要实现Angular 8与Web API文件上传，可以按照以下步骤进行操作：

1. 在Angular项目中创建一个服务，用于处理文件上传操作。可以使用Angular的HttpClient模块来发送HTTP请求。

import { Injectable } from '@angular/core';
import { HttpClient } from '@angular/common/http';

@Injectable({
    providedIn: 'root'
})
export class FileUploadService {
    constructor(private http: HttpClient) { }

    uploadFile(file: File) {
        const formData = new FormData();
        formData.append('file', file);

        return this.http.post('/api/upload', formData);
    }
}

2. 在Web API中创建一个控制器，用于接收文件上传请求并保存文件。

using Microsoft.AspNetCore.Http;
using Microsoft.AspNetCore.Mvc;
using System.IO;
using System.Threading.Tasks;

[Route("api/[controller]")]
[ApiController]
public class UploadController : ControllerBase
{
    [HttpPost]
    public async Task Upload(IFormFile file)
    {
        if (file == null || file.Length == 0)
            return BadRequest("No file uploaded.");

        var filePath = Path.Combine(Directory.GetCurrentDirectory(), "uploads", file.FileName);

        using (var stream = new FileStream(filePath, FileMode.Create))
        {
            await file.CopyToAsync(stream);
        }

        return Ok();
    }
}

3. 在Angular组件中调用文件上传服务。

import { Component } from '@angular/core';
import { FileUploadService } from './file-upload.service';

@Component({
    selector: 'app-file-upload',
    template: `
        
        Upload
    `
})
export class FileUploadComponent {
    selectedFile: File;

    constructor(private fileUploadService: FileUploadService) { }

    onFileSelected(event) {
        this.selectedFile = event.target.files[0];
    }

    uploadFile() {
        this.fileUploadService.uploadFile(this.selectedFile).subscribe(
            () => {
                console.log('File uploaded successfully.');
            },
            error => {
                console.error('Error uploading file:', error);
            }
        );
    }
}

以上代码示例实现了Angular 8与Web API文件上传功能。在Angular组件中，用户可以选择文件并点击“Upload”按钮来触发文件上传操作。文件将被发送到Web API的“/api/upload”端点，然后在服务器端保存到指定路径。上传过程中可能会出现错误，因此需要适当处理错误情况。