fix(material/datepicker): update active date on focus

When a a date cell on the calendar recieves focus, set the active date
to that cell. This ensures that the active date matches the date with
browser focus.

Previously, we set the active date on keydown and click, but that was
problematic for screenreaders. That's because many screenreaders trigger
a focus event instead of a keydown event when using screenreader
specific navigation (VoiceOver, Chromevox, NVDA).

Addresses #23483

Author: zarend

src/material/datepicker/calendar-body.html

@@ -51,6 +51,7 @@
       [attr.aria-selected]="_isSelected(item.compareValue)"
       [attr.aria-current]="todayValue === item.compareValue ? 'date' : null"
       (click)="_cellClicked(item, $event)"
+      (focus)="_cellFocused(item, $event)"
       [style.width]="_cellWidth"
       [style.paddingTop]="_cellPadding"
       [style.paddingBottom]="_cellPadding">

src/material/datepicker/calendar-body.ts

@@ -122,6 +122,9 @@ export class MatCalendarBody implements OnChanges, OnDestroy {
   /** Emits when a new value is selected. */
   @Output() readonly selectedValueChange = new EventEmitter<MatCalendarUserEvent<number>>();
 
+  /** Emits when a new date becomes active. */
+  @Output() readonly activeValueChange = new EventEmitter<MatCalendarUserEvent<number>>();
+
   /** Emits when the preview has changed as a result of a user action. */
   @Output() readonly previewChange = new EventEmitter<
     MatCalendarUserEvent<MatCalendarCell | null>
@@ -153,6 +156,13 @@ export class MatCalendarBody implements OnChanges, OnDestroy {
     }
   }
 
+  /** Called when a cell is focused. */
+  _cellFocused(cell: MatCalendarCell, event: FocusEvent): void {
+    if (cell.enabled) {
+      this.activeValueChange.emit({value: cell.value, event});
+    }
+  }
+
   /** Returns whether a cell should be marked as selected. */
   _isSelected(value: number) {
     return this.startValue === value || this.endValue === value;

src/material/datepicker/month-view.html

@@ -24,6 +24,7 @@
          [labelMinRequiredCells]="3"
          [activeCell]="_dateAdapter.getDate(activeDate) - 1"
          (selectedValueChange)="_dateSelected($event)"
+         (activeValueChange)="_dateBecomesActive($event)"
          (previewChange)="_previewChanged($event)"
          (keyup)="_handleCalendarBodyKeyup($event)"
          (keydown)="_handleCalendarBodyKeydown($event)">

src/material/datepicker/month-view.ts

@@ -252,6 +252,17 @@ export class MatMonthView<D> implements AfterContentInit, OnChanges, OnDestroy {
     this._changeDetectorRef.markForCheck();
   }
 
+  _dateBecomesActive(event: MatCalendarUserEvent<number>) {
+    const date = event.value;
+    const activeYear = this._dateAdapter.getYear(this.activeDate);
+    const activeMonth = this._dateAdapter.getMonth(this.activeDate);
+    const activeDate = this._dateAdapter.createDate(activeYear, activeMonth, date);
+
+    if (!this._dateAdapter.sameDate(activeDate, this._activeDate)) {
+      this.activeDateChange.emit(activeDate);
+    }
+  }
+
   /** Handles keydown events on the calendar body when calendar is in month view. */
   _handleCalendarBodyKeydown(event: KeyboardEvent): void {
     // TODO(mmalerba): We currently allow keyboard navigation to disabled dates, but just prevent
@@ -329,6 +340,9 @@ export class MatMonthView<D> implements AfterContentInit, OnChanges, OnDestroy {
       this.activeDateChange.emit(this.activeDate);
     }
 
+    // Ensure the calendar body has the correct active cell.
+    this._changeDetectorRef.detectChanges();
+
     this._focusActiveCell();
     // Prevent unexpected default actions such as form submission.
     event.preventDefault();

src/material/datepicker/multi-year-view.html

@@ -11,6 +11,7 @@
          [cellAspectRatio]="4 / 7"
          [activeCell]="_getActiveCell()"
          (selectedValueChange)="_yearSelected($event)"
+         (activeValueChange)="_yearBecomesActive($event)"
          (keyup)="_handleCalendarBodyKeyup($event)"
          (keydown)="_handleCalendarBodyKeydown($event)">
   </tbody>

src/material/datepicker/multi-year-view.ts

@@ -218,6 +218,21 @@ export class MatMultiYearView<D> implements AfterContentInit, OnDestroy {
     );
   }
 
+  _yearBecomesActive(event: MatCalendarUserEvent<number>) {
+    const year = event.value;
+    let month = this._dateAdapter.getMonth(this.activeDate);
+    let daysInMonth = this._dateAdapter.getNumDaysInMonth(
+      this._dateAdapter.createDate(year, month, 1),
+    );
+    this.activeDateChange.emit(
+      this._dateAdapter.createDate(
+        year,
+        month,
+        Math.min(this._dateAdapter.getDate(this.activeDate), daysInMonth),
+      ),
+    );
+  }
+
   /** Handles keydown events on the calendar body when calendar is in multi-year view. */
   _handleCalendarBodyKeydown(event: KeyboardEvent): void {
     const oldActiveDate = this._activeDate;
@@ -278,6 +293,9 @@ export class MatMultiYearView<D> implements AfterContentInit, OnDestroy {
       this.activeDateChange.emit(this.activeDate);
     }
 
+    // Ensure the calendar body has the correct active cell.
+    this._changeDetectorRef.detectChanges();
+
     this._focusActiveCell();
     // Prevent unexpected default actions such as form submission.
     event.preventDefault();

src/material/datepicker/year-view.html

@@ -13,6 +13,7 @@
          [cellAspectRatio]="4 / 7"
          [activeCell]="_dateAdapter.getMonth(activeDate)"
          (selectedValueChange)="_monthSelected($event)"
+         (activeValueChange)="_monthBecomesActive($event)"
          (keyup)="_handleCalendarBodyKeyup($event)"
          (keydown)="_handleCalendarBodyKeydown($event)">
   </tbody>

src/material/datepicker/year-view.ts

@@ -198,6 +198,25 @@ export class MatYearView<D> implements AfterContentInit, OnDestroy {
     );
   }
 
+  /** Handles when a new month becomes active. */
+  _monthBecomesActive(event: MatCalendarUserEvent<number>) {
+    const month = event.value;
+    const normalizedDate = this._dateAdapter.createDate(
+      this._dateAdapter.getYear(this.activeDate),
+      month,
+      1,
+    );
+
+    const daysInMonth = this._dateAdapter.getNumDaysInMonth(normalizedDate);
+
+    this.activeDateChange.emit(
+      this._dateAdapter.createDate(
+        this._dateAdapter.getYear(this.activeDate),
+        month,
+        Math.min(this._dateAdapter.getDate(this.activeDate), daysInMonth),
+      ),
+    );
+  }
   /** Handles keydown events on the calendar body when calendar is in year view. */
   _handleCalendarBodyKeydown(event: KeyboardEvent): void {
     // TODO(mmalerba): We currently allow keyboard navigation to disabled dates, but just prevent
@@ -261,6 +280,9 @@ export class MatYearView<D> implements AfterContentInit, OnDestroy {
       this.activeDateChange.emit(this.activeDate);
     }
 
+    // Ensure the calendar body has the correct active cell.
+    this._changeDetectorRef.detectChanges();
+
     this._focusActiveCell();
     // Prevent unexpected default actions such as form submission.
     event.preventDefault();

tools/public_api_guard/material/datepicker.md

@@ -200,8 +200,10 @@ export class MatCalendar<D> implements AfterContentInit, AfterViewChecked, OnDes
 export class MatCalendarBody implements OnChanges, OnDestroy {
     constructor(_elementRef: ElementRef<HTMLElement>, _ngZone: NgZone);
     activeCell: number;
+    readonly activeValueChange: EventEmitter<MatCalendarUserEvent<number>>;
     cellAspectRatio: number;
     _cellClicked(cell: MatCalendarCell, event: MouseEvent): void;
+    _cellFocused(cell: MatCalendarCell, event: FocusEvent): void;
     _cellPadding: string;
     _cellWidth: string;
     comparisonEnd: number | null;
@@ -239,7 +241,7 @@ export class MatCalendarBody implements OnChanges, OnDestroy {
     startValue: number;
     todayValue: number;
     // (undocumented)
-    static ɵcmp: i0.ɵɵComponentDeclaration<MatCalendarBody, "[mat-calendar-body]", ["matCalendarBody"], { "label": "label"; "rows": "rows"; "todayValue": "todayValue"; "startValue": "startValue"; "endValue": "endValue"; "labelMinRequiredCells": "labelMinRequiredCells"; "numCols": "numCols"; "activeCell": "activeCell"; "isRange": "isRange"; "cellAspectRatio": "cellAspectRatio"; "comparisonStart": "comparisonStart"; "comparisonEnd": "comparisonEnd"; "previewStart": "previewStart"; "previewEnd": "previewEnd"; }, { "selectedValueChange": "selectedValueChange"; "previewChange": "previewChange"; }, never, never>;
+    static ɵcmp: i0.ɵɵComponentDeclaration<MatCalendarBody, "[mat-calendar-body]", ["matCalendarBody"], { "label": "label"; "rows": "rows"; "todayValue": "todayValue"; "startValue": "startValue"; "endValue": "endValue"; "labelMinRequiredCells": "labelMinRequiredCells"; "numCols": "numCols"; "activeCell": "activeCell"; "isRange": "isRange"; "cellAspectRatio": "cellAspectRatio"; "comparisonStart": "comparisonStart"; "comparisonEnd": "comparisonEnd"; "previewStart": "previewStart"; "previewEnd": "previewEnd"; }, { "selectedValueChange": "selectedValueChange"; "activeValueChange": "activeValueChange"; "previewChange": "previewChange"; }, never, never>;
     // (undocumented)
     static ɵfac: i0.ɵɵFactoryDeclaration<MatCalendarBody, never>;
 }
@@ -759,6 +761,8 @@ export class MatMonthView<D> implements AfterContentInit, OnChanges, OnDestroy {
     comparisonStart: D | null;
     // (undocumented)
     _dateAdapter: DateAdapter<D>;
+    // (undocumented)
+    _dateBecomesActive(event: MatCalendarUserEvent<number>): void;
     dateClass: MatCalendarCellClassFunction<D>;
     dateFilter: (date: D) => boolean;
     _dateSelected(event: MatCalendarUserEvent<number>): void;
@@ -831,6 +835,8 @@ export class MatMultiYearView<D> implements AfterContentInit, OnDestroy {
     readonly selectedChange: EventEmitter<D>;
     _selectedYear: number | null;
     _todayYear: number;
+    // (undocumented)
+    _yearBecomesActive(event: MatCalendarUserEvent<number>): void;
     _years: MatCalendarCell[][];
     readonly yearSelected: EventEmitter<D>;
     _yearSelected(event: MatCalendarUserEvent<number>): void;
@@ -907,6 +913,7 @@ export class MatYearView<D> implements AfterContentInit, OnDestroy {
     set maxDate(value: D | null);
     get minDate(): D | null;
     set minDate(value: D | null);
+    _monthBecomesActive(event: MatCalendarUserEvent<number>): void;
     _months: MatCalendarCell[][];
     readonly monthSelected: EventEmitter<D>;
     _monthSelected(event: MatCalendarUserEvent<number>): void;