[angular] How to set value to form control in Reactive Forms in Angular

Hi Everyone I'm new to angular. Actually, I'm trying to subscribe data from a service and that data, I'm passing to form control of mine from (example, it's like an edit form).

import { Component, OnInit } from '@angular/core';
import { FormBuilder, FormGroup, Validators, FormArray, FormControl } from '@angular/forms';
import { ActivatedRoute, Router } from '@angular/router';
import { QuestionService } from '../shared/question.service';

@Component({
  selector: 'app-update-que',
  templateUrl: './update-que.component.html',
  styleUrls: ['./update-que.component.scss']
})
export class UpdateQueComponent implements OnInit {

  questionsTypes = ['Text Type', 'Multiple choice', 'Single Select'];
  selectedQuestionType: string = "";
  question: any = {};

  constructor(private route: ActivatedRoute, private router: Router,
    private qService: QuestionService, private fb: FormBuilder) { 

  }

  ngOnInit() {
      this.getQuebyid();
  }

  getQuebyid(){
    this.route.params.subscribe(params => {
      this.qService.editQue([params['id']]).subscribe(res =>{
        this.question = res;
      });
    });
  }

  editqueForm =  this.fb.group({
    user: [''],
    questioning: ['', Validators.required],
    questionType: ['', Validators.required],
    options: new FormArray([])
  })

  setValue(){
    this.editqueForm.setValue({user: this.question.user, questioning: this.question.questioning})
  }

}

if I use [(ngModule)] on my form field to set the value to my element it is working fine and showing a warning it'll be deprecated in angular 7 version.

<textarea formControlName="questioning" [(ngModule)]="question.questioning" cols="70" rows="4"></textarea>

So, I set the values to my form control by doing below but the element is not showing those values.

setValue(){
   this.editqueForm.setValue({user: this.question.user, questioning: this.question.questioning})
}

can anyone tell me how to set values to mine reactive form. Please suggest me.

To assign value to a single Form control/individually, I propose to use setValue in the following way:

this.editqueForm.get('user').setValue(this.question.user);

this.editqueForm.get('questioning').setValue(this.question.questioning);

Use patchValue() method which helps to update even subset of controls.

setValue(){
  this.editqueForm.patchValue({user: this.question.user, questioning: this.question.questioning})
}

Error When strict checks fail, such as setting the value of a control that doesn't exist or if you excluding the value of a control.

In your case, object missing options and questionType control value so setValue() will fail to update.

The "usual" solution is make a function that return an empty formGroup or a fullfilled formGroup

createFormGroup(data:any)
{
 return this.fb.group({
   user: [data?data.user:null],
   questioning: [data?data.questioning:null, Validators.required],
   questionType: [data?data.questionType, Validators.required],
   options: new FormArray([this.createArray(data?data.options:null])
})
}

//return an array of formGroup
createArray(data:any[]|null):FormGroup[]
{
   return data.map(x=>this.fb.group({
        ....
   })
}

then, in SUBSCRIBE, you call the function

this.qService.editQue([params["id"]]).subscribe(res => {
  this.editqueForm = this.createFormGroup(res);
});

be carefull!, your form must include an *ngIf to avoid initial error

<form *ngIf="editqueForm" [formGroup]="editqueForm">
   ....
</form>

In Reactive Form, there are 2 primary solutions to update value(s) of form field(s).

setValue:

• Initialize Model Structure in Constructor:

  this.newForm = this.formBuilder.group({  
     firstName: ['', [Validators.required, Validators.minLength(3), Validators.maxLength(8)]],
     lastName: ['', [Validators.required, Validators.minLength(3), Validators.maxLength(8)]]
  });
  

• If you want to update all fields of form:

  this.newForm.setValue({
     firstName: 'abc',
     lastName: 'def'
  });
  

• If you want to update specific field of form:

  this.newForm.controls.firstName.setValue('abc');
  

Note: It’s mandatory to provide complete model structure for all form field controls within the FormGroup. If you miss any property or subset collections, then it will throw an exception.

patchValue:

• If you want to update some/ specific fields of form:

  this.newForm.patchValue({
     firstName: 'abc'
  });
  

Note: It’s not mandatory to provide model structure for all/ any form field controls within the FormGroup. If you miss any property or subset collections, then it will not throw any exception.

Try this.

editqueForm =  this.fb.group({
   user: [this.question.user],
   questioning: [this.question.questioning, Validators.required],
   questionType: [this.question.questionType, Validators.required],
   options: new FormArray([])
})

setValue() and patchValue()

if you want to set the value of one control, this will not work, therefor you have to set the value of both controls:

formgroup.setValue({name: ‘abc’, age: ‘25’});

It is necessary to mention all the controls inside the method. If this is not done, it will throw an error.

On the other hand patchvalue() is a lot easier on that part, let’s say you only want to assign the name as a new value:

formgroup.patchValue({name:’abc’});