拖放图片上传，角度4

Question

我创建了一个拖放虚假上传服务。我可以记录图片的宽度和高度以及网址。但图像不上传。 问题是如果我想记录，我上传函数中的'img'是未定义的。我怎样才能解决这个问题？为什么没有定义？

import { Injectable } from '@angular/core'; 
import { Observable } from 'rxjs/Rx'; 

@Injectable() 
export class DragNDropService { 

    constructor() { 
    } 

    upload(formData: any) { 
     const photos: any[] = formData.getAll('photos'); 
     const promises = photos.map((x: File) => this.getImage(x) 
      .then(img => { 
       return({ 
       id: img, 
       originalName: x.name, 
       fileName: x.name, 
       url: img 
      })})); 
     return Observable.fromPromise(Promise.all(promises)); 
    } 

    private getImage(file: File) { 
     const fReader = new FileReader(); 
     const img = document.createElement('img'); 

     const readFile = new Promise((resolve, reject) => { 
      fReader.onload =() => { 
       resolve(img.src = fReader.result); 
      } 
      fReader.readAsDataURL(file); 
     }) 

     const readImg = new Promise((resolve, reject) => { 
      img.onload =() => { 
       resolve(img) 
      } 
     }) 

     return Promise.all([readFile, readImg]).then(img => { 
      this.getBase64Image(img) 
     }) 
    } 

    private getBase64Image(img) { 
     const canvas = document.createElement('canvas'); 
     console.log(img[1].width) 
     console.log(img[1].height) 

     canvas.width = img[1].width; 
     canvas.height = img[1].height; 

     const ctx = canvas.getContext('2d'); 
     console.log(img) 
     ctx.drawImage(img[1], 0, 0); 

     const dataURL = canvas.toDataURL('image/png'); 
     return dataURL; 
    } 

} 

Answer 1

我想通了，问题是我没有真正返回img。

这是的getImage功能我的新return语句：

return Promise.all([readFile, readImg]).then(img => this.getBase64Image(img))