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fix(material/expansion-panel): Prevent focus issue during collapse animation #27684

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fix(material/expansion-panel): Prevent focus issue during collapse animation #27684

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20 changes: 16 additions & 4 deletions src/material/expansion/expansion-panel-header.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -7,7 +7,7 @@
*/

import {FocusableOption, FocusMonitor, FocusOrigin} from '@angular/cdk/a11y';
import {ENTER, hasModifierKey, SPACE} from '@angular/cdk/keycodes';
import {ENTER, hasModifierKey, SPACE, TAB} from '@angular/cdk/keycodes';
import {
AfterViewInit,
Attribute,
Expand Down Expand Up @@ -179,6 +179,13 @@ export class MatExpansionPanelHeader
return null;
}

/** Handle default for keydown event. */
private _handleDefaultKeydown(event: KeyboardEvent) {
if (this.panel.accordion) {
this.panel.accordion._handleHeaderKeydown(event);
}
}

/** Handle keydown event calling to toggle() if appropriate. */
_keydown(event: KeyboardEvent) {
switch (event.keyCode) {
Expand All @@ -191,10 +198,15 @@ export class MatExpansionPanelHeader
}

break;
default:
if (this.panel.accordion) {
this.panel.accordion._handleHeaderKeydown(event);
case TAB:
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I don't think that preventing users from tabbing is the right way to solve this issue. E.g. one could trigger it by clicking quickly as well. Instead we should not allow the panel to be toggled while an animation is running.

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The primary issue is that when a panel collapses, we expect the focus to smoothly transition to the next element when we press the tab key. However, if someone quickly presses the tab key during the collapse animation, the body panel isn't hidden fast enough, leading to an incorrect focus allocation, which causes some problems.

the collapse animation state:

state('collapsed, void', style({height: '0px', visibility: 'hidden'})),)

To address this, we can implement a solution where the panel animation happens rapidly while it's in the middle of collapsing when using the tab key. This adjustment ensures that the focus behaves correctly. If you have further thoughts, please feel free to share them.

if (this.panel.collapsingAnimation) {
this.panel._body.nativeElement.setAttribute('style', 'visibility: hidden');
}
this._handleDefaultKeydown(event);

break;
default:
this._handleDefaultKeydown(event);

return;
}
Expand Down
1 change: 1 addition & 0 deletions src/material/expansion/expansion-panel.html
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Original file line number Diff line number Diff line change
Expand Up @@ -2,6 +2,7 @@
<div class="mat-expansion-panel-content"
role="region"
[@bodyExpansion]="_getExpandedState()"
(@bodyExpansion.start)="_bodyAnimationStart($event)"
(@bodyExpansion.done)="_bodyAnimationDone.next($event)"
[attr.aria-labelledby]="_headerId"
[id]="id"
Expand Down
14 changes: 14 additions & 0 deletions src/material/expansion/expansion-panel.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -104,6 +104,12 @@ export class MatExpansionPanel
private _document: Document;
private _hideToggle = false;
private _togglePosition: MatAccordionTogglePosition;
private _collapsingAnimation = false;

/** whether the element is currently undergoing the collapsing animation */
get collapsingAnimation(): boolean {
return this._collapsingAnimation;
}

/** Whether the toggle indicator should be hidden. */
@Input()
Expand Down Expand Up @@ -174,6 +180,7 @@ export class MatExpansionPanel
}),
)
.subscribe(event => {
this._collapsingAnimation = false;
if (event.fromState !== 'void') {
if (event.toState === 'expanded') {
this.afterExpand.emit();
Expand All @@ -188,6 +195,13 @@ export class MatExpansionPanel
}
}

/** Check and determine if the element is currently undergoing a collapsing animation. */
_bodyAnimationStart(event: AnimationEvent) {
if (event.toState === 'collapsed') {
this._collapsingAnimation = true;
}
}

/** Determines whether the expansion panel should have spacing between it and its siblings. */
_hasSpacing(): boolean {
if (this.accordion) {
Expand Down