Angular 2: formGroup expects a FormGroup instance. Please pass one in

问题:

I am creating a form in Angular 2. My goal is to get data from the API and pass it into the form for editing purposes. However, I am running into this error:

EXCEPTION: Uncaught (in promise): Error: Error in ./EditPatientComponent class EditPatientComponent - inline template:1:10 caused by: formGroup expects a FormGroup instance. Please pass one in.

Here is the current code with the error.

html

<section class="CreatePatient">     <form [formGroup]="patientForm" (ngSubmit)="onSubmit()">         <div class="row">             <div class="form-group col-12 col-lg-3">                 <label for="firstName">First Name</label>                 <input formControlName="firstName" type="text" class="form-control" id="firstName" >             </div>          <div class="row">             <div class="col-12 col-lg-2">                 <button type="submit" name="submit" class="btn btn-block btn-primary">Save</button>             </div>         </div>     </form> </section> 

ts

import { Component, OnInit } from '@angular/core'; import { ActivatedRoute, Router } from '@angular/router'; import { FormBuilder, FormGroup, FormControl } from '@angular/forms';  import { PatientService } from './patient.service'; import { Patient } from './patient';  @Component({     templateUrl: 'editpatient.component.html' }) export class EditPatientComponent implements OnInit {     errorMessage: string;     id: string;     editMode = true;     private patientForm: FormGroup;     private patient: Patient;      constructor(         private patientService: PatientService,         private router: Router,         private activatedRoute: ActivatedRoute,         private formBuilder: FormBuilder) {          console.log("routes");         console.log(activatedRoute.snapshot.url[1].path);     }      ngOnInit() {         this.getPatient();     }      getPatient() {             this.patientService.getPatient(this.activatedRoute.snapshot.url[1].path)             .subscribe(                 patient => {                     this.id = this.activatedRoute.snapshot.url[1].path;                     this.patient = patient;                     this.initForm();                 },                 error =>  this.errorMessage = <any>error);      }      onSubmit(form){         console.log(this.patientForm);         // Post the API     };      initForm() {         let patientFirstName = '';          if (this.editMode) {             console.log(this.patient.firstName);             console.log(this.patient.lastName);             console.log(this.patient.participantUuid);             patientFirstName = this.patient.firstName;         }          this.patientForm = new FormGroup({             'firstName': new FormControl(patientFirstName)         })     };  } 

Any help/pointing me in the right direction would be great! Thanks!

回答1:

Your patientForm is undefined until the patient in the subscription is populated. As such, you're trying to bind to a value that doesn't exist in the template at the time the template is parsed.

Add an *ngIf to render the form only when patient is truthy:

<section class="CreatePatient">     <form *ngIf="patient" [formGroup]="patientForm" (ngSubmit)="onSubmit()">         <div class="row">             <div class="form-group col-12 col-lg-3">                 <label for="firstName">First Name</label>                 <input formControlName="firstName" type="text" class="form-control" id="firstName" >             </div>          <div class="row">             <div class="col-12 col-lg-2">                 <button type="submit" name="submit" class="btn btn-block btn-primary">Save</button>             </div>         </div>     </form> </section> 

When the patient is populated in the subscription, the patientForm instance will exist and the binding will work. It's a common "gotcha" when dealing with async values.

回答2:

Problem is that your form is null on the beginning.

And only on ng init you will get patient and then create it. You should initialize your form on the begining or

<section class="CreatePatient" *ngIf="patientForm"> 

文章来源: Angular 2: formGroup expects a FormGroup instance. Please pass one in