Implementation method of lazy loading of images developed in PHP in WeChat mini program

With the rapid development of mobile Internet, mini programs, as a new application form, are favored by more and more people. In the development of small programs, image display is a very common requirement, and lazy loading is one of the very useful techniques.

What is lazy loading?

Lazy loading means loading images when the page scrolls to the visible area to improve page loading speed and user experience. In WeChat mini programs, the use of lazy loading technology can reduce traffic and save bandwidth when the page is opened. It can also improve the user experience and make users feel that the page loads faster.

How to implement lazy loading of images in WeChat applet?

We can implement lazy loading of images by using PHP scripts in mini programs. When the user opens the applet, the PHP script will traverse all the images that need to be lazy loaded and store the URL of each image in an array. When the user scrolls the page, the applet will issue an AJAX request, obtain the array storing the image URL from the server, and load the image corresponding to the position of the image that needs to be lazy loaded.

The specific implementation steps are as follows:

1. Traverse all images that need to be lazy loaded and store the URL of each image in an array. The PHP code is as follows:

$urls = array();
$imgs = glob("images/*.jpg");
foreach($imgs as $img) {
    $url = "http://example.com/".$img;
    array_push($urls, $url);
}

2. Issue an AJAX request in the applet to obtain an array storing image URLs from the server. The applet uses the wx.request method to issue an AJAX request, and sets the responseType to json. The code is as follows:

wx.request({
    url: 'http://example.com/geturls.php',
    method: 'GET',
    responseType: 'json',
    success: function(res) {
        var urls = res.data.urls;
    }
})

3. Listen to the page scroll event and load the image corresponding to the position according to the position of the image that needs to be lazy loaded. The applet uses the wx.createIntersectionObserver method to monitor page scrolling events and determine whether the image that needs to be loaded lazily enters the visible area.
4. In the listener's observe method, determine whether the image that needs to be loaded lazily enters the visible area. If so, assign the URL of the image to the src attribute of the corresponding image tag to implement lazy loading of the image. . The code is as follows:

var observer = wx.createIntersectionObserver();
observer.relativeToViewport({bottom: 100}).observe('.lazyload', (res) => {
    if (res.intersectionRatio > 0) {
        var index = res.dataset.index;
        var url = urls[index];
        var img = this.data.list[index];
        img.src = url;
        this.setData({
            list: this.data.list
        });
    }
})

Summary

The above is how to use PHP scripts to implement lazy loading of images in WeChat mini programs. Using lazy loading technology can improve page loading speed and user experience, reduce traffic when the page is opened, and save bandwidth. I hope this article can inspire everyone's practice in mini program development.

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