ReactiveForm for dynamically updated form entries - html

Question

How to check status of myform in component to check if all the fields are filled or not?
HTML:
<div [formGroup]="myform">
<div *ngFor="let question of questions">
<label>{{question.question}}</label>
<select required >
<option selected disabled="disabled">Option</option>
<option *ngFor="let option of question['options']">{{option}}</option>
</select>
</div>
</div>
</div>
Question JSON coming from API:
this.questions = [
{
question: 'What is your age?',
options: ['20', '30', '40']
},
{
question: 'How much quantity?',
options: ['1','2','3']
}]

Answer 1

If you use ReactiveForm, you need use a FormArray
A FormArray can be of FormControl or a FormGroup
FormArray of FormControls
constructor(private fb:FormBuilder) {}
ngOnInit() {
//We create an array of FormControl, each question a FormControl
let data:FormControl[]=this.questions.map(q=>new FormControl());
this.myform=this.fb.group({
questions:new FormArray(data)
})
}
//the .html
<!--we use *ngIf to show the form only when we create the form-->
<div *ngIf="myform" [formGroup]="myform">
<!--we iterate to myForm.get('questions').controls -->
<!--we use our variable "questions" to show the label and options-->
<div *ngFor="let question of myform.get('questions').controls;let i=index">
<label>{{questions[i].question}}</label>
<select required [formControl]="question" >
<option value="null" disabled="disabled">Option</option>
<option *ngFor="let option of questions[i].options">{{option}}</option>
</select>
</div>
</div>
<!--just for check-->
{{myform?.value |json}}
If we use an array of formGroup we change some things
constructor(private fb:FormBuilder) {}
ngOnInit() {
//we create and array of FormGroup
let data2:FormGroup[]=this.questions.map(q=>this.fb.group({
option:null
}));
this.myform2=this.fb.group({
questions:new FormArray(data2)
})
}
<div *ngIf="myform2" [formGroup]="myform2">
<!--see that we say to Angular the "formArrayName" -->
<div formArrayName="questions">
<div *ngFor="let question of myform2.get('questions').controls;
let i=index" [formGroupName]="i"> <!--don't forget formGroupName-->
<label>{{questions[i].question}}</label>
<!--the select use formControlName, our array is an array of FormGroup-->
<select required formControlName="option" >
<option value="null" disabled="disabled">Option</option>
<option *ngFor="let option of questions[i].options">{{option}}</option>
</select>
</div>
</div>
</div>
{{myform2?.value |json}}
Aclaration:#FrontEndDeveloper. One thing is the array question that we use to make the questions.(Perhafs I must be choose other names to the variables), other thing is the value of the form. The value of myform1={questions:["20","1"]}, the value of myform2={questions:[{option:"20"},{option:"2"}]}.
When we create an array of FormControl (or an array of FbGroup) I used map, equally I can do some like
let data:FormControl[]=[];
data.push(new FormControl());
data.push(new FormControl());
or
let data2:FormGroup[]=[];
data2.push(this.fb.group({
option:null
}));
data2.push(this.fb.group({
option:null
}));
Generally we have some data to initialize the form. (an object with some data) that we get from a dbs
//Imagine we have mydata{name:"A",options=["20","1"]}
//we can map this data to create the form
let data:FormControl[]=this.mydata.options.map(q=>new FormControl(q));
//or
let data2:FormGroup[]=this.mydata.options.map(q=>this.fb.group({
option:q
}));
//Imagine we have mydata{name:"A",options=[{option:"20"},{option:"1"}]}
//we can map this data to create the form
let data:FormControl[]=this.mydata.options.map(q=>new FormControl(q.option));
//or
let data2:FormGroup[]=this.mydata.options.map(q=>this.fb.group({
option:q.option
}));

Answer 2

This would help you to understand reactive form basic functionalities.
https://stackblitz.com/edit/objects-equality-check-edhyk5?file=src/app/app.component.ts
It will help to understand:
1. FormBulder,
2. FormGroup,
3. Form Value changes etc.