fix(accordion-group): skip initial animation

core/src/components/accordion/accordion.tsx

@@ -38,7 +38,40 @@ const enum AccordionState {
 })
 export class Accordion implements ComponentInterface {
   private accordionGroupEl?: HTMLIonAccordionGroupElement | null;
-  private updateListener = () => this.updateState(false);
+  private accordionGroupUpdateHandler = () => {
+    /**
+     * Determine if this update will cause an actual state change.
+     * We only want to mark as "interacted" if the state is changing.
+     */
+    const accordionGroup = this.accordionGroupEl;
+    if (accordionGroup) {
+      const value = accordionGroup.value;
+      const accordionValue = this.value;
+      const shouldExpand = Array.isArray(value) ? value.includes(accordionValue) : value === accordionValue;
+      const isExpanded = this.state === AccordionState.Expanded || this.state === AccordionState.Expanding;
+      const stateWillChange = shouldExpand !== isExpanded;
+
+      /**
+       * Only mark as interacted if:
+       * 1. This is not the first update we've received with a defined value
+       * 2. The state is actually changing (prevents redundant updates from enabling animations)
+       */
+      if (this.hasReceivedFirstUpdate && stateWillChange) {
+        this.hasInteracted = true;
+      }
+
+      /**
+       * Only count this as the first update if the group value is defined.
+       * This prevents the initial undefined value from the group's componentDidLoad
+       * from being treated as the first real update.
+       */
+      if (value !== undefined) {
+        this.hasReceivedFirstUpdate = true;
+      }
+    }
+
+    this.updateState();
+  };
   private contentEl: HTMLDivElement | undefined;
   private contentElWrapper: HTMLDivElement | undefined;
   private headerEl: HTMLDivElement | undefined;
@@ -50,6 +83,25 @@ export class Accordion implements ComponentInterface {
   @State() state: AccordionState = AccordionState.Collapsed;
   @State() isNext = false;
   @State() isPrevious = false;
+  /**
+   * Tracks whether a user-initiated interaction has occurred.
+   * Animations are disabled until the first interaction happens.
+   * This prevents the accordion from animating when it's programmatically
+   * set to an expanded or collapsed state on initial load.
+   */
+  @State() hasInteracted = false;
+
+  /**
+   * Tracks if this accordion has ever been expanded.
+   * Used to prevent the first expansion from animating.
+   */
+  private hasEverBeenExpanded = false;
+
+  /**
+   * Tracks if this accordion has received its first update from the group.
+   * Used to distinguish initial programmatic sets from user interactions.
+   */
+  private hasReceivedFirstUpdate = false;
 
   /**
    * The value of the accordion. Defaults to an autogenerated
@@ -88,15 +140,15 @@ export class Accordion implements ComponentInterface {
   connectedCallback() {
     const accordionGroupEl = (this.accordionGroupEl = this.el?.closest('ion-accordion-group'));
     if (accordionGroupEl) {
-      this.updateState(true);
-      addEventListener(accordionGroupEl, 'ionValueChange', this.updateListener);
+      this.updateState();
+      addEventListener(accordionGroupEl, 'ionValueChange', this.accordionGroupUpdateHandler);
     }
   }
 
   disconnectedCallback() {
     const accordionGroupEl = this.accordionGroupEl;
     if (accordionGroupEl) {
-      removeEventListener(accordionGroupEl, 'ionValueChange', this.updateListener);
+      removeEventListener(accordionGroupEl, 'ionValueChange', this.accordionGroupUpdateHandler);
     }
   }
 
@@ -212,10 +264,16 @@ export class Accordion implements ComponentInterface {
     ionItem.appendChild(iconEl);
   };
 
-  private expandAccordion = (initialUpdate = false) => {
+  private expandAccordion = () => {
     const { contentEl, contentElWrapper } = this;
-    if (initialUpdate || contentEl === undefined || contentElWrapper === undefined) {
+
+    /**
+     * If the content elements aren't available yet, just set the state.
+     * This happens on initial render before the DOM is ready.
+     */
+    if (contentEl === undefined || contentElWrapper === undefined) {
       this.state = AccordionState.Expanded;
+      this.hasEverBeenExpanded = true;
       return;
     }
 
@@ -227,6 +285,12 @@ export class Accordion implements ComponentInterface {
       cancelAnimationFrame(this.currentRaf);
     }
 
+    /**
+     * Mark that this accordion has been expanded at least once.
+     * This allows subsequent expansions to animate.
+     */
+    this.hasEverBeenExpanded = true;
+
     if (this.shouldAnimate()) {
       raf(() => {
         this.state = AccordionState.Expanding;
@@ -247,9 +311,14 @@ export class Accordion implements ComponentInterface {
     }
   };
 
-  private collapseAccordion = (initialUpdate = false) => {
+  private collapseAccordion = () => {
     const { contentEl } = this;
-    if (initialUpdate || contentEl === undefined) {
+
+    /**
+     * If the content element isn't available yet, just set the state.
+     * This happens on initial render before the DOM is ready.
+     */
+    if (contentEl === undefined) {
       this.state = AccordionState.Collapsed;
       return;
     }
@@ -291,6 +360,19 @@ export class Accordion implements ComponentInterface {
    * of what is set in the config.
    */
   private shouldAnimate = () => {
+    /**
+     * Don't animate until after the first user interaction.
+     * This prevents animations on initial load when accordions
+     * start in an expanded or collapsed state programmatically.
+     *
+     * Additionally, don't animate the very first expansion even if
+     * hasInteracted is true. This handles edge cases like React StrictMode
+     * where effects run twice and might incorrectly mark as interacted.
+     */
+    if (!this.hasInteracted || !this.hasEverBeenExpanded) {
+      return false;
+    }
+
     if (typeof (window as any) === 'undefined') {
       return false;
     }
@@ -312,7 +394,7 @@ export class Accordion implements ComponentInterface {
     return true;
   };
 
-  private updateState = async (initialUpdate = false) => {
+  private updateState = async () => {
     const accordionGroup = this.accordionGroupEl;
     const accordionValue = this.value;
 
@@ -325,10 +407,10 @@ export class Accordion implements ComponentInterface {
     const shouldExpand = Array.isArray(value) ? value.includes(accordionValue) : value === accordionValue;
 
     if (shouldExpand) {
-      this.expandAccordion(initialUpdate);
+      this.expandAccordion();
       this.isNext = this.isPrevious = false;
     } else {
-      this.collapseAccordion(initialUpdate);
+      this.collapseAccordion();
 
       /**
        * When using popout or inset,
@@ -386,6 +468,12 @@ export class Accordion implements ComponentInterface {
 
     if (disabled || readonly) return;
 
+    /**
+     * Mark that the user has interacted with the accordion.
+     * This enables animations for all future state changes.
+     */
+    this.hasInteracted = true;
+
     if (accordionGroupEl) {
       /**
        * Because the accordion group may or may

core/src/components/accordion/test/accordion.spec.ts

@@ -200,6 +200,87 @@ it('should set default values if not provided', async () => {
   expect(accordion.classList.contains('accordion-collapsed')).toEqual(false);
 });
 
+it('should not animate when initial value is set before load', async () => {
+  const page = await newSpecPage({
+    components: [Item, Accordion, AccordionGroup],
+  });
+
+  const accordionGroup = page.doc.createElement('ion-accordion-group');
+  accordionGroup.innerHTML = `
+    <ion-accordion value="first">
+      <ion-item slot="header">Label</ion-item>
+      <div slot="content">Content</div>
+    </ion-accordion>
+    <ion-accordion value="second">
+      <ion-item slot="header">Label</ion-item>
+      <div slot="content">Content</div>
+    </ion-accordion>
+  `;
+
+  accordionGroup.value = 'first';
+  page.body.appendChild(accordionGroup);
+
+  await page.waitForChanges();
+
+  const firstAccordion = accordionGroup.querySelector('ion-accordion[value="first"]')!;
+
+  expect(firstAccordion.classList.contains('accordion-expanded')).toEqual(true);
+  expect(firstAccordion.classList.contains('accordion-expanding')).toEqual(false);
+});
+
+it('should not animate when initial value is set after load', async () => {
+  const page = await newSpecPage({
+    components: [Item, Accordion, AccordionGroup],
+  });
+
+  const accordionGroup = page.doc.createElement('ion-accordion-group');
+  accordionGroup.innerHTML = `
+    <ion-accordion value="first">
+      <ion-item slot="header">Label</ion-item>
+      <div slot="content">Content</div>
+    </ion-accordion>
+    <ion-accordion value="second">
+      <ion-item slot="header">Label</ion-item>
+      <div slot="content">Content</div>
+    </ion-accordion>
+  `;
+
+  page.body.appendChild(accordionGroup);
+  await page.waitForChanges();
+
+  accordionGroup.value = 'first';
+  await page.waitForChanges();
+
+  const firstAccordion = accordionGroup.querySelector('ion-accordion[value="first"]')!;
+
+  expect(firstAccordion.classList.contains('accordion-expanded')).toEqual(true);
+  expect(firstAccordion.classList.contains('accordion-expanding')).toEqual(false);
+});
+
+it('should not have animated class on first expansion', async () => {
+  const page = await newSpecPage({
+    components: [Item, Accordion, AccordionGroup],
+    html: `
+      <ion-accordion-group>
+        <ion-accordion value="first">
+          <ion-item slot="header">Label</ion-item>
+          <div slot="content">Content</div>
+        </ion-accordion>
+      </ion-accordion-group>
+    `,
+  });
+
+  const accordionGroup = page.body.querySelector('ion-accordion-group')!;
+  const firstAccordion = page.body.querySelector('ion-accordion[value="first"]')!;
+
+  // First expansion should not have the animated class
+  accordionGroup.value = 'first';
+  await page.waitForChanges();
+
+  expect(firstAccordion.classList.contains('accordion-animated')).toEqual(false);
+  expect(firstAccordion.classList.contains('accordion-expanded')).toEqual(true);
+});
+
 // Verifies fix for https://github.com/ionic-team/ionic-framework/issues/27047
 it('should not have animated class when animated="false"', async () => {
   const page = await newSpecPage({

packages/react/test/base/src/App.tsx

@@ -37,6 +37,7 @@ import KeepContentsMounted from './pages/overlay-components/KeepContentsMounted'
 import OverlayComponents from './pages/overlay-components/OverlayComponents';
 import OverlayHooks from './pages/overlay-hooks/OverlayHooks';
 import ReorderGroup from './pages/ReorderGroup';
+import AccordionGroup from './pages/AccordionGroup';
 
 setupIonicReact();
 
@@ -69,6 +70,7 @@ const App: React.FC = () => (
         <Route path="/icons" component={Icons} />
         <Route path="/inputs" component={Inputs} />
         <Route path="/reorder-group" component={ReorderGroup} />
+        <Route path="/accordion-group" component={AccordionGroup} />
       </IonRouterOutlet>
     </IonReactRouter>
   </IonApp>

packages/react/test/base/src/pages/AccordionGroup.tsx

@@ -0,0 +1,54 @@
+import { IonHeader, IonTitle, IonToolbar, IonPage, IonContent, IonAccordionGroup, IonAccordion, IonItem, IonLabel } from '@ionic/react';
+import { useEffect, useRef } from 'react';
+
+const AccordionGroup: React.FC = () =>  {
+  const accordionGroup = useRef<null | HTMLIonAccordionGroupElement>(null);
+
+  useEffect(() => {
+    if (!accordionGroup.current) {
+      return;
+    }
+
+    accordionGroup.current.value = ['first', 'third'];
+  }, []);
+
+  return (
+    <IonPage>
+      <IonHeader>
+        <IonToolbar>
+          <IonTitle>Accordion Group</IonTitle>
+        </IonToolbar>
+      </IonHeader>
+      <IonContent>
+        <IonAccordionGroup ref={accordionGroup} multiple={true}>
+          <IonAccordion value="first">
+            <IonItem slot="header" color="light">
+              <IonLabel>First Accordion</IonLabel>
+            </IonItem>
+            <div className="ion-padding" slot="content">
+              First Content
+            </div>
+          </IonAccordion>
+          <IonAccordion value="second">
+            <IonItem slot="header" color="light">
+              <IonLabel>Second Accordion</IonLabel>
+            </IonItem>
+            <div className="ion-padding" slot="content">
+              Second Content
+            </div>
+          </IonAccordion>
+          <IonAccordion value="third">
+            <IonItem slot="header" color="light">
+              <IonLabel>Third Accordion</IonLabel>
+            </IonItem>
+            <div className="ion-padding" slot="content">
+              Third Content
+            </div>
+          </IonAccordion>
+        </IonAccordionGroup>
+      </IonContent>
+    </IonPage>
+  );
+};
+
+export default AccordionGroup;

packages/react/test/base/src/pages/Main.tsx

@@ -22,6 +22,9 @@ const Main: React.FC<MainProps> = () => {
       </IonHeader>
       <IonContent>
         <IonList>
+          <IonItem routerLink="/accordion-group">
+            <IonLabel>Accordion Group</IonLabel>
+          </IonItem>
           <IonItem routerLink="/overlay-hooks">
             <IonLabel>Overlay Hooks</IonLabel>
           </IonItem>