Angular How to patch value in the form array

Question

I am using Angular8 and reactive forms. My ngOnInit is:

ngOnInit(): void {
  this.makeForm = this.fb.group(
    year: ['', Validators.required],
    amount: ['', Validators.required],
    desc: ['', Validators.required],
    details: new FormArray([
      this.det(),
    ]
  );
}

det() {
  return new FormGroup({
    for: new FormControl(''),
    remarks: new FormControl('')
  });
}

I have the data from the backend to patch the array:

 {
  "amount": 9000,
  "year": 1996,
  "id": 1,
  "desc": "P1",
  "details": [
    {
      "id": 1,
      "remarks": "ok",
      "for": "1"
    },
    {
      "id": 24,
      "remarks": "OK",
      "for": "1"
    },
    {
      "id": 25,
      "remarks": "OK",
      "for": "1"
    }
  ]
 }

I commonly patch the values with this method:

getppredit() {
  let data:any = this.shareService.ParentShare.value;
  let id = data.id;
  this.dataService.getdataEdit(id)
    .subscribe((result: any) => {
      let no = result.no;
      let year = result.year;
      this.makeForm.patchValue({
        no: no,
        year: year
      });
  });
}

The above code is used for normal patch, but how to patch the value inside of an array dynamically using Angular8's reactive forms?

user_7237884 · Answer

Try this one here

    getppredit(){
      let data:any = this.shareService.ParentShare.value
      let id = data.id 
      this.dataService.getdataEdit(id)
        .subscribe((result: any)  => {
          let no = result.no;
          let year= result.year
          this.makeForm.patchValue({
              no     : no,
              year: year
              })

          //initialize empty array
          this.getFormArray() = new FormArray([]);

          //create needed formGroups and inside each formGroup all formControls
          for (let detail of result.details) {
            
            let idControl: FormControl = new FormControl('');
            let requestForControl: FormControl = new FormControl('');
            let remarkControl: FormControl = new FormControl('');

            idControl.setValue(detail.id);
            ForControl.setValue(detail.requestFor);
            remarkControl.setValue(detail.remark);

            this.getFormArray().push(new FormGroup({
              id: idControl,
              For: requestForControl,
              remark: remarkControl}));
           }

        })//end of subscribe
     
     }
    
        getFormArray(): FormArray{
            return this.makeForm.get('details') as FormArray;
          }

Form Arrays are usually intended to have dynamic data. Therefore you must first create your dynamic form controls inside the form array (after you have received your response) and then put values inside.

user_9878332 · Answer

here's how i would do it using FormArray, which tracks the value and validity state of an array of FormControl, FormGroup or FormArray instances:

export class Component implements OnInit {

  // initialize the FormArray with an empty array!
  formArray: FormArray = new FormArray([]);
  makeForm: FormGroup;

  ngOnInit() {
    this.makeForm = this.fb.group({
      no: ['', Validators.required],
      year: ['', Validators.required],
    });
  }

  getParEdit() {
    ...
    this.dataService.getDataEdit(id).subscribe(result => {
      const { no, year, details } = result;
      this.makeForm.patchValue({ no, year });

      if (details.length) {
        details.forEach(detail => {
          this.formArray.push(
            this.fb.group({
              id: new FormControl({ value: detail.id }),
              requestFor: new FormControl({ value: detail.requestFor }),
              remark: new FormControl({ value: detail.remark }),
            });
          );
        });
      }
    });
  }
}

you can dynamically create the FormGroup for each detail iteration, as well as the FormControls in each.

Angular How to patch value in the form array

2 Answers