fix(datetime): update active calendar display when value changes (#24244)

core/src/components/datetime/datetime.tsx

@@ -93,6 +93,12 @@ export class Datetime implements ComponentInterface {
   private minParts?: any;
   private maxParts?: any;
 
+  /**
+   * Duplicate reference to `activeParts` that does not trigger a re-render of the component.
+   * Allows caching an instance of the `activeParts` in between render cycles.
+   */
+  private activePartsClone!: DatetimeParts;
+
   @State() showMonthAndYear = false;
 
   @State() activeParts: DatetimeParts = {
@@ -291,6 +297,25 @@ export class Datetime implements ComponentInterface {
    */
   @Watch('value')
   protected valueChanged() {
+    if (this.hasValue()) {
+      /**
+       * Clones the value of the `activeParts` to the private clone, to update
+       * the date display on the current render cycle without causing another render.
+       *
+       * This allows us to update the current value's date/time display without
+       * refocusing or shifting the user's display (leaves the user in place).
+       */
+      const { month, day, year, hour, minute } = parseDate(this.value);
+      this.activePartsClone = {
+        ...this.activeParts,
+        month,
+        day,
+        year,
+        hour,
+        minute
+      }
+    }
+
     this.emitStyle();
     this.ionChange.emit({
       value: this.value
@@ -911,7 +936,8 @@ export class Datetime implements ComponentInterface {
       tzOffset,
       ampm: hour >= 12 ? 'pm' : 'am'
     }
-    this.activeParts = {
+
+    this.activePartsClone = this.activeParts = {
       month,
       day,
       year,
@@ -951,6 +977,10 @@ export class Datetime implements ComponentInterface {
     this.ionBlur.emit();
   }
 
+  private hasValue = () => {
+    return this.value != null && this.value !== '';
+  }
+
   private nextMonth = () => {
     const { calendarBodyRef } = this;
     if (!calendarBodyRef) { return; }
@@ -1135,7 +1165,7 @@ export class Datetime implements ComponentInterface {
           {getDaysOfMonth(month, year, this.firstDayOfWeek % 7).map((dateObject, index) => {
             const { day, dayOfWeek } = dateObject;
             const referenceParts = { month, day, year };
-            const { isActive, isToday, ariaLabel, ariaSelected, disabled } = getCalendarDayState(this.locale, referenceParts, this.activeParts, this.todayParts, this.minParts, this.maxParts, this.parsedDayValues);
+            const { isActive, isToday, ariaLabel, ariaSelected, disabled } = getCalendarDayState(this.locale, referenceParts, this.activePartsClone, this.todayParts, this.minParts, this.maxParts, this.parsedDayValues);
 
             return (
               <button
@@ -1213,21 +1243,22 @@ export class Datetime implements ComponentInterface {
     ampmItems: PickerColumnItem[],
     use24Hour: boolean
    ) {
-    const { color, workingParts } = this;
+    const { color, activePartsClone, workingParts } = this;
+
     return (
       <ion-picker-internal>
         <ion-picker-column-internal
           color={color}
-          value={workingParts.hour}
+          value={activePartsClone.hour}
           items={hoursItems}
           numericInput
           onIonChange={(ev: CustomEvent) => {
             this.setWorkingParts({
-              ...this.workingParts,
+              ...workingParts,
               hour: ev.detail.value
             });
             this.setActiveParts({
-              ...this.activeParts,
+              ...activePartsClone,
               hour: ev.detail.value
             });
 
@@ -1236,16 +1267,16 @@ export class Datetime implements ComponentInterface {
         ></ion-picker-column-internal>
         <ion-picker-column-internal
           color={color}
-          value={workingParts.minute}
+          value={activePartsClone.minute}
           items={minutesItems}
           numericInput
           onIonChange={(ev: CustomEvent) => {
             this.setWorkingParts({
-              ...this.workingParts,
+              ...workingParts,
               minute: ev.detail.value
             });
             this.setActiveParts({
-              ...this.activeParts,
+              ...activePartsClone,
               minute: ev.detail.value
             });
 
@@ -1254,19 +1285,19 @@ export class Datetime implements ComponentInterface {
         ></ion-picker-column-internal>
         { !use24Hour && <ion-picker-column-internal
           color={color}
-          value={workingParts.ampm}
+          value={activePartsClone.ampm}
           items={ampmItems}
           onIonChange={(ev: CustomEvent) => {
-            const hour = calculateHourFromAMPM(this.workingParts, ev.detail.value);
+            const hour = calculateHourFromAMPM(workingParts, ev.detail.value);
 
             this.setWorkingParts({
-              ...this.workingParts,
+              ...workingParts,
               ampm: ev.detail.value,
               hour
             });
 
             this.setActiveParts({
-              ...this.workingParts,
+              ...activePartsClone,
               ampm: ev.detail.value,
               hour
             });
@@ -1309,7 +1340,7 @@ export class Datetime implements ComponentInterface {
           }
         }}
       >
-        {getFormattedTime(this.workingParts, use24Hour)}
+        {getFormattedTime(this.activePartsClone, use24Hour)}
       </button>,
       <ion-popover
         alignment="center"