forms - Angular 2 : formGroup expects a FormGroup instance. 请传入一个

Question

我正在 Angular 2 中创建一个表单。我的目标是从 API 获取数据并将其传递到表单中以进行编辑。但是，我遇到了这个错误:

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.

这是有错误的当前代码。

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)
        })
    };

}

任何帮助/指向正确方向的帮助都会很棒!谢谢!

Answer 1

您的 patientForm 是 undefined 直到订阅中的 patient 被填充。因此，您试图绑定(bind)到一个在解析模板时模板中不存在的值。

添加一个 *ngIf 以仅在 patient 为真或实例化表单组时呈现表单:

<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>

当订阅中填充患者时，patientForm 实例将存在并且绑定(bind)将起作用。在处理异步值时，这是一个常见的“陷阱”。

表单并不总是有起始值，因此您还可以检查表单本身是否存在:

<form *ngIf="patientForm" [formGroup]="patientForm" (ngSubmit)="onSubmit()">

重要的是表单在实例化之前不会呈现。