How to Upload File from Angular to ASP.NET Core Web API
Solution 1
my BlogController looks like this:
[HttpPost] public async Task<ActionResult<Blog>> PostBlog([FromForm]PostBlogModel blogModel)
It seems that you'd like to pass data using form-data, to achieve it, you can refer to the following code sample.
.component.html
<form [formGroup]="newBlogForm" (ngSubmit)="onSubmit(newBlogForm.value)">
<div>
<label for="Name">
Blog Name
</label>
<input type="text" formControlName="Name">
</div>
<div>
<label for="TileImage">
Tile Image
</label>
<input type="file" formControlName="TileImage" (change)="onSelectFile($event)" >
</div>
<button type="submit">Create Blog</button>
</form>
.component.ts
selectedFile: File = null;
private newBlogForm: FormGroup;
constructor(private http: HttpClient) { }
ngOnInit() {
this.newBlogForm = new FormGroup({
Name: new FormControl(null),
TileImage: new FormControl(null)
});
}
onSelectFile(fileInput: any) {
this.selectedFile = <File>fileInput.target.files[0];
}
onSubmit(data) {
const formData = new FormData();
formData.append('Name', data.Name);
formData.append('TileImage', this.selectedFile);
this.http.post('your_url_here', formData)
.subscribe(res => {
alert('Uploaded!!');
});
this.newBlogForm.reset();
}
Test Result
Solution 2
First
<input type="file">
binding with angular using ngModel
or formControlName
will only catch the value property
but actually when we submit form we need the files property
so we can create
custom directive that will apply to all the project <input type="file">
elements so when
we submit the form we got the file property
Before
import { Directive, forwardRef, HostListener, ElementRef, Renderer2 } from '@angular/core';
import { NG_VALUE_ACCESSOR, ControlValueAccessor } from '@angular/forms';
@Directive({
selector : `input[type=file][formControlName],
input[type=file][formControl],
input[type=file][ngModel]`,
providers: [
{
provide: NG_VALUE_ACCESSOR,
useExisting: FileValueAccessorDirective,
multi: true
}
]
})
export class FileValueAccessorDirective implements ControlValueAccessor {
constructor(private elementRef: ElementRef, private render: Renderer2) {
}
// Function to call when the file changes.
onChange = (file: any) => {}
//fire when the form value changed programmaticly
writeValue(value: any): void {
}
//fire only one time to register on change event
registerOnChange = (fn: any) => { this.onChange = fn; }
//fire only one time to register on touched event
registerOnTouched = (fn: any) => { }
//Disable the input
setDisabledState?(isDisabled: boolean): void {
}
//listen to change event
@HostListener('change', ['$event.target.files'])
handleChange(file) {
this.onChange(file[0]);
}
}
After
To upload file using Http your data shoud be encoded using multipart/form-data
that allows files to be send over http post so that why FormData
is used,
A FormData object will automatically generate request data with MIME type multipart/form-data that existing servers can process. To add a file field to the data you use a File object that an extension can construct from file path. The FormData object can then simply be passed to XMLHttpRequest:
so your submit method should be like
onSubmit() {
let formData: FormData = new FormData();
Object.keys(this.newBlogForm.value).forEach(key => {
formData.append(key, this.newBlogForm.value[key])
});
//pass formData to your service
}
Thrid
In your postBlog
method you are creating Subject
without any benefit , you can just return http.post then in the caller method use specifiy whether you subscribe
or use async/await
to make the http call fire
onSubmit() {
.....
this.postBlog(formData).subscribe(
result => { }
);
}
async onSubmit() {
.....
let res = await this.postBlog(formData).toPromise();
}
Robin Zimmerman
Updated on June 14, 2022Comments
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Robin Zimmerman almost 2 years
Similar questions have been asked but after looking through all of those and many blog posts on the subject I have not been able to figure this out so please forgive me.
I am creating a simple blog with (for the purposes of this question) two parts, a front end SPA in Angular 8 and a back-end API in ASP.NET Core 3. In one part of my front end I am attempting to upload an image to be used as the image for a newly created blog. When I try to upload an image, the resulting IFormFile in the backend is always coming out to
null
. Below is the code, any help is greatly appreciated!new-blog.component.html:
<form [formGroup]="newBlogForm" (ngSubmit)="onSubmit(newBlogForm.value)"> <div> <label for="Name"> Blog Name </label> <input type="text" formControlName="Name"> </div> <div> <label for="TileImage"> Tile Image </label> <input type="file" formControlName="TileImage"> </div> <button type="submit">Create Blog</button> </form>
new-blog.component.ts:
import { Component, OnInit } from '@angular/core'; import { FormBuilder, FormGroup, FormControl } from '@angular/forms'; import { BlogService } from '../blog-services/blog.service'; @Component({ selector: 'app-new-blog', templateUrl: './new-blog.component.html', styleUrls: ['./new-blog.component.css'] }) export class NewBlogComponent implements OnInit { private newBlogForm: FormGroup; constructor(private formBuilder: FormBuilder, private blogService: BlogService) { } ngOnInit() { this.newBlogForm = this.formBuilder.group({ Name: new FormControl(null), TileImage: new FormControl(null) }); } onSubmit(blogData: FormData) { console.log('new blog has been submitted.', blogData); this.blogService.postBlog(blogData); this.newBlogForm.reset(); } }
postBlog
from blog.service.ts:postBlog(blogData: FormData): Observable<any> { const postBlogSubject = new Subject(); this.appOptions.subscribe( (options) => { const url = options.blogAPIUrl + '/Blogs'; this.http .post(url, blogData) .subscribe( (blog) => { postBlogSubject.next(blog); } ); } ); return postBlogSubject.asObservable(); }
The signature for my BlogController looks like this:
[HttpPost] public async Task<ActionResult<Blog>> PostBlog([FromForm]PostBlogModel blogModel)
with the PostBlogModel as follows:
public class PostBlogModel { public string Name { get; set; } public IFormFile TileImage { get; set; } }
I have implemented logging middleware to try to debug. The output is as follows (I see that for some reason the front-end is sending application/json rather than multipart/form-data but I'm not sure why or how to fix...)
blogapi_1 | info: Microsoft.AspNetCore.Hosting.Diagnostics[2] blogapi_1 | Request finished in 170.16740000000001ms 500 blogapi_1 | info: Microsoft.AspNetCore.Hosting.Diagnostics[1] blogapi_1 | Request starting HTTP/1.1 OPTIONS http://localhost:5432/api/v1/Blogs blogapi_1 | dbug: BlogAPI.Middleware.RequestResponseLoggingMiddleware[0] blogapi_1 | HTTP Request: Headers: blogapi_1 | key: Connection, values: keep-alive blogapi_1 | key: Accept, values: */* blogapi_1 | key: Accept-Encoding, values: gzip, deflate, br blogapi_1 | key: Accept-Language, values: en-US,en-IN;q=0.9,en;q=0.8,en-GB;q=0.7 blogapi_1 | key: Host, values: localhost:5432 blogapi_1 | key: Referer, values: http://localhost:5431/blog/new-blog blogapi_1 | key: User-Agent, values: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/78.0.3904.108 Safari/537.36 blogapi_1 | key: Origin, values: http://localhost:5431 blogapi_1 | key: Access-Control-Request-Method, values: POST blogapi_1 | key: Access-Control-Request-Headers, values: content-type blogapi_1 | key: Sec-Fetch-Site, values: same-site blogapi_1 | key: Sec-Fetch-Mode, values: cors blogapi_1 | blogapi_1 | type: blogapi_1 | scheme: http blogapi_1 | host+path: localhost:5432/api/v1/Blogs blogapi_1 | queryString: blogapi_1 | body: blogapi_1 | info: Microsoft.AspNetCore.Cors.Infrastructure.CorsService[4] blogapi_1 | CORS policy execution successful. blogapi_1 | dbug: BlogAPI.Middleware.RequestResponseLoggingMiddleware[0] blogapi_1 | HTTP Response: Headers: blogapi_1 | key: Access-Control-Allow-Headers, values: Content-Type blogapi_1 | key: Access-Control-Allow-Origin, values: http://localhost:5431 blogapi_1 | blogapi_1 | statusCode: 204 blogapi_1 | responseBody: blogapi_1 | info: Microsoft.AspNetCore.Hosting.Diagnostics[2] blogapi_1 | Request finished in 58.5088ms 204 blogapi_1 | info: Microsoft.AspNetCore.Hosting.Diagnostics[1] blogapi_1 | Request starting HTTP/1.1 POST http://localhost:5432/api/v1/Blogs application/json 56 blogapi_1 | dbug: BlogAPI.Middleware.RequestResponseLoggingMiddleware[0] blogapi_1 | HTTP Request: Headers: blogapi_1 | key: Connection, values: keep-alive blogapi_1 | key: Content-Type, values: application/json blogapi_1 | key: Accept, values: application/json, text/plain, */* blogapi_1 | key: Accept-Encoding, values: gzip, deflate, br blogapi_1 | key: Accept-Language, values: en-US,en-IN;q=0.9,en;q=0.8,en-GB;q=0.7 blogapi_1 | key: Host, values: localhost:5432 blogapi_1 | key: Referer, values: http://localhost:5431/blog/new-blog blogapi_1 | key: User-Agent, values: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/78.0.3904.108 Safari/537.36 blogapi_1 | key: Origin, values: http://localhost:5431 blogapi_1 | key: Content-Length, values: 56 blogapi_1 | key: Sec-Fetch-Site, values: same-site blogapi_1 | key: Sec-Fetch-Mode, values: cors blogapi_1 | blogapi_1 | type: application/json blogapi_1 | scheme: http blogapi_1 | host+path: localhost:5432/api/v1/Blogs blogapi_1 | queryString: blogapi_1 | body: {"Name":"test","TileImage":"C:\\fakepath\\DSC_0327.jpg"}
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Silny ToJa over 3 yearsI am new in angular, can you explein me why dont it work without async Task<> in PostBlog and .subscribe(res => { alert('Uploaded!!');}); it dont throw exception but it does not enter to method.
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Wassim Katbey about 3 yearsDo you have to send the FormData object alone to the backend? I can't seem to wrap the FormData object in another object, and send that object altogether
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Faisal almost 3 yearswell explained.