Dilanka Rathnayake Dilanka Rathnayake - 13 days ago 10
HTML Question

Validating *ngFor used forms using angular 2 [formControl]

I have an angular Form and it used

for repeat an input box. Also, I have to validate dynamically all input boxes that are generated by

There is a JSON array called list that contains Questions. and I have to generate input boxes for answers and they should be validated. Validation information also in the list.

This is an example of the list

questionDescription:"Blue flags are in position and contain words “Stop, Tank Car Connected” or “Stop, Men at Work”",
questionDescription:"Wheels are chocked and handbrake(s) set” or “Stop, Men at Work",

I tried to validate generated input boxes as described in here.
https://scotch.io/tutorials/angular-2-form-validation (see validation forms there).

So I have to give validation information for each input boxes like below.
(this example from given tutorial)

constructor(fb: FormBuilder){
this.complexForm = fb.group({
'firstName' : [null, Validators.required],
'lastName': [null, Validators.compose([Validators.required, Validators.minLength(5), Validators.maxLength(10)])]

this is the HTML for it.

<div class="form-group">
<label>First Name:</label>
<input class="form-control" type="text"[formControl]="complexForm.controls['firstName']">
<div class="form-group" >
<label>Last Name</label>
<input class="form-control" type="text" [formControl]="complexForm.controls['lastName']">

So in my case, all input boxes generate by
and I have to assign tags like
dynamically to those boxes.
So I used
as that tag and implemented control group as followed.

inspectionForm: FormGroup;

constructor(fb: FormBuilder) {

this.questionTemplate = templateService.getQuestionTemplate();

let objString: string = "{";

for (let item of this.questionTemplate.sectionList[0].questionList) {
if (item.questionType == 2) {
objString += '"' + item.id + '":null,';

objString = objString.slice(0, -1);
objString += '}';
let objJson = JSON.parse(objString);

for (let item of this.questionTemplate.sectionList[0].questionList) {
if (item.questionType == 2) {
objJson[item.id] = [null,Validators.compose([Validators.minLength(item.validation.minLength), Validators.maxLength(item.validation.maxLength)])];
this.inspectionForm = fb.group(objJson);

and here is my HTML code.

<form [formGroup]="inspectionForm" (ngSubmit)="submitForm(inspectionForm.value)">

<div *ngFor="let question of section.questionList" [ngSwitch]="question.questionType">
<ion-row *ngSwitchCase="QuestionType.String">
<ion-col width-80>{{question.questionDescription}}</ion-col>
<ion-col width-20>
<ion-input id="{{question.id}}" type="text" class="inspection-bottom-border" [formControl]="inspectionForm.controls['{{question.id}}']"></ion-input>

<div class="form-group">
<button type="submit" class="btn btn-primary" [disabled]="!inspectionForm.valid">Submit</button>


The Problem is....

If I define

I get an error like follows,

unhandled Promise rejection: Template parse errors:
Parser Error: Got interpolation ({{}}) where expression was expected at column 25 in [inspectionForm.controls['{{question.id}}']] in InspectionPage@36:91 ("idth-20>
<ion-input id="{{question.id}}" type="text" class="inspection-bottom-border" [ERROR ->][formControl]="inspectionForm.controls['{{question.id}}']"></ion-input>

then I searched for an answer in StackOverflow, I found someone has said don't use
in one time (Dynamic routerLink value from ngFor item giving error "Got interpolation ({{}}) where expression was expected")

But if I removed
and defined as follows


I get an error as follows

EXCEPTION: Error in ./InspectionPage class InspectionPage - inline template:36:91 caused by: Cannot create property 'validator' on string 'inspectionForm.controls['2']'

(this '2' the is question.id of first type 2 question)

if I define as follows same error occurs


But the problem is if I define as follows with


The app is Working Perfectly....

But I have to give
dynamically. How I can do that?

Are there someone have a solution for this error. Please give a suggestion.

Thank you very much.


just use [formControl]="inspectionForm.controls[question.id]"

Thanks @Sasxa for the answer