图像加载时显示“正在加载”图标

Question

I want to show a background image/loading spinner inside a div that will load an image inside of it, the image will show once it's fully loaded doing something like this:

   <div style="background-image:url('imageThatWillAppearBeforeLoad')"></div>

Demo (In jQuery)

How can I have the same using Angular2/Ionic2?

Answer 1

Create a component that shows the placeholder image until the requested image is loaded, and hides the requested image. Once the image is loaded, you hide the placeholder and show the image.

@Component({
  selector: 'image-loader',
  template: `<img *ngIf="!loaded" src="url-to-your-placeholder"/>
    <img [hidden]="!loaded" (load)="loaded = true" [src]="src"/>`
})
export class ImageLoader {
  @Input() src;
}

See it working in Plunker .

Update

Now that I understand the requirements better, here's a solution with background image. It's a little hacky, and I like the original one better...

@Directive({
  selector: '[imageLoader]'
})
export class ImageLoader {
  @Input() imageLoader;

  constructor(private el:ElementRef) {
    this.el = el.nativeElement;
    this.el.style.backgroundImage = "url(http://smallenvelop.com/demo/image-loading/spinner.gif)";
  }

  ngOnInit() {
    let image = new Image();
    image.addEventListener('load', () => {
      this.el.style.backgroundImage = `url(${this.imageLoader})`;
    });
    image.src = this.imageLoader;
  }
}

Updated plunker .

Answer 2

Here is a copy of one of my posts

I finally solved that problem with CSS! When an image is loading in ionic 2, the ion-img tag doesn't have any class. However, when the image is finally loaded, the ion-img tag get the class "img-loaded".

Here is my solution :

  <ion-img [src]="img.src"></ion-img>
  <ion-spinner></ion-spinner>

And my CSS :

.img-loaded + ion-spinner {
  display:none;
}

Answer 3

Simply use this function

loadImage(element: HTMLElement, imagePath: string, spinnerPath: string) {
  element.tagName === 'img'
    ? element.setAttribute('src', spinnerPath)
    : (element.style.background = `url(${spinnerPath}) 50% 50% no-repeat`);
  const image = new Image();
  image.crossOrigin = 'Anonymous';
  image.src = imagePath;
  image.onload = () => {
    element.tagName === 'img'
      ? element.setAttribute('src', imagePath)
      : (element.style.background = `url(${imagePath})`);
  };
}

You don't have to worry about your element is image or div or whatever it is?

example if you didn't figure out how to use it

ngOnInit() {
  const myElement = document.getElementsByClassName('my-element')[0];
  // or however you want to select it.
  const imagePath = 'path/to/image.png';
  const spinnerPath = 'path/to/spinner.gif'; // or base64 spinner url.

  this.loadImage(myElement, imagePath, spinnerPath);
}

Happy coding 😉