlayContainerElement.querySelector('[mat-dialog-title]')!;
+
+        expect(title.id).toBeTruthy();
+        expect(title.id).not.toBe(previousId);
+        expect(container.getAttribute('aria-labelledby')).toBe(title.id);
+      }));
+
+      it('should update the aria-labelledby attribute if multiple titles are present and one is removed', fakeAsync(() => {
+        const container = overlayContainerElement.querySelector('mat-dialog-container')!;
+
+        hostInstance.shownTitle = 'all';
+        viewContainerFixture.detectChanges();
+        flush();
+        viewContainerFixture.detectChanges();
+
+        const titles = overlayContainerElement.querySelectorAll('[mat-dialog-title]');
+
+        expect(titles.length).toBe(3);
+        expect(container.getAttribute('aria-labelledby')).toBe(titles[0].id);
+
+        hostInstance.shownTitle = 'second';
+        viewContainerFixture.detectChanges();
+        flush();
+        viewContainerFixture.detectChanges();
+
+        expect(container.getAttribute('aria-labelledby')).toBe(titles[1].id);
+      }));
+
       it('should add correct css class according to given [align] input in [mat-dialog-actions]', () => {
         let actions = overlayContainerElement.querySelector('mat-dialog-actions')!;
 
@@ -2116,7 +2162,9 @@ class PizzaMsg {
 
 @Component({
   template: `
-    <h1 mat-dialog-title>This is the title</h1>
+    <h1 mat-dialog-title *ngIf="shouldShowTitle('first')">This is the first title</h1>
+    <h1 mat-dialog-title *ngIf="shouldShowTitle('second')">This is the second title</h1>
+    <h1 mat-dialog-title *ngIf="shouldShowTitle('third')">This is the third title</h1>
     <mat-dialog-content>Lorem ipsum dolor sit amet.</mat-dialog-content>
     <mat-dialog-actions align="end">
       <button mat-dialog-close>Close</button>
@@ -2130,12 +2178,20 @@ class PizzaMsg {
     </mat-dialog-actions>
   `,
 })
-class ContentElementDialog {}
+class ContentElementDialog {
+  shownTitle: 'first' | 'second' | 'third' | 'all' = 'first';
+
+  shouldShowTitle(name: string) {
+    return this.shownTitle === 'all' || this.shownTitle === name;
+  }
+}
 
 @Component({
   template: `
     <ng-template>
-      <h1 mat-dialog-title>This is the title</h1>
+      <h1 mat-dialog-title *ngIf="shouldShowTitle('first')">This is the first title</h1>
+      <h1 mat-dialog-title *ngIf="shouldShowTitle('second')">This is the second title</h1>
+      <h1 mat-dialog-title *ngIf="shouldShowTitle('third')">This is the third title</h1>
       <mat-dialog-content>Lorem ipsum dolor sit amet.</mat-dialog-content>
       <mat-dialog-actions align="end">
         <button mat-dialog-close>Close</button>
@@ -2152,6 +2208,12 @@ class ContentElementDialog {}
 })
 class ComponentWithContentElementTemplateRef {
   @ViewChild(TemplateRef) templateRef: TemplateRef<any>;
+
+  shownTitle: 'first' | 'second' | 'third' | 'all' = 'first';
+
+  shouldShowTitle(name: string) {
+    return this.shownTitle === 'all' || this.shownTitle === name;
+  }
 }
 
 @Component({template: '', providers: [MatDialog]})

src/material/legacy-dialog/dialog-container.ts

@@ -46,7 +46,7 @@ import {_MatDialogContainerBase, matDialogAnimations} from '@angular/material/di
     '[attr.aria-modal]': '_config.ariaModal',
     '[id]': '_config.id',
     '[attr.role]': '_config.role',
-    '[attr.aria-labelledby]': '_config.ariaLabel ? null : _ariaLabelledBy',
+    '[attr.aria-labelledby]': '_config.ariaLabel ? null : _ariaLabelledByQueue[0]',
     '[attr.aria-label]': '_config.ariaLabel',
     '[attr.aria-describedby]': '_config.ariaDescribedBy || null',
     '[@dialogContainer]': `_getAnimationState()`,

src/material/legacy-dialog/dialog-content-directives.ts

@@ -14,6 +14,7 @@ import {
   Optional,
   SimpleChanges,
   ElementRef,
+  OnDestroy,
 } from '@angular/core';
 import {MatLegacyDialog} from './dialog';
 import {MatLegacyDialogRef} from './dialog-ref';
@@ -106,7 +107,7 @@ export class MatLegacyDialogClose implements OnInit, OnChanges {
     '[id]': 'id',
   },
 })
-export class MatLegacyDialogTitle implements OnInit {
+export class MatLegacyDialogTitle implements OnInit, OnDestroy {
   /** Unique id for the dialog title. If none is supplied, it will be auto-generated. */
   @Input() id: string = `mat-dialog-title-${dialogElementUid++}`;
 
@@ -125,10 +126,24 @@ export class MatLegacyDialogTitle implements OnInit {
 
     if (this._dialogRef) {
       Promise.resolve().then(() => {
-        const container = this._dialogRef._containerInstance;
+        // Note: we null check the queue, because there are some internal
+        // tests that are mocking out `MatDialogRef` incorrectly.
+        this._dialogRef._containerInstance?._ariaLabelledByQueue?.push(this.id);
+      });
+    }
+  }
+
+  ngOnDestroy() {
+    // Note: we null check the queue, because there are some internal
+    // tests that are mocking out `MatDialogRef` incorrectly.
+    const queue = this._dialogRef?._containerInstance?._ariaLabelledByQueue;
+
+    if (queue) {
+      Promise.resolve().then(() => {
+        const index = queue.indexOf(this.id);
 
-        if (container && !container._ariaLabelledBy) {
-          container._ariaLabelledBy = this.id;
+        if (index > -1) {
+          queue.splice(index, 1);
         }
       });
     }

tools/public_api_guard/cdk/dialog.md

@@ -45,7 +45,7 @@ export type AutoFocusTarget = 'dialog' | 'first-tabbable' | 'first-heading';
 // @public
 export class CdkDialogContainer<C extends DialogConfig = DialogConfig> extends BasePortalOutlet implements OnDestroy {
     constructor(_elementRef: ElementRef, _focusTrapFactory: FocusTrapFactory, _document: any, _config: C, _interactivityChecker: InteractivityChecker, _ngZone: NgZone, _overlayRef: OverlayRef, _focusMonitor?: FocusMonitor | undefined);
-    _ariaLabelledBy: string | null;
+    _ariaLabelledByQueue: string[];
     attachComponentPortal<T>(portal: ComponentPortal<T>): ComponentRef<T>;
     // @deprecated
     attachDomPortal: (portal: DomPortal) => void;

tools/public_api_guard/material/dialog.md

@@ -274,11 +274,13 @@ export const enum MatDialogState {
 }
 
 // @public
-export class MatDialogTitle implements OnInit {
+export class MatDialogTitle implements OnInit, OnDestroy {
     constructor(_dialogRef: MatDialogRef<any>, _elementRef: ElementRef<HTMLElement>, _dialog: MatDialog);
     // (undocumented)
     id: string;
     // (undocumented)
+    ngOnDestroy(): void;
+    // (undocumented)
     ngOnInit(): void;
     // (undocumented)
     static ɵdir: i0.ɵɵDirectiveDeclaration<MatDialogTitle, "[mat-dialog-title], [matDialogTitle]", ["matDialogTitle"], { "id": { "alias": "id"; "required": false; }; }, {}, never, never, false, never>;

tools/public_api_guard/material/legacy-dialog.md

@@ -31,6 +31,7 @@ import { _MatDialogContainerBase as _MatLegacyDialogContainerBase } from '@angul
 import { MatDialogState as MatLegacyDialogState } from '@angular/material/dialog';
 import { NgZone } from '@angular/core';
 import { OnChanges } from '@angular/core';
+import { OnDestroy } from '@angular/core';
 import { OnInit } from '@angular/core';
 import { Overlay } from '@angular/cdk/overlay';
 import { OverlayContainer } from '@angular/cdk/overlay';
@@ -171,10 +172,12 @@ export class MatLegacyDialogRef<T, R = any> extends MatDialogRef<T, R> {
 export { MatLegacyDialogState }
 
 // @public @deprecated
-export class MatLegacyDialogTitle implements OnInit {
+export class MatLegacyDialogTitle implements OnInit, OnDestroy {
     constructor(_dialogRef: MatLegacyDialogRef<any>, _elementRef: ElementRef<HTMLElement>, _dialog: MatLegacyDialog);
     id: string;
     // (undocumented)
+    ngOnDestroy(): void;
+    // (undocumented)
     ngOnInit(): void;
     // (undocumented)
     static ɵdir: i0.ɵɵDirectiveDeclaration<MatLegacyDialogTitle, "[mat-dialog-title], [matDialogTitle]", ["matDialogTitle"], { "id": { "alias": "id"; "required": false; }; }, {}, never, never, false, never>;