如何将文件从 Angular 上传到 ASP.NET Core Web API

Question

有人提出了类似的问题，但在浏览了所有这些以及有关该主题的许多博客文章后，我无法弄清楚这一点，所以请原谅我。

我正在创建一个简单的博客，其中包含（出于此问题的目的）两部分，Angular 8 中的前端 SPA 和 ASP.NET Core 3 中的后端 API。在我前端的一部分中，我是尝试上传要用作新创建博客的图像的图像。当我尝试上传图片时，后端生成的 IFormFile 总是出现在null。以下是代码，非常感谢任何帮助！

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 来自 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();
  }

我的 BlogController 的签名如下所示：

[HttpPost]
public async Task<ActionResult<Blog>> PostBlog([FromForm]PostBlogModel blogModel)

使用 PostBlogModel 如下：

    public class PostBlogModel
    {
        public string Name { get; set; }
        public IFormFile TileImage { get; set; }
    }

我已经实现了日志中间件来尝试调试。输出如下（我看到由于某种原因前端正在发送 application/json 而不是 multipart/form-data 但我不确定为什么或如何修复......）

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"}

Answer 1

我的 BlogController 看起来像这样：

[HttpPost]

public async Task<ActionResult<Blog>> PostBlog([FromForm]PostBlogModel blogModel)

看来你想用form-data来传递数据，要实现，可以参考下面的代码示例。

.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();
}

测试结果

Answer 2

第一

<input type="file"> 使用ngModel 或formControlName 与角度绑定只会捕获value property 但实际上，当我们提交表单时，我们需要 files property 这样我们就可以创建 将适用于所有项目 <input type="file"> 元素的自定义指令，所以当 我们提交我们得到文件属性的表单

之前

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]);
    }

}

之后

第二

要使用 Http 上传文件，您的数据应该使用 multipart/form-data 编码，这允许文件通过 http post 发送，因此为什么使用 FormData，

FormData 对象将使用 MIME 自动生成请求数据 键入现有服务器可以处理的 multipart/form-data。添加一个 文件字段到您使用的数据的数据扩展可以使用的文件对象 从文件路径构造。然后 FormData 对象可以简单地是 传递给 XMLHttpRequest：

Http Upload Files

所以你的提交方法应该是这样的

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
  }

第三

在您的 postBlog 方法中，您正在创建 Subject 而没有任何好处，您可以只返回 http.post 然后在调用者方法中使用指定您是 subscribe 还是使用 async/await 来触发 http 调用

onSubmit() {
   .....
    this.postBlog(formData).subscribe(
        result => { }
    );
}

async onSubmit() {
   .....
    let res = await this.postBlog(formData).toPromise();
}