如何使用Typescript和Angular 4显示图像

Question

我对打字稿和网页开发很新,所以如果我的代码很糟糕,我很抱歉.无论如何,我在显示配置文件图片上传的"预览图像"时遇到问题.我正在使用ng2-file-upload将我的图像上传到服务器,该部分工作正常.在我点击上传按钮之前,我想在选择后立即在页面上显示所选图像.目前我试图通过从HTMLImageElement检索src属性来显示图像,但src属性似乎是空的.

import { Component, OnInit } from '@angular/core';
import {  FileUploader } from 'ng2-file-upload/ng2-file-upload';

const URL = 'http://localhost:4200/api/upload';

@Component({
  selector: 'app-view-profile',
  templateUrl: './view-profile.component.html',
  styleUrls: ['./view-profile.component.css']
})
export class ViewProfileComponent implements OnInit {

  constructor() { }
  public uploader: FileUploader = new FileUploader({url: URL, itemAlias: 'newProfilePicture'});
  title: string;
  previewImage: any;
  tempImage: any;
  source: string;

  imagePreview(input) 
  {
      document.getElementById("previewImage").style.display="block";
      
        console.log("Image is selected")
        this.previewImage = document.getElementById("previewImage");
        console.log(this.previewImage);
        
        this.source = (<HTMLImageElement>document.getElementById('previewImage')).src
        console.log("Image Source: " + this.source + " Should be inbetween here");
        
      
      //var reader = new FileReader();
        
        //console.log(this.previewImage);
      
  }

  ngOnInit() {
  	this.title = 'View or Update Your Profile';
  	this.uploader.onAfterAddingFile = (file)=> {file.withCredentials = false;};
  	this.uploader.onCompleteItem = (item:any, response:any, status:any, headers:any) => {
        console.log("ImageUpload:uploaded:", item, status, response);
    //this.imagePreview();


    };
  }


}

这是我的HTML

<div class="container">
    <h1>{{title}}</h1>

    <div>

        <input type="file" id="previewImage" (change)="imagePreview(this);" name="newProfilePicture" ng2FileSelect [uploader] ="uploader" />
        <button type="button" class="btn btn-success btn-s" (click)="uploader.uploadAll()" [disabled]="!uploader.getNotUploadedItems().length">
          Upload Your File
        </button>
    </div>
</div>

Answer 1

你通过这个简单的功能实现了这个目标:

模板:

<img [src]="url" height="200"> <br/>
<input type='file' (change)="onSelectFile($event)">

零件 :

onSelectFile(event) { // called each time file input changes
    if (event.target.files && event.target.files[0]) {
      var reader = new FileReader();

      reader.readAsDataURL(event.target.files[0]); // read file as data url

      reader.onload = (event) => { // called once readAsDataURL is completed
        this.url = event.target.result;
      }
    }
}

以下是它的工作示例,请查看以下内容:

工作演示

Answer 2

模板 ：

<input type='file' (change)="readUrl($event)">
<img [src]="url">

成分 ：

 readUrl(event:any) {
      if (event.target.files && event.target.files[0]) {
          var reader = new FileReader();

          reader.onload = (event:any) => {
              this.url = event.target.result;
          }

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

T 试过了，它没有任何错误。