Dynamically Updating Radio Button Status in Angular 7 Using Material Design

I am currently working on an Angular Material application that includes radio buttons. My goal is to update the selected button based on data retrieved from a database. While everything seems to be functioning properly, I have noticed that the checked button only updates when there is an interaction with the page, such as a mouse click. Is it necessary for me to trigger change detection in this scenario?

HTML

<mat-radio-group name="animals" (change)="saveAnimal($event)">
   <mat-radio-button *ngFor="let option of animalOptions"
            [checked]="option.checked" value="{{option.value}}">{{option.label}}
  </mat-radio-button>
</mat-radio-group>

Component.ts

public animalOptions: any = [
      {label: 'cat', value: '1', checked: true},
      {label: 'dog', value: '2', checked: false}];

Subsequently, after retrieving the data from the API in the ngOnInit method:

if (this._choice.animal === 'cat') {
          this.animalOptions[0].checked = false;
          this.animalOptions[1].checked = true;
        }

Answer №1

Your implementation of dynamic rendering and manipulation of material radio button group values seems to be on point. However, the issue might stem from how or where the evaluation of this._choice.animal is taking place. If this value is obtained through a method like HttpClient get(), ensure that the evaluation of this._choice.animal occurs within the subscribe() or then() methods if it returns a Promise<T>:

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

@Component({
  selector: 'radio-overview-example',
  templateUrl: 'radio-overview-example.html',
  styleUrls: ['radio-overview-example.css'],
})
export class RadioOverviewExample {
  public animalOptions: any = [
    { label: 'cat', value: '1', checked: true },
    { label: 'dog', value: '2', checked: false }
  ];

  public _choice: any;

  ngOnInit() {
    this.getSomeApiValue().subscribe(result => {
      this._choice.animal = result;

      if (this._choice.animal === 'cat') {
        this.animalOptions[0].checked = false;
        this.animalOptions[1].checked = true;
      }
    });
  }
}

You can see this code in action with this live demo.

I hope this explanation clarifies things for you!

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