set ngModel value to null after changing selected option - angular-reactive-forms

Question

i have a form which contains a select option and a div section depends on the selected option. in the select option if i choose 1 for exemple , an input will be displayed
component.ts
types : any[] = [
{ value : '1'},
{ value : '2'},
{ value : '3'}
];
createForm = this.fb.group({
firstInput:['',Validators.required],
secondInput:['',Validators.required],
thirdInput:['',Validators.required],
});
component.html
<select class="form-control" [value]="selected"[(ngModel)]="selectedValue">
<option *ngFor="let x of types">{{x.value}}</option>
</select>
<div *ngIf="selectedValue == '1'">
<label for="1" class="control-label">1</label>
<input id="1" class="form-control" type="text" formControlName="firstInput">
</div>
<div *ngIf="selectedValue == '2'">
<label for="2" class="control-label">2</label>
<input id="2" class="form-control" type="text" formControlName="secondInput">
</div>
<div *ngIf="selectedValue == '3'">
<label for="3" class="control-label">3</label>
<input id="3" class="form-control" type="text" formControlName="thirdInput">
</div>
all the fields are required, my problem is : when i choose "1" for exemple without filling the input of "1" then i change for the second choice "2" and fill it, i can't submit the form because the fielControllName "firstInput" is empty despite being invisible, so i need to clear the selected value of ngModel ( as i think ) with each change.

Answer 1

So Initially your form must be like:
createForm = this.fb.group({
selectedValue:[null,Validators.required],
firstInput:[null],
secondInput:[null],
thirdInput:[null],
});
Your HTML code:
<form [formGroup]="createForm">
<select class="form-control" formControlName="selectedValue">
<option *ngFor="let x of types" value="{{x.value}}">{{x.value}}</option>
</select>
<div *ngIf="createForm.value.selectedValue== '1'">
<label for="1" class="control-label">1</label>
<input id="1" class="form-control" type="text" formControlName="firstInput">
</div>
<div *ngIf="createForm.value.selectedValue== '2'">
<label for="2" class="control-label">2</label>
<input id="2" class="form-control" type="text" formControlName="secondInput">
</div>
<div *ngIf="createForm.value.selectedValue== '3'">
<label for="3" class="control-label">3</label>
<input id="3" class="form-control" type="text" formControlName="thirdInput">
</div>
</form>
Then you must have on change Function:
OnChange() {
this.createForm.get('selectedValue').valueChanges.subscribe(
val => {
if (val==1) {
this.createForm.get('firstInput').setValidators([Validators.required]);
this.createForm.controls['firstInput'].updateValueAndValidity();
this.createForm.get('secondInput').setValidators([]);
this.createForm.controls['secondInput'].updateValueAndValidity();
this.createForm.get('thirdInput').setValidators([]);
this.createForm.controls['thirdInput'].updateValueAndValidity();
}
else if (val==2) {
this.createForm.get('firstInput').setValidators([]);
this.createForm.controls['firstInput'].updateValueAndValidity();
this.createForm.get('secondInput').setValidators([Validators.required]);
this.createForm.controls['secondInput'].updateValueAndValidity();
this.createForm.get('thirdInput').setValidators([]);
this.createForm.controls['thirdInput'].updateValueAndValidity();
}
else if (val==3) {
this.createForm.get('firstInput').setValidators([]);
this.createForm.controls['firstInput'].updateValueAndValidity();
this.createForm.get('secondInput').setValidators([]);
this.createForm.controls['secondInput'].updateValueAndValidity();
this.createForm.get('thirdInput').setValidators([Validators.required]);
this.createForm.controls['thirdInput'].updateValueAndValidity();
}
}
)
}
if you want to make value null you can use:
this.createForm.patchValue({
firstInput:null,
secondInput:null,
thirdInput:null,
})