Angular img loading directive

问题:

I am trying to make a simple directive. When the image is loading, the img src will be set to an @Input() string field. On load, the image will be set to the original src value (or at least how I am trying to implement it).

I was using the answer here: https://stackoverflow.com/a/38837619/843443 but is isn't a directive, and thus would require a number of changes wherever I use images.

My first attempt:

loading-img.directive.ts:

import { Directive, ElementRef, HostListener, Input } from '@angular/core';

@Directive({
  selector: '[tohLoadingImg]'
})
export class LoadingImgDirective {
  imgSrc: String;

  @Input()
  spinnerSrc: String;

  constructor(private el: ElementRef) {
    this.imgSrc = el.nativeElement.src;
    el.nativeElement.src = this.spinnerSrc;
  }

  @HostListener('load') onLoad() {
    this.el.nativeElement.src = this.imgSrc;
  }

}

from:

 <img src="{{hero.imgUrl}}" alt="Random first slide">

to:

<img src="{{hero.imgUrl}}" alt="Random first slide" [tohLoadingImg]="'/assets/ring.svg'">

Error:

Can't bind to 'tohLoadingImg' since it isn't a known property of 'img'. (".imgUrl}}" alt="Random first slide">-->

What am I missing?

回答1:

Try this

import {
  Directive,
  Attribute,
  Renderer2,
  ElementRef,
  HostListener } from '@angular/core';

@Directive({
  selector: '[uiImageLoader]'
})
export class UiImageLoaderDirective {
  constructor(
    @Attribute('loader') public loader: string,
    @Attribute('onErrorSrc') public onErrorSrc: string,
    private renderer: Renderer2,
    private el: ElementRef) {
      this.renderer.setAttribute(this.el.nativeElement, 'src', this.loader);
    }

  @HostListener('load') onLoad() {
    this.renderer.setAttribute(this.el.nativeElement, 'src', this.el.nativeElement.src);
  }
  @HostListener('error') onError() {
    this.renderer.setAttribute(this.el.nativeElement, 'src', this.onErrorSrc);
  }
}

USAGE

<img
  uiImageLoader
  onErrorSrc="/assets/images/no-available-800.png"
  loader="/assets/images/image-loader.svg"
  [src]="post.imagePath" [alt]="post.title">

回答2:

Thanks to @Aravind for the direction. This is how I solved it (by using a component rather than a directive):

spinner-img.component.ts:

import { Component, OnInit, Input } from '@angular/core';

@Component({
  selector: 'toh-spinner-img',
  templateUrl: './spinner-img.component.html',
  styleUrls: ['./spinner-img.component.scss']
})
export class SpinnerImgComponent implements OnInit {

  @Input() imgSrc: String;
  @Input() spinnerSrc: String;
  @Input() imgContainerClass: String;

  loading: boolean = true

  onLoad() {
    this.loading = false;
  }

  constructor() { }

  ngOnInit() { }

}

spinner-img.component.html:

<div [class]="imgContainerClass">
  <img *ngIf="loading" src="{{spinnerSrc}}" alt="loading"/>
  <img [hidden]="loading" (load)="onLoad()" src="{{imgSrc}}" alt="Hero Pic"/>
</div>

And in use:

 <toh-spinner-img [imgSrc]="hero.imgUrl" [spinnerSrc]="'/assets/ring.svg'"></toh-spinner-img>