Reactive form using multiple selection on new option selection error

Question

Is there an example on how to implement multiple selection and reactive form ?

I'm trying to set the selected items (retrieved from the database) on the multiselect-dropdown, it will update the items displayed (the view), but it throws following error:

core.js:12501 ERROR TypeError: control.registerOnChange is not a function
    at setUpModelChangePipeline (forms.js:2064)
    at setUpControl (forms.js:2007)
    atFormGroupDirective.push../node_modules/@angular/forms/fesm5/forms.js.FormGroupDirective.addControl 
    (forms.js:4969)
    at FormControlName.push../node_modules/@angular/forms/fesm5/forms.js.FormControlName._setUpControl 
    (forms.js:5572)
    at FormControlName.push../node_modules/@angular/forms/fesm5/forms.js.FormControlName.ngOnChanges 
    (forms.js:5491)
    at checkAndUpdateDirectiveInline (core.js:18533)
    at checkAndUpdateNodeInline (core.js:19801)
    at checkAndUpdateNode (core.js:19763)
    at prodCheckAndUpdateNode (core.js:20304)
    at Object.eval [as updateDirectives] (AddAppointmentsComponent.ngfactory.js:646)

I was trying to select new option getting error.

core.js:12501 ERROR Error: Cannot find form control at index 3
    at FormArray.push../node_modules/@angular/forms/fesm5/forms.js.FormArray._throwIfControlMissing (forms.js:4001)
    at forms.js:3870
    at Array.forEach (<anonymous>)
    at FormArray.push../node_modules/@angular/forms/fesm5/forms.js.FormArray.setValue (forms.js:3869)
    at updateControl (forms.js:2059)
    at MultiSelectComponent.onChangeCallback (forms.js:2044)
    at MultiSelectComponent.push../node_modules/ng-multiselect-dropdown/fesm5/ng-multiselect- 
    dropdown.js.MultiSelectComponent.addSelected (ng-multiselect-dropdown.js:348)
    at MultiSelectComponent.push../node_modules/ng-multiselect-dropdown/fesm5/ng-multiselect- 
    dropdown.js.MultiSelectComponent.onItemClick (ng-multiselect-dropdown.js:160)
    at Object.eval [as handleEvent] (MultiSelectComponent.ngfactory.js:135)
    at Object.handleEvent (core.js:19545)

data

"questionnaireData":[{"questionnaireId":"Xvqo5atpw",

                      "timeRepeat":[    
                                    {"item_id":1,"item_text":"01:00"},
                                    {"item_id":2,"item_text":"02:00"},
                                    {"item_id":2,"item_text":"02:00"}
                                   ]    
                    }],

In the component formArray assigning to formBuilder.array(ap.timeRepeat).

component.ts

this.addAppointmentForm.setControl('questionnaireData', 
this.setExistingQuestionnairesDetails(this.AppointmentList.questionnaireData));

setExistingQuestionnairesDetails(questionDataArray: IQuestionnaireData[]): FormArray {
    const formArray = new FormArray([]);
    console.log(questionDataArray);
    questionDataArray.forEach(ap=>{

      formArray.push(this.formBuilder.group({
        questionnaireId: ap.questionnaireId,
        timeRepeat: this.formBuilder.array(ap.timeRepeat),

      }))
    })
    return formArray;
  }

compnent.html

<ng-multiselect-dropdown formControlName="timeRepeat" [data]="dropdownList"
  [(ngModel)]="timeRepeat" [settings]="dropdownSettings" (onSelect)="onItemSelect($event)" 
  (onSelectAll)="onSelectAll($event)" (onDeSelect)="onDeSelect($event)">
 </ng-multiselect-dropdown>

Please let me know how I can get around this error or some better way to get things done.

Answer 1

don't mix Reactive and template forms (not use for a controel [(ngModel)] and formControlName for the same input). And if you use a control, you needn't use (onDeSelect, onSelectAll nor onSelect). BTW, a ng-multiselect-dropdown store an array.

Yes, you needn't a FormArray, just a formControl (or if you use [(ngModel)] an unique variable that is an array). And yes, a FormControl can store an array or an object

The most simple example in stackblitz

We has a data

  this.data = [
      { item_id: 1, item_text: 'Hanoi' },
      { item_id: 2, item_text: 'Lang Son' },
      { item_id: 3, item_text: 'Vung Tau' },
      { item_id: 4, item_text: 'Hue' },
      { item_id: 5, item_text: 'Cu Chi' }
    ];

and the form is

   this.form = new FormGroup({
      name: new FormControl([this.data[0],this.data[2]], Validators.required)
    });

The .html

<form [formGroup]="form" (ngSubmit)="save()" (reset)="resetForm()">

    <ng-multiselect-dropdown #multiSelect
      [placeholder]="'Select City'" 
      [data]="data" 
      formControlName="name" 
      [settings]="settings"
      [disabled]="false"
>
        </ng-multiselect-dropdown>

    <span *ngIf="form.get('name')?.errors?.required" style="color: red;">
      City is required
    </span>

    <br/><br/>

    <input type="submit" value="Submit"> | <input type="reset" value="Reset">

  </form>