Keep one pane open in Angular Accordion component

22 Sep 20256 minutes to read

By default, all Accordion panels in the Syncfusion Angular Accordion component are collapsible in Single expand mode. The Accordion can be configured to always keep one panel in an expanded state, ensuring at least one content section remains visible. This is useful for scenarios requiring a default content display, such as highlighting key information or maintaining a consistent UI. This is applicable for Single expand mode.
The example below demonstrates an Accordion with one pane always expanded in Single mode.

import { NgModule } from '@angular/core'
import { BrowserModule } from '@angular/platform-browser'
import { AccordionModule } from '@syncfusion/ej2-angular-navigations'



import { Component, ViewChild } from '@angular/core';
import { AccordionComponent } from '@syncfusion/ej2-angular-navigations';
import {ExpandEventArgs, AccordionClickArgs} from '@syncfusion/ej2-navigations';

@Component({
imports: [
         AccordionModule
    ],


standalone: true,
    selector: 'app-container',
    template: `
    <ejs-accordion #element expandMode='Single' (expanding)="beforeExpand($event)" (clicked)="clicked($event)">
        <e-accordionitems>
          <e-accordionitem expanded='true'>
            <ng-template #header>
              <div>ASP.NET</div>
            </ng-template>
            <ng-template #content>
              <div>Microsoft ASP.NET is a set of technologies in the Microsoft .NET Framework for building Web applications and XML Web
                services. ASP.NET pages execute on the server and generate markup such as HTML, WML, or XML that is sent to a desktop
                or mobile browser. ASP.NET pages use a compiled,event-driven programming model that improves performance and enables
                the separation of application logic and user interface.</div>
            </ng-template>
          </e-accordionitem>
          <e-accordionitem>
            <ng-template #header>
              <div>ASP.NET MVC</div>
            </ng-template>
            <ng-template #content>
              <div>The Model-View-Controller (MVC) architectural pattern separates an application into three main components: the model,
                the view, and the controller. The ASP.NET MVC framework provides an alternative to the ASP.NET Web Forms pattern for
                creating Web applications. The ASP.NET MVC framework is a lightweight, highly testable presentation framework that
                (as with Web Forms-based applications) is integrated with existing ASP.NET features, such as master pages and membership-based
                authentication.
              </div>
            </ng-template>
          </e-accordionitem>
          <e-accordionitem>
            <ng-template #header>
              <div>JavaScript</div>
            </ng-template>
            <ng-template #content>
              <div>JavaScript (JS) is an interpreted computer programming language.It was originally implemented as part of web browsers
                so that client-side scripts could interact with the user, control the browser, communicate asynchronously, and alter
                the document content that was displayed.More recently, however, it has become common in both game development and
                the creation of desktop applications.</div>
            </ng-template>
          </e-accordionitem>
        </e-accordionitems>
    </ejs-accordion>
        `
})

export class AppComponent {
    @ViewChild('element') acrdnInstance?: AccordionComponent;
    public clickEle?: HTMLElement;
    public clicked(e: AccordionClickArgs) {
    this.clickEle = ((e.originalEvent as Event).target as Element).closest(
      '.e-acrdn-header'
    ) as HTMLElement;
  }
  public beforeExpand(e: ExpandEventArgs): void {
    const childrenArray = Array.from((this.acrdnInstance as AccordionComponent).element.children);
    const expandCount = childrenArray.filter(el => el.classList.contains('e-selected')).length;
    let ele = childrenArray.filter(el => el.classList.contains('e-selected'))[0];
    if (ele) {
      ele = ele.firstChild as Element;
    }
    if (expandCount === 1 && ele === this.clickEle) {
      e.cancel = true;
    }
  }
}
import { bootstrapApplication } from '@angular/platform-browser';
import { AppComponent } from './app.component';
import 'zone.js';
bootstrapApplication(AppComponent).catch((err) => console.error(err));