How to toggle Angular material expansion panel programmatically

Question

I just started working on an Angular 4 project with material design.

I am currently working with the expansion component, the API states that a disabled expansion panel can't be toggled by the user, but can still be manipulated programmatically. I don't know however, how you can toggle your panel programmatically.

What is the preferred way in Angular to simulate this?

Answer 1

expanded is set to true to expand the expansion panel and set to false to close the expansion panel. In the following example, expansion panel is programmatically opened and closed. Please refer this link

TS file

import { Component } from '@angular/core';

/**
 * @title Expansion panel as accordion
 */
@Component({
    selector: 'expansion-steps-example',
    templateUrl: 'expansion-steps-example.html',
    styleUrls: ['expansion-steps-example.css']
})
export class ExpansionStepsExample {
    step = 0;

    setStep(index: number) {
        this.step = index;
    }

    nextStep() {
        this.step++;
    }

    prevStep() {
        this.step--;
    }
}

HTML file

<mat-accordion class="example-headers-align">
    <mat-expansion-panel [expanded]="step === 0" (opened)="setStep(0)" hideToggle="true">
        <mat-expansion-panel-header>
            <mat-panel-title>
                Personal data
            </mat-panel-title>
            <mat-panel-description>
                Type your name and age
                <mat-icon>account_circle</mat-icon>
            </mat-panel-description>
        </mat-expansion-panel-header>

        <mat-form-field>
            <input matInput placeholder="First name">
        </mat-form-field>

        <mat-form-field>
            <input matInput type="number" min="1" placeholder="Age">
        </mat-form-field>

        <mat-action-row>
            <button mat-button color="primary" (click)="nextStep()">Next</button>
        </mat-action-row>
    </mat-expansion-panel>

    <mat-expansion-panel [expanded]="step === 1" (opened)="setStep(1)" hideToggle="true">
        <mat-expansion-panel-header>
            <mat-panel-title>
                Destination
            </mat-panel-title>
            <mat-panel-description>
                Type the country name
                <mat-icon>map</mat-icon>
            </mat-panel-description>
        </mat-expansion-panel-header>

        <mat-form-field>
            <input matInput placeholder="Country">
        </mat-form-field>

        <mat-action-row>
            <button mat-button color="warn" (click)="prevStep()">Previous</button>
            <button mat-button color="primary" (click)="nextStep()">Next</button>
        </mat-action-row>
    </mat-expansion-panel>

    <mat-expansion-panel [expanded]="step === 2" (opened)="setStep(2)" hideToggle="true">
        <mat-expansion-panel-header>
            <mat-panel-title>
                Day of the trip
            </mat-panel-title>
            <mat-panel-description>
                Inform the date you wish to travel
                <mat-icon>date_range</mat-icon>
            </mat-panel-description>
        </mat-expansion-panel-header>

        <mat-form-field>
            <input matInput placeholder="Date" [matDatepicker]="picker" (focus)="picker.open()" readonly>
        </mat-form-field>
        <mat-datepicker #picker></mat-datepicker>

        <mat-action-row>
            <button mat-button color="warn" (click)="prevStep()">Previous</button>
            <button mat-button color="primary" (click)="nextStep()">End</button>
        </mat-action-row>
    </mat-expansion-panel>

</mat-accordion>

Answer 2

Simple implementation for array of panels

<mat-expansion-panel [expanded]="indexExpanded == i" disabled="true" *ngFor="...; let i = index">
    ...
    <button (click)="togglePanels(i)">Toggle</button>
    ...
</mat-expansion-panel>

And in code

indexExpanded: number = -1;

togglePanels(index: number) {
    this.indexExpanded = index == this.indexExpanded ? -1 : index;
}

Answer 3

Another very simple way to handle Mat Expansion panel programmatically is by using local references in Angular

<mat-accordion>
    <mat-expansion-panel #mep="matExpansionPanel">
    </mat-expansion-panel>
</mat-accordion>

Now in HTML(not accessible directly in TS file until we use @ViewChild) file use mep to expand or collapse Expansion panel using something like this:

<button (click)="mep.expanded = true;">Expand</button>
<button (click)="mep.expanded = false;">Collapse</button>