Ionic 2 / Ionic 3 / Ionic 4 : (Lazy) Loading spinner for pictures

问题

I'm using ion-img in my ionic2 application to load my pictures correctly. However, I wonder if there is a way to indicate to the user that the picture is actually loading.

Thank you for your help!

EDIT : Here is the answer if you absolutely need to use the ion-img tag. If not, you should use ionic-image-loader as AdminDev826 suggested.

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;
}

I hope it can help someone!

回答1:

Please use ionic-image-loader plugin

Install the NPM Package
```
npm install --save ionic-image-loader
```

Install Required Plugins

npm i --save @ionic-native/file

ionic plugin add cordova-plugin-file --save

npm i --save @ionic-native/transfer
ionic plugin add cordova-plugin-file-transfer --save

Import IonicImageLoader module

Add IonicImageLoader.forRoot() in your app's root module

import { IonicImageLoader } from 'ionic-image-loader';

// import the module
@NgModule({
 ...
  imports: [
    IonicImageLoader.forRoot()
  ]
})
export class AppModule {}

Then add IonicImageLoader in your child/shared module(s)

import { IonicImageLoader } from 'ionic-image-loader';

@NgModule({
...
  imports: [
    IonicImageLoader
  ]
})
export class SharedModule {}

回答2:

Here is my solution :

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

And my CSS :

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

I hope it can help someone!

回答3:

If you want to use the img tag instead of ion-img here is the solution:

  <img src="{{image.src}}" (load)="loaded = true" [ngClass]="{'img-loaded':loaded}" [hidden]="!loaded" *ngIf="image_exists" />
  <ion-spinner [ngClass]="{'center':true}" *ngIf="!loaded"></ion-spinner>

In your CSS file you should write the following:

 .img-loaded + ion-spinner {
  display:none;
}
// .center in my case to make the spinner at the center
.center{
  margin-left: auto;
  margin-right: auto;
  display: block;
}

loaded is a boolean variable with false default value you have to define in your component.

回答4:

Your solution is not the best one because the app still downloads all the images, For example in a Facebook like app, You will be downloading all the images from the Feed to your app, This will make everything super slow.

Use this: https://github.com/NathanWalker/ng2-image-lazy-load

来源：https://stackoverflow.com/questions/38846271/ionic-2-ionic-3-ionic-4-lazy-loading-spinner-for-pictures

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