write-value-2.ts

@Component({
  selector: 'app-root',
  template: `
    <multi-check-field [formControl]="multiCheckControl">
      <simple-check-option *ngFor="let subject of subjects"
        [value]="subject" [label]="subject.label">
      </simple-check-option>
    </multi-check-field>
    <button (click)="setTestValue()">Set Test Value</button>
    Control value: <pre>{{ multiCheckControl.value | json }}</pre>
  `,
})
export class AppComponent {

  public subjects = [
    { code: '001', label: 'Math' },
    { code: '002', label: 'Science' },
    { code: '003', label: 'History' },
  ];

  public multiCheckControl = new FormControl();

  setTestValue() {
    const testValue = [this.subjects[0], this.subjects[1]];
    this.multiCheckControl.setValue(testValue);
  }

}