Angular reactive Form error: Must supply a value f

问题:

I premise I am very novice with angular. I am trying to implement an angular reactive form, but I am encountering this error: "Must supply a value for form control with name: Destination.

This is the relevant parts of my component and my html:

import { Component, Inject } from '@angular/core';
import { Http } from "@angular/http";
import { FormGroup, FormControl, FormBuilder, Validators } from "@angular/forms";

@Component({
    selector: 'home',
    templateUrl: './home.component.html'
})
export class HomeComponent {

    locations: Location[];
    flightChoice: FlightChoice;
    form: FormGroup;


    constructor(http: Http, @Inject('BASE_URL') private baseUrl: string,
        private fb: FormBuilder) {

        this.createForm();

        http.get(baseUrl + 'api/FlightChoice/dest_locations').subscribe(result => {
            this.locations = result.json() as Location[];
            console.log(this.locations);

        }, error => console.error(error));

        http.get(baseUrl + 'api/FlightChoice/choice').subscribe(result => {
            this.flightChoice = result.json() as FlightChoice;
            this.updateForm();
        }, error => console.error(error));

    }

    createForm() {
        this.form = this.fb.group({
            Destination: [0],
            NrPasg: [1],
            TwoWays: [false],
            DepartureDate: ['', Validators.required],
            ReturnDate: ['', Validators.required]
        });
    }

    updateForm() {

        this.form.setValue({
            Destination: this.flightChoice.DestinationId,
            NrPasg: this.flightChoice.NrPasg,
            TwoWays: this.flightChoice.TwoWays,
            DepartureDate: this.flightChoice.DepartureDate,
            ReturnDate: this.flightChoice.ReturnDate
        });

    }

html:

<form [formGroup]="form" (ngSubmit)="onSubmit()">
        <div>
            <label for="destination">Destination:</label>
            <br />
            <select id="destination" formControlName="Destination">
                <option *ngFor="let location of locations" value="{{ location.id }}">
                    {{ location.name }}
                </option>
            </select>
            <br />
            <label for="nrPasg">Number of Passengers:</label>
            <br />
            <input formControlName="NrPasg" type="number" id="nrPasg" value="1" />
            <label for="twoWays"></label>
            <br />
            <select id="twoWays" formControlName="TwoWays">
                <option value="false">one way</option>
                <option value="true">two ways</option>
            </select>
            <br />
            <label for="departureDate">Departure Date:</label>
            <br />
            <input formControlName="DepartureDate" type="date" id="departureDate" />
            <br />
            <label for="returnDate">Return Date:</label>
            <br />
            <input formControlName="ReturnDate" type="date" id="returnDate" />

        </div>
        <div>
            <button type="submit">Search Flights</button>

        </div>
    </form>

I know I am probably writing something wrong in the CreateForm method but I am not sure how to assign the values

回答1:

Probably the error appears because this.flightChoice.DestinationId === undefined and you try to set undefined to the Destination field on the form.

Check if api is correctly downloading data to this.flightChoice.

回答2:

This error can appear if you're using setValue on a formGroup but not passing in a value for every control within that group. For example:

let group = new FormGroup({
  foo: null, 
  bar: null
});
group.setValue({foo: 'only foo'}); //breaks
group.setValue({foo: 'foo', bar: 'bar'}); //works

If you truly want to only update some of the controls on the group, you can use patchValue instead:

group.patchValue({foo: 'only foo, no problem!'});

Docs for setValue and patchValue here

回答3:

Unfortunately 'undefined' isn't allowed, you need to set each property to 'null'.

It's perfectly legitimate to have a property set to undefined, common when coming directly from the server.

You can convert properties before calling setValue with something like this:

   // set all 'missing' OR 'undefined' properties to null
        const newValue: any = {...value};

        for (const field in this.controls) { 

            if (newValue[field] === undefined) {
                newValue[field] = null;
            }
        }

        super.setValue(newValue, options);

Watch out because JSON.stringify() will remove undefined, and so if you use that to send a value back to your server you need to make sure it can handle missing properties there.