typescript - Angular 4: bajo el método ngOnInit(), no se puede obtener el valor del elemento del formulario. Aparece el error 'get' is undefined

Descripción:

Angular 4, enfoque reactivo, intentando comparar los valores de los campos creando una función validadora y pasando esa función dentro del método ngOnInit().

Por favor, encuentra mi código a continuación,

import { Component, OnInit } from '@angular/core';
import {BsModalRef} from "ngx-bootstrap";
import {FormGroup, FormControl, Validators} from "@angular/forms";

@Component({
  selector: 'app-formcontent',
  templateUrl: './formcontent.component.html',
  styleUrls: ['./formcontent.component.css']
})

export class FormcontentComponent implements OnInit {

  signupForm: FormGroup;
  constructor(public bsModalRef: BsModalRef) { }

ngOnInit() {
    this.signupForm = new FormGroup({
      'firstname': new FormControl(null, Validators.required),
      'lastname': new FormControl(null, Validators.required),
      'email': new FormControl(null, [Validators.required, Validators.email]),
      'password': new FormControl(null, Validators.required),
      'cnfpwd': new FormControl(null, [Validators.required, this.checkPassword.bind(this)]),
     'checkb': new FormControl('checked', Validators.required)
    });
  }

 checkPassword(control: FormControl): {[s: string]: boolean} {
    if(control.value === this.signupForm.get('password').value){
      return {'isConfirmPasswordValid': true}
    }
    return null;
  }

  onSubmit(){
    console.log(this.signupForm.value.firstname);
    console.log(this.signupForm.valid);
  }

}

En el código anterior he creado la función validadora 'checkPassword' para comparar el valor del control con el valor de la contraseña. Cuando paso esta función bajo el método ngOnInit() como parte de la función validadora al campo 'cnfpwd', en tiempo de ejecución, estoy obteniendo el siguiente error.

FormcontentComponent_Host.html:1 ERROR TypeError: Cannot read property 'get' of undefined
    at FormcontentComponent.webpackJsonp.../../../../../src/app/formcontent/formcontent.component.ts.FormcontentComponent.checkPassword (formcontent.component.ts:28)
    at forms.es5.js:443
    at Array.map (<anonymous>)
    at _executeValidators (forms.es5.js:443)
    at FormControl.validator (forms.es5.js:399)
    at FormControl.webpackJsonp.../../../forms/@angular/forms.es5.js.AbstractControl._runValidator (forms.es5.js:2645)
    at FormControl.webpackJsonp.../../../forms/@angular/forms.es5.js.AbstractControl.updateValueAndValidity (forms.es5.js:2613)
    at new FormControl (forms.es5.js:2936)
    at FormcontentComponent.webpackJsonp.../../../../../src/app/formcontent/formcontent.component.ts.FormcontentComponent.ngOnInit (formcontent.component.ts:22)
    at checkAndUpdateDirectiveInline (core.es5.js:10836)
View_FormcontentComponent_Host_0 @ FormcontentComponent_Host.html:1
proxyClass @ compiler.es5.js:14971
webpackJsonp.../../../core/@angular/core.es5.js.DebugContext_.logError @ core.es5.js:13398
webpackJsonp.../../../core/@angular/core.es5.js.ErrorHandler.handleError @ core.es5.js:1080
(anonymous) @ core.es5.js:9216
(anonymous) @ platform-browser.es5.js:2651
webpackJsonp.../../../../zone.js/dist/zone.js.ZoneDelegate.invokeTask @ zone.js:424
onInvokeTask @ core.es5.js:3881
webpackJsonp.../../../../zone.js/dist/zone.js.ZoneDelegate.invokeTask @ zone.js:423
webpackJsonp.../../../../zone.js/dist/zone.js.Zone.runTask @ zone.js:191
webpackJsonp.../../../../zone.js/dist/zone.js.ZoneTask.invokeTask @ zone.js:498
invokeTask @ zone.js:1370
globalZoneAwareCallback @ zone.js:1388
FormcontentComponent_Host.html:1 ERROR CONTEXT DebugContext_ {view: {…}, nodeIndex: 0, nodeDef: {…}, elDef: {…}, elView: {…}}
View_FormcontentComponent_Host_0 @ FormcontentComponent_Host.html:1
proxyClass @ compiler.es5.js:14971
webpackJsonp.../../../core/@angular/core.es5.js.DebugContext_.logError @ core.es5.js:13398
webpackJsonp.../../../core/@angular/core.es5.js.ErrorHandler.handleError @ core.es5.js:1085
(anonymous) @ core.es5.js:9216
(anonymous) @ platform-browser.es5.js:2651
webpackJsonp.../../../../zone.js/dist/zone.js.ZoneDelegate.invokeTask @ zone.js:424
onInvokeTask @ core.es5.js:3881
webpackJsonp.../../../../zone.js/dist/zone.js.ZoneDelegate.invokeTask @ zone.js:423
webpackJsonp.../../../../zone.js/dist/zone.js.Zone.runTask @ zone.js:191
webpackJsonp.../../../../zone.js/dist/zone.js.ZoneTask.invokeTask @ zone.js:498
invokeTask @ zone.js:1370
globalZoneAwareCallback @ zone.js:1388
FormcontentComponent.html:2 ERROR Error: formGroup expects a FormGroup instance. Please pass one in.

       Example:


    <div [formGroup]="myGroup">
      <input formControlName="firstName">
    </div>

    In your class:

    this.myGroup = new FormGroup({
       firstName: new FormControl()
    });
    at Function.webpackJsonp.../../../forms/@angular/forms.es5.js.ReactiveErrors.missingFormException (forms.es5.js:4437)
    at FormGroupDirective.webpackJsonp.../../../forms/@angular/forms.es5.js.FormGroupDirective._checkFormPresent (forms.es5.js:4858)
    at FormGroupDirective.webpackJsonp.../../../forms/@angular/forms.es5.js.FormGroupDirective.ngOnChanges (forms.es5.js:4688)
    at checkAndUpdateDirectiveInline (core.es5.js:10833)
    at checkAndUpdateNodeInline (core.es5.js:12332)
    at checkAndUpdateNode (core.es5.js:12271)
    at debugCheckAndUpdateNode (core.es5.js:13132)
    at debugCheckDirectivesFn (core.es5.js:13073)
    at Object.eval [as updateDirectives] (FormcontentComponent.html:2)
    at Object.debugUpdateDirectives [as updateDirectives] (core.es5.js:13058)
View_FormcontentComponent_0 @ FormcontentComponent.html:2
proxyClass @ compiler.es5.js:14971
webpackJsonp.../../../core/@angular/core.es5.js.DebugContext_.logError @ core.es5.js:13398
webpackJsonp.../../../core/@angular/core.es5.js.ErrorHandler.handleError @ core.es5.js:1080
(anonymous) @ core.es5.js:4814
webpackJsonp.../../../../zone.js/dist/zone.js.ZoneDelegate.invoke @ zone.js:391
webpackJsonp.../../../../zone.js/dist/zone.js.Zone.run @ zone.js:141
webpackJsonp.../../../core/@angular/core.es5.js.NgZone.runOutsideAngular @ core.es5.js:3844
webpackJsonp.../../../core/@angular/core.es5.js.ApplicationRef_.tick @ core.es5.js:4814
(anonymous) @ core.es5.js:4684
webpackJsonp.../../../../zone.js/dist/zone.js.ZoneDelegate.invoke @ zone.js:391
onInvoke @ core.es5.js:3890
webpackJsonp.../../../../zone.js/dist/zone.js.ZoneDelegate.invoke @ zone.js:390
webpackJsonp.../../../../zone.js/dist/zone.js.Zone.run @ zone.js:141
webpackJsonp.../../../core/@angular/core.es5.js.NgZone.run @ core.es5.js:3821
next @ core.es5.js:4684
schedulerFn @ core.es5.js:3635
webpackJsonp.../../../../rxjs/Subscriber.js.SafeSubscriber.__tryOrUnsub @ Subscriber.js:238
webpackJsonp.../../../../rxjs/Subscriber.js.SafeSubscriber.next @ Subscriber.js:185
webpackJsonp.../../../../rxjs/Subscriber.js.Subscriber._next @ Subscriber.js:125
webpackJsonp.../../../../rxjs/Subscriber.js.Subscriber.next @ Subscriber.js:89
webpackJsonp.../../../../rxjs/Subject.js.Subject.next @ Subject.js:55
webpackJsonp.../../../core/@angular/core.es5.js.EventEmitter.emit @ core.es5.js:3621
checkStable @ core.es5.js:3855
onLeave @ core.es5.js:3934
onInvokeTask @ core.es5.js:3884
webpackJsonp.../../../../zone.js/dist/zone.js.ZoneDelegate.invokeTask @ zone.js:423
webpackJsonp.../../../../zone.js/dist/zone.js.Zone.runTask @ zone.js:191
webpackJsonp.../../../../zone.js/dist/zone.js.ZoneTask.invokeTask @ zone.js:498
invokeTask @ zone.js:1370
globalZoneAwareCallback @ zone.js:1388
FormcontentComponent.html:2 ERROR CONTEXT DebugContext_ {view: {…}, nodeIndex: 4, nodeDef: {…}, elDef: {…}, elView: {…}}

No se puede encontrar una solución, ¿podrías indicarme alguna solución? Gracias.

Respuesta #1

Deberías crear el formulario reactivo en el constructor del componente, no en ngOnInit. https://angular.io/guide/reactive-forms#introduction-to-formbuilder

Respuesta #2

Andre tiene razón. Estás examinando el FormGroup antes de que se instancie. Para corregir tu error, cambia la función checkPassword y cualquier otro validador para verificar si el FormGroup existe primero, antes de hacer el trabajo.

checkPassword(control: FormControl): {[s: string]: boolean} {
  if (!this.signupForm) {
    return null;
  }

  if(control.value === this.signupForm.get('password').value){
    return {'isConfirmPasswordValid': true}
  }
  return null;
}