下面是一个上传文件到api的例子:

步骤1:HTML模板

定义文件类型的简单输入标记。为(change)-event添加一个处理选择文件的函数。

<div class="form-group">
    <label for="file">Choose File</label>
    <input type="file"
           id="file"
           (change)="handleFileInput($event.target.files)">
</div>

步骤2:在TypeScript中处理上传

为所选文件定义一个默认变量。

fileToUpload: File | null = null;

创建你在(change)-event中使用的函数:

handleFileInput(files: FileList) {
    this.fileToUpload = files.item(0);
}

如果你想处理多文件选择，那么你可以遍历这个文件数组。

现在通过调用file-upload.service创建文件上传函数:

uploadFileToActivity() {
    this.fileUploadService.postFile(this.fileToUpload).subscribe(data => {
      // do something, if upload success
      }, error => {
        console.log(error);
      });
  }

第三步:文件上传服务

通过post方法上传文件，你应该使用FormData，因为这样你可以添加文件到http请求。

postFile(fileToUpload: File): Observable<boolean> {
    const endpoint = 'your-destination-url';
    const formData: FormData = new FormData();
    formData.append('fileKey', fileToUpload, fileToUpload.name);
    return this.httpClient
      .post(endpoint, formData, { headers: yourHeadersConfig })
      .map(() => { return true; })
      .catch((e) => this.handleError(e));
}

所以，这是一个非常简单的工作例子，我每天都在工作中使用。

在我的情况下，我使用http拦截器，事情是，默认情况下，我的http拦截器设置内容类型头为应用程序/json，但对于文件上传，我使用multer库。 稍微改变一下我的http。interceptor定义，如果请求体是FormData，它会删除头，不触及访问令牌。 下面是一部分代码，它让我很开心。

if (request.body instanceof FormData) {
  request = request.clone({ headers: request.headers.delete('Content-Type', 'application/json') });
}

if (request.body instanceof FormData) {
  request = request.clone({ headers: request.headers.delete('Accept', 'application/json')});
}

下面是一个上传文件到api的例子:

步骤1:HTML模板

定义文件类型的简单输入标记。为(change)-event添加一个处理选择文件的函数。

<div class="form-group">
    <label for="file">Choose File</label>
    <input type="file"
           id="file"
           (change)="handleFileInput($event.target.files)">
</div>

步骤2:在TypeScript中处理上传

为所选文件定义一个默认变量。

fileToUpload: File | null = null;

创建你在(change)-event中使用的函数:

handleFileInput(files: FileList) {
    this.fileToUpload = files.item(0);
}

如果你想处理多文件选择，那么你可以遍历这个文件数组。

现在通过调用file-upload.service创建文件上传函数:

uploadFileToActivity() {
    this.fileUploadService.postFile(this.fileToUpload).subscribe(data => {
      // do something, if upload success
      }, error => {
        console.log(error);
      });
  }

第三步:文件上传服务

通过post方法上传文件，你应该使用FormData，因为这样你可以添加文件到http请求。

postFile(fileToUpload: File): Observable<boolean> {
    const endpoint = 'your-destination-url';
    const formData: FormData = new FormData();
    formData.append('fileKey', fileToUpload, fileToUpload.name);
    return this.httpClient
      .post(endpoint, formData, { headers: yourHeadersConfig })
      .map(() => { return true; })
      .catch((e) => this.handleError(e));
}

所以，这是一个非常简单的工作例子，我每天都在工作中使用。

在Angular 7/8/9中

来源链接

使用自举表单

<form>
    <div class="form-group">
        <fieldset class="form-group">

            <label>Upload Logo</label>
            {{imageError}}
            <div class="custom-file fileInputProfileWrap">
                <input type="file" (change)="fileChangeEvent($event)" class="fileInputProfile">
                <div class="img-space">

                    <ng-container *ngIf="isImageSaved; else elseTemplate">
                        <img [src]="cardImageBase64" />
                    </ng-container>
                    <ng-template #elseTemplate>

                        <img src="./../../assets/placeholder.png" class="img-responsive">
                    </ng-template>

                </div>

            </div>
        </fieldset>
    </div>
    <a class="btn btn-danger" (click)="removeImage()" *ngIf="isImageSaved">Remove</a>
</form>

在组件类中

fileChangeEvent(fileInput: any) {
    this.imageError = null;
    if (fileInput.target.files && fileInput.target.files[0]) {
        // Size Filter Bytes
        const max_size = 20971520;
        const allowed_types = ['image/png', 'image/jpeg'];
        const max_height = 15200;
        const max_width = 25600;

        if (fileInput.target.files[0].size > max_size) {
            this.imageError =
                'Maximum size allowed is ' + max_size / 1000 + 'Mb';

            return false;
        }

        if (!_.includes(allowed_types, fileInput.target.files[0].type)) {
            this.imageError = 'Only Images are allowed ( JPG | PNG )';
            return false;
        }
        const reader = new FileReader();
        reader.onload = (e: any) => {
            const image = new Image();
            image.src = e.target.result;
            image.onload = rs => {
                const img_height = rs.currentTarget['height'];
                const img_width = rs.currentTarget['width'];

                console.log(img_height, img_width);


                if (img_height > max_height && img_width > max_width) {
                    this.imageError =
                        'Maximum dimentions allowed ' +
                        max_height +
                        '*' +
                        max_width +
                        'px';
                    return false;
                } else {
                    const imgBase64Path = e.target.result;
                    this.cardImageBase64 = imgBase64Path;
                    this.isImageSaved = true;
                    // this.previewImagePath = imgBase64Path;
                }
            };
        };

        reader.readAsDataURL(fileInput.target.files[0]);
    }
}

removeImage() {
    this.cardImageBase64 = null;
    this.isImageSaved = false;
}

首先，你需要在你的Angular项目中设置HttpClient。

打开src/app/app.module。导入HttpClientModule并将其添加到模块的imports数组中，如下所示:

import { BrowserModule } from '@angular/platform-browser';  
import { NgModule } from '@angular/core';
import { AppRoutingModule } from './app-routing.module';  
import { AppComponent } from './app.component';  
import { HttpClientModule } from '@angular/common/http';

@NgModule({  
  declarations: [  
    AppComponent,  
  ],  
  imports: [  
    BrowserModule,  
    AppRoutingModule,  
    HttpClientModule  
  ],  
  providers: [],  
  bootstrap: [AppComponent]  
})  
export class AppModule { }

接下来，生成一个组件:

$ ng generate component home

接下来，生成一个上传服务:

$ ng generate service upload

接下来，打开src/app/upload.service。Ts文件如下:

import { HttpClient, HttpEvent, HttpErrorResponse, HttpEventType } from  '@angular/common/http';  
import { map } from  'rxjs/operators';

@Injectable({  
  providedIn: 'root'  
})  
export class UploadService { 
    SERVER_URL: string = "https://file.io/";  
    constructor(private httpClient: HttpClient) { }
    public upload(formData) {

      return this.httpClient.post<any>(this.SERVER_URL, formData, {  
         reportProgress: true,  
         observe: 'events'  
      });  
   }
}

接下来，打开src/app/home/home.component.ts文件，开始添加以下导入:

import { Component, OnInit, ViewChild, ElementRef  } from '@angular/core';
import { HttpEventType, HttpErrorResponse } from '@angular/common/http';
import { of } from 'rxjs';  
import { catchError, map } from 'rxjs/operators';  
import { UploadService } from  '../upload.service';

接下来，定义fileUpload和files变量，并注入UploadService，如下所示:

@Component({  
  selector: 'app-home',  
  templateUrl: './home.component.html',  
  styleUrls: ['./home.component.css']  
})  
export class HomeComponent implements OnInit {
    @ViewChild("fileUpload", {static: false}) fileUpload: ElementRef;files  = [];  
    constructor(private uploadService: UploadService) { }

接下来，定义uploadFile()方法:

uploadFile(file) {  
    const formData = new FormData();  
    formData.append('file', file.data);  
    file.inProgress = true;  
    this.uploadService.upload(formData).pipe(  
      map(event => {  
        switch (event.type) {  
          case HttpEventType.UploadProgress:  
            file.progress = Math.round(event.loaded * 100 / event.total);  
            break;  
          case HttpEventType.Response:  
            return event;  
        }  
      }),  
      catchError((error: HttpErrorResponse) => {  
        file.inProgress = false;  
        return of(`${file.data.name} upload failed.`);  
      })).subscribe((event: any) => {  
        if (typeof (event) === 'object') {  
          console.log(event.body);  
        }  
      });  
  }

接下来，定义uploadFiles()方法，该方法可用于上传多个图像文件:

private uploadFiles() {  
    this.fileUpload.nativeElement.value = '';  
    this.files.forEach(file => {  
      this.uploadFile(file);  
    });  
}

接下来，定义onClick()方法:

onClick() {  
    const fileUpload = this.fileUpload.nativeElement;fileUpload.onchange = () => {  
    for (let index = 0; index < fileUpload.files.length; index++)  
    {  
     const file = fileUpload.files[index];  
     this.files.push({ data: file, inProgress: false, progress: 0});  
    }  
      this.uploadFiles();  
    };  
    fileUpload.click();  
}

接下来，我们需要创建图像上传UI的HTML模板。打开src/app/home/home.component.html文件，添加以下内容:

<div [ngStyle]="{'text-align':center; 'margin-top': 100px;}">
   <button mat-button color="primary" (click)="fileUpload.click()">choose file</button>  
   <button mat-button color="warn" (click)="onClick()">Upload</button>  
   <input [hidden]="true" type="file" #fileUpload id="fileUpload" name="fileUpload" multiple="multiple" accept="image/*" />
</div>

看看这篇教程和这篇文章

就我个人而言，我使用ngx-material-file-input作为前端，Firebase作为后端。更准确地说，后端是与Cloud Firestore结合的Cloud Storage for Firebase。下面是一个示例，它限制文件不大于20 MB，并且只接受某些文件扩展名。我还使用Cloud Firestore来存储上传文件的链接，但你可以跳过这个。

contact.component.html

<mat-form-field>
  <!--
    Accept only files in the following format: .doc, .docx, .jpg, .jpeg, .pdf, .png, .xls, .xlsx. However, this is easy to bypass, Cloud Storage rules has been set up on the back-end side.
  -->
  <ngx-mat-file-input
    [accept]="[
      '.doc',
      '.docx',
      '.jpg',
      '.jpeg',
      '.pdf',
      '.png',
      '.xls',
      '.xlsx'
    ]"
    (change)="uploadFile($event)"
    formControlName="fileUploader"
    multiple
    aria-label="Here you can add additional files about your project, which can be helpeful for us."
    placeholder="Additional files"
    title="Additional files"
    type="file"
  >
  </ngx-mat-file-input>
  <mat-icon matSuffix>folder</mat-icon>
  <mat-hint
    >Accepted formats: DOC, DOCX, JPG, JPEG, PDF, PNG, XLS and XLSX,
    maximum files upload size: 20 MB.
  </mat-hint>
  <!--
    Non-null assertion operators are required to let know the compiler that this value is not empty and exists.
  -->
  <mat-error
    *ngIf="contactForm.get('fileUploader')!.hasError('maxContentSize')"
  >
    This size is too large,
    <strong
      >maximum acceptable upload size is
      {{
        contactForm.get('fileUploader')?.getError('maxContentSize')
          .maxSize | byteFormat
      }}</strong
    >
    (uploaded size:
    {{
      contactForm.get('fileUploader')?.getError('maxContentSize')
        .actualSize | byteFormat
    }}).
  </mat-error>
</mat-form-field>

ts(大小验证器部分)

import { FileValidator } from 'ngx-material-file-input';
import { FormBuilder, FormGroup, Validators } from '@angular/forms';

/**
 * @constructor
 * @description Creates a new instance of this component.
 * @param  {formBuilder} - an abstraction class object to create a form group control for the contact form.
 */
constructor(
  private angularFirestore: AngularFirestore,
  private angularFireStorage: AngularFireStorage,
  private formBuilder: FormBuilder
) {}

public maxFileSize = 20971520;
public contactForm: FormGroup = this.formBuilder.group({
    fileUploader: [
      '',
      Validators.compose([
        FileValidator.maxContentSize(this.maxFileSize),
        Validators.maxLength(512),
        Validators.minLength(2)
      ])
    ]
})

ts(文件上传器部分)

import { AngularFirestore } from '@angular/fire/firestore';
import {
  AngularFireStorage,
  AngularFireStorageReference,
  AngularFireUploadTask
} from '@angular/fire/storage';
import { catchError, finalize } from 'rxjs/operators';
import { throwError } from 'rxjs';

public downloadURL: string[] = [];
/**
* @description Upload additional files to Cloud Firestore and get URL to the files.
   * @param {event} - object of sent files.
   * @returns {void}
   */
  public uploadFile(event: any): void {
    // Iterate through all uploaded files.
    for (let i = 0; i < event.target.files.length; i++) {
      const randomId = Math.random()
        .toString(36)
        .substring(2); // Create random ID, so the same file names can be uploaded to Cloud Firestore.

      const file = event.target.files[i]; // Get each uploaded file.

      // Get file reference.
      const fileRef: AngularFireStorageReference = this.angularFireStorage.ref(
        randomId
      );

      // Create upload task.
      const task: AngularFireUploadTask = this.angularFireStorage.upload(
        randomId,
        file
      );

      // Upload file to Cloud Firestore.
      task
        .snapshotChanges()
        .pipe(
          finalize(() => {
            fileRef.getDownloadURL().subscribe((downloadURL: string) => {
              this.angularFirestore
                .collection(process.env.FIRESTORE_COLLECTION_FILES!) // Non-null assertion operator is required to let know the compiler that this value is not empty and exists.
                .add({ downloadURL: downloadURL });
              this.downloadURL.push(downloadURL);
            });
          }),
          catchError((error: any) => {
            return throwError(error);
          })
        )
        .subscribe();
    }
  }

storage.rules

rules_version = '2';
service firebase.storage {
  match /b/{bucket}/o {
    match /{allPaths=**} {
        allow read; // Required in order to send this as attachment.
      // Allow write files Firebase Storage, only if:
      // 1) File is no more than 20MB
      // 2) Content type is in one of the following formats: .doc, .docx, .jpg, .jpeg, .pdf, .png, .xls, .xlsx.
      allow write: if request.resource.size <= 20 * 1024 * 1024
        && (request.resource.contentType.matches('application/msword')
        || request.resource.contentType.matches('application/vnd.openxmlformats-officedocument.wordprocessingml.document')
        || request.resource.contentType.matches('image/jpg')
        || request.resource.contentType.matches('image/jpeg')
        || request.resource.contentType.matches('application/pdf')
                || request.resource.contentType.matches('image/png')
        || request.resource.contentType.matches('application/vnd.ms-excel')
        || request.resource.contentType.matches('application/vnd.openxmlformats-officedocument.spreadsheetml.sheet'))
    }
  }
}