Remove all items from a FormArray in Angular

I have a form array inside a FormBuilder and I am dynamically changing forms, i.e. on click load data from application 1 etc.

The issue I am having is that all the data loads in but the data in the FormArray stays and just concats the old items with new.

How do I clear that FormArray to only have the new items.

I've tried this

const control2 = <FormArray>this.registerForm.controls['other_Partners'];
control2.setValue([]);

but it doesn't work.

Any ideas?

ngOnInit(): void {
  this.route.params.subscribe(params => {
    if (params['id']) {
      this.id = Number.parseInt(params['id']);
    } else { this.id = null;}
  });
  if (this.id != null && this.id != NaN) {
    alert(this.id);
    this.editApplication();
    this.getApplication(this.id);
  } else {
    this.newApplication();
  }
}

onSelect(Editedapplication: Application) {
  this.router.navigate(['/apply', Editedapplication.id]);
}

editApplication() {
  this.registerForm = this.formBuilder.group({
    id: null,
    type_of_proposal: ['', Validators.required],
    title: ['', [Validators.required, Validators.minLength(5)]],
    lead_teaching_fellow: ['', [Validators.required, Validators.minLength(5)]],
    description: ['', [Validators.required, Validators.minLength(5)]],
    status: '',
    userID: JSON.parse(localStorage.getItem('currentUser')).username,
    contactEmail: JSON.parse(localStorage.getItem('currentUser')).email,
    forename: JSON.parse(localStorage.getItem('currentUser')).firstname,
    surname: JSON.parse(localStorage.getItem('currentUser')).surname,
    line_manager_discussion: true,
    document_url: '',
    keywords: ['', [Validators.required, Validators.minLength(5)]],
    financial_Details: this.formBuilder.group({
      id: null,
      buying_expertise_description: ['', [Validators.required, Validators.minLength(2)]],
      buying_expertise_cost: ['', [Validators.required]],
      buying_out_teaching_fellow_cost: ['', [Validators.required]],
      buying_out_teaching_fellow_desc: ['', [Validators.required, Validators.minLength(2)]],
      travel_desc: ['', [Validators.required, Validators.minLength(2)]],
      travel_cost: ['', [Validators.required]],
      conference_details_desc: ['', [Validators.required, Validators.minLength(2)]],
      conference_details_cost: ['', [Validators.required]],
    }),

    partners: this.formBuilder.array([
        //this.initEditPartner(),
        //this.initEditPartner()
        // this.initMultiplePartners(1)
      ]
    ),
    other_Partners: this.formBuilder.array([
      //this.initEditOther_Partners(),
    ])
  });
}

getApplication(id) {
  this.applicationService.getAppById(id, JSON.parse(localStorage.getItem('currentUser')).username)
    .subscribe(Response => {
      if (Response.json() == false) {
        this.router.navigateByUrl('/');
      } else {
        this.application = Response.json();
        for (var i = 0; i < this.application.partners.length;i++) {
          this.addPartner();
        }
        for (var i = 0; i < this.application.other_Partners.length; i++) {
          this.addOther_Partner();
        }

        this.getDisabledStatus(Response.json().status);
        (<FormGroup>this.registerForm) .setValue(Response.json(), { onlySelf: true });
      }
    });
}

ngOnInit is not being called on click

Solution 1:

I had same problem. There are two ways to solve this issue.

Preserve subscription

You can manually clear each FormArray element by calling the removeAt(i) function in a loop.

clearFormArray = (formArray: FormArray) => {
  while (formArray.length !== 0) {
    formArray.removeAt(0)
  }
}

The advantage to this approach is that any subscriptions on your formArray, such as that registered with formArray.valueChanges, will not be lost.

See the FormArray documentation for more information.

Cleaner method (but breaks subscription references)

You can replace whole FormArray with a new one.

clearFormArray = (formArray: FormArray) => {
  formArray = this.formBuilder.array([]);
}

This approach causes an issue if you're subscribed to the formArray.valueChanges observable! If you replace the FromArray with a new array, you will lose the reference to the observable that you're subscribed to.

Solution 2:

Or you can simply clear the controls

this.myForm= {
     name: new FormControl(""),
     desc: new FormControl(""),
     arr: new FormArray([])
}

Add something array

const arr = <FormArray>this.myForm.controls.arr;
arr.push(new FormControl("X"));

Clear the array

const arr = <FormArray>this.myForm.controls.arr;
arr.controls = [];

When you have multiple choices selected and clear, sometimes it doesn't update the view. A workaround is to add

arr.removeAt(0)

UPDATE

A more elegant solution to use form arrays is using a getter at the top of your class and then you can access it.

get inFormArray(): FormArray {
    this.myForm.get('inFormArray') as FormArray;
}

And to use it in a template

<div *ngFor="let c of inFormArray; let i = index;" [formGroup]="i">
other tags...
</div>

Reset:

inFormArray.reset();

Push:

inFormArray.push(new FormGroup({}));

Remove value at index: 1

inFormArray.removeAt(1);

UPDATE 2:

Get partial object, get all errors as JSON and many other features, use the NaoFormsModule

Solution 3:

As of Angular 8+ you can use clear() to remove all controls in the FormArray:

const arr = new FormArray([
   new FormControl(),
   new FormControl()
]);
console.log(arr.length);  // 2

arr.clear();
console.log(arr.length);  // 0

For previous versions the recommended way is:

while (arr.length) {
   arr.removeAt(0);
}

https://angular.io/api/forms/FormArray#clear

Solution 4:

Angular 8

simply use clear() method on formArrays :

(this.invoiceForm.controls['other_Partners'] as FormArray).clear();

Solution 5:

Warning!

The Angular v6.1.7 FormArray documentation says:

To change the controls in the array, use the push, insert, or removeAt methods in FormArray itself. These methods ensure the controls are properly tracked in the form's hierarchy. Do not modify the array of AbstractControls used to instantiate the FormArray directly, as that result in strange and unexpected behavior such as broken change detection.

Keep this in mind if you are using the splice function directly on the controls array as one of the answer suggested.

Use the removeAt function.

  while (formArray.length !== 0) {
    formArray.removeAt(0)
  }