How to implement lazy loading of images in uniapp

How to implement the lazy loading function of images in uniapp

In modern mobile applications and web page development, images are an indispensable element. However, due to the limitations of mobile networks and user experience requirements, loading a large number of images at the same time may cause the loading speed of applications or web pages to slow down, affecting the user experience. In order to solve this problem, you can use the lazy loading technology of images, which can delay loading of images and only start loading when they enter the user's visible area, improving the page loading speed and user experience.

UniApp is a cross-platform application development framework based on Vue.js. It can simultaneously generate applications running on iOS, Android, H5 and other platforms. In UniApp, you can use some plug-ins and technologies to implement lazy loading of images. The following will demonstrate how to use the vue-lazyload plug-in and Intersection Observer API to implement lazy loading of images.

First, install the vue-lazyload plug-in in the UniApp project. Open the command line tool, switch to the root directory of your UniApp project, and run the following command:

npm install vue-lazyload

After the installation is complete, introduce the relevant styles in the uni.scss file ：

@import 'path/to/node_modules/vue-lazyload/style/uni.scss';

Then, use the v-lazy instruction in the image component that needs to be lazy loaded to delay loading images. For example:

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where imageUrl is the address of the image. In this way, when the image enters the user's visible area, the image will start loading, improving the loading speed of the page.

Next, in order to achieve the effect of loading the image when it enters the user's visual area, we can use the Intersection Observer API. First, initialize the Intersection Observer object in the component's life cycle hook function and monitor the visibility of the image element. For example:

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export default {

mounted() {
  const observer = new IntersectionObserver((entries) => {
    entries.forEach((entry) => {
      if (entry.isIntersecting) {
        this.loadImage(entry.target);
      }
    });
  });

  const lazyImages = document.querySelectorAll('img[v-lazy]');
  lazyImages.forEach((lazyImage) => {
    observer.observe(lazyImage);
  });
},

methods: {
  loadImage(image) {
    image.src = image.dataset.src;
  },
},

}
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In the mounted life cycle hook function, create an Intersection Observer object and pass in a callback function. This callback function is triggered when the observed element enters or leaves the user's visual area. In the callback function, traverse the list of observed elements. If the element enters the user's visible area, call the loadImage method to load the image.

In the loadImage method, assign the data-src attribute of the image to the src attribute of the image, so that the image starts loading.

The above are the steps to use the vue-lazyload plug-in and Intersection Observer API to implement the image lazy loading function in UniApp. By delaying the loading of images, the page loading time can be greatly reduced and the user experience improved. Of course, in actual development, the implementation of lazy loading of images needs to be adjusted and optimized according to the specific needs of the project.

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