Update a formControl that is a file input in a formArray in Angular2

I also got this problem, but we can deal with file and other form field separately.

This is my code, I want to post a FormData Object to Django REST API, this formData contains both strings and image, also with user_name and password. I created a component - upload-image-form

This is what I want to post, an Image class(I define it by myself)

// images.ts
export class Image {

    constructor(
        public id: number,
        public created: string,  // set by back end
        public userId: number,
        public fileUrl: string,
        public owner: string,
        public des?: string,
        public localImage?: File,
    ) { }

}

This is my component

// upload-image-form.component.ts
import { Component, OnInit, Input } from '@angular/core';
import { NgForm } from '@angular/forms/forms';
import { FormControl, FormGroup, FormBuilder } from '@angular/forms';

import { Image } from '../image';
import { User } from '../user';
import { ImageService } from '../image.service';


@Component({
    selector: 'app-upload-image-form',
    templateUrl: './upload-image-form.component.html',
    styleUrls: ['./upload-image-form.component.css']
})
export class UploadImageFormComponent implements OnInit {

    @Input() user: User;  // this value comes from parent component user-detail's tempolate
    private file: File;
    private formData: FormData = new FormData();
    private imageForm: FormGroup;
    private submitted = false;
    private imageUrl = 'http://192.168.201.211:8024/images/';
    private password: string;

    constructor(
        private imageService: ImageService,
        private fb: FormBuilder,
    ) { }

    ngOnInit() {
        console.log(this.user);
        this.createFrom(this.user);  // create form here, so we can get this.user's value
    }

    createFrom(user: User) {
        // I didn't put file field in this form
        this.imageForm = this.fb.group({
            id: 1,
            created: '20170825',
            userId: user.id,
            fileUrl: 'http://images.fineartamerica.com/images-medium-large-5/mt-shuksan-picture-lake-dennis-romano.jpg',
            owner: user.username,
            des: '',
            pw: '',
        })
        console.log(user);
    }

    // https://stackoverflow.com/a/41465502/2803344
    // get a file object from form input
    onChange(event: EventTarget) {
        let eventObj: MSInputMethodContext = <MSInputMethodContext> event;
        let target: HTMLInputElement = <HTMLInputElement> eventObj.target;
        let files: FileList = target.files;
        this.file = files[0];
    }

    onSubmit() {
        // deal with string fields and file separately
        this.submitted = true;
        console.log(this.file);  // file is here, captured by onChange()
        console.log(this.imageForm.value);  // other fields are here, captured by formGroup

        this.formData.append('localImage', this.file, this.file.name);
        for (let item in this.imageForm.value) {
            console.log(item)
            if (item !== 'pw') {
                this.formData.append(item, this.imageForm.value[item]);
            }
            else {
                this.password = this.imageForm.value[item];
            }

        }

        // console.log('###here is the total form data');
        console.log(this.formData);
        console.log(this.formData.get('fileUrl'));
        console.log(this.user.username);
        this.imageService.post(this.formData, this.user.username, this.password)
                         .then(res =>{
                           console.log(res);
                         });
    }

    onClick(form: FormGroup) {
        form.reset({
            userId: this.user.id,
            owner: this.user.username,
            created: '20170825',
            fileUrl: 'http://www.fujifilm.com.sg/Products/digital_cameras/x/fujifilm_x_t1/sample_images/img/index/ff_x_t1_001.JPG',
        })
        this.submitted=false;
        console.log(form.value);
    }

}

This is my template

<!-- upload-image-form.component.html -->
<div [hidden]="submitted" *ngIf="user">

    <h2>Upload New Image</h2>

    <form [formGroup]="imageForm" (ngSubmit)="onSubmit()" >
        <div class="form-group">
            <label for="fileUrl">File Url</label>
            <input type="url" class="form-control" id="fileUrl" 
            formControlName="fileUrl" required>
            <div [hidden]="imageForm.get('fileUrl').valid || imageForm.get('fileUrl').pristine" 
                  class="alert alert-danger">
              File Url is required
            </div>
            <p>{{imageForm.get('fileUrl').valid | json}}</p>
            <p>{{imageForm.get('fileUrl').value | json}}</p>
        </div>
        <!-- upload an image 
        don't define this field in formGroup-->
        <div class="form-group">
            <label for="localImage">Local File</label>
            <input type="file" class="form-control" id="localImage"
            (change)="onChange($event)" accept=".jpg, .png" >
        </div>
        <div class="form-group">
            <label for="des">Description</label>
            <input type="text" class="form-control" id="des" 
            formControlName="des">
        </div>
        <div class="form-group">
            <label for="userId">User ID</label>
            <input type="text" class="form-control" id="userId" 
            formControlName="userId" readonly>
            <p>{{imageForm.get('userId').value | json}}</p>
        </div>
        <div class="form-group">
            <label for="owner">Owner</label>
            <input type="text" class="form-control" id="owner"
            formControlName="owner" readonly>
        </div>
        <!-- input user's password -->
        <div class="form-group">
            <label for="pw">password</label>
            <input type="password" class="form-control" id="pw"
            formControlName="pw" required>
        </div>
        <button type="submit" class="btn btn-success" [disabled]="!imageForm.valid">Submit</button>
    </form>
</div>

At last, this is my image service

// image.service.ts
import { Injectable } from '@angular/core';
import { Headers, Http, RequestOptions } from "@angular/http";

import 'rxjs/add/operator/toPromise';

import { Image } from "./image";
import { User } from './user';

@Injectable()
export class ImageService {

    private imageUrl = 'http://192.168.201.211:8024/images/';
    //set headers for authorization, https://stackoverflow.com/a/34465070/2803344
    createAuthorizationHeader(headers: Headers, name: string, pw: string) {
        headers.append('Authorization', 'Basic ' +
          btoa(`${name}:${pw}`)); 
    }

    createOptions(name: string, pw: string) {
        let headers = new Headers();
        this.createAuthorizationHeader(headers, name, pw);
        // headers.append('Content-Type', 'application/json');  // without this
        // headers.append('Content-Type', 'multipart/form-data');  // without this
        let options = new RequestOptions({ headers: headers });
        return options;
    }

    constructor(private http: Http) { }

    getImageById(id: number): Promise<Image> {
        const url = `${this.imageUrl}`;
        console.log(url);
        let headers = new Headers();
        let token = 'token';
        headers.append('X-Auth-Token', token);
        return this.http.get(url, {headers: headers})
                        .toPromise()
                        // .then(res => res.json().data as Image)
                        .then(res => console.log(res))
                        .catch(this.handleError);
    }

    getImageByUrl(url: string): Promise<Image> {
        return this.http.get(url)
                      .toPromise()
                      .then(res => res.json() as Image)
                      // .then(res => console.log(res))
                      .catch(this.handleError);
    }

    post(formData: FormData, user: string, pw: string): Promise<Image> {
        let options = this.createOptions(user, pw);
        console.log('we will have a post!');
        console.log(formData.get('localImage'));
        console.log(formData.get('fileUrl'));
        console.log(formData.get('des'));
        return this.http.post(this.imageUrl, formData, options)
                        .toPromise()
                        .then(res => res.json() as Image)
                        .catch(this.handleError);
    }

    private handleError(error: any): Promise<any> {
        console.error('An error occurred', error); // for demo purposes only
        return Promise.reject(error.message || error);
    }
}

You can find the whole project in github, https://github.com/OnlyBelter/image-sharing-system2.