Q:

Validating *ngFor used forms using angular 2 [formControl]

I have an angular Form and it used *ngFor for repeat an input box. Also, I have to validate dynamically all input boxes that are generated by *ngFor.
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
[{id:1,
mandatory:false,
questionDescription:"Blue flags are in position and contain words “Stop, Tank Car Connected” or “Stop, Men at Work”",
questionType:1,
validation:{maximum:100,minimum:0}},
{id:2,
mandatory:true,
questionDescription:"Wheels are chocked and handbrake(s) set” or “Stop, Men at Work",
questionType:2,
validation:{maxLength:10,minLength:3}}]

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

So in my case, all input boxes generate by *ngFor and I have to assign tags like firstName, lastName dynamically to those boxes.
So I used question.id 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>
                </ion-col>
              </ion-row>
            </div>

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

   </form>

The Problem is....
If I define [formControl] as [formControl]="inspectionForm.controls['{{question.id}}']"
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 [] and {{}} 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 
formControl="inspectionForm.controls['{{question.id}}']"

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
formControl="inspectionForm.controls['2']"

But the problem is if I define as follows with [formControl]
[formControl]="inspectionForm.controls['2']"

The app is Working Perfectly....
But I have to give question.id dynamically. How I can do that?
Are there someone have a solution for this error. Please give a suggestion.
Thank you very much.

A:

just use [formControl]="inspectionForm.controls[question.id]"
Thanks @Sasxa for the answer

