How to detect sliding stop in vue

In front-end development, the use trend of mobile pages is gradually growing. At the same time, the operation method of mobile terminal is also different from that of PC terminal. Sliding has become one of the most frequent operations of users. Sliding is not only used when browsing the web, but also commonly used in various applications, such as reading news, browsing products, watching videos, etc. Therefore, how to effectively detect sliding stop has become a problem that many front-end engineers need to solve.

Vue is one of the most popular front-end frameworks at the moment, and more and more developers are using Vue for mobile development. This article will introduce how to use Vue to detect sliding stop.

1. Introduction to sliding events

In mobile terminal development, we mainly use two events to detect sliding: touchstart and touchmove. When the finger touches the screen, the touchstart event is triggered; when the finger slides on the screen, the touchmove event is triggered. We can get the sliding direction and distance by listening to these two events and obtaining the coordinate information of the finger on the screen, and then calculating the movement distance of the finger.

2. Detection method of sliding stop

In Vue, we can use custom instructions to listen for sliding events. Custom directives are a very useful feature in Vue, which can easily bind events and attributes directly to DOM elements.

The following is a simple example. We can add a v-touchend instruction to an element. This instruction will be triggered when the finger leaves the screen, and the direction and distance of the finger sliding can be obtained in the instruction.

Vue.directive('touchend', {
  bind: function(el, binding) {
    let startX, startY;
    el.addEventListener('touchstart', function(event) {
      startX = event.touches[0].clientX;
      startY = event.touches[0].clientY;
    });
    el.addEventListener('touchend', function(event) {
      let endX = event.changedTouches[0].clientX;
      let endY = event.changedTouches[0].clientY;
      let distanceX = endX - startX;
      let distanceY = endY - startY;
      let direction = '';
      if (Math.abs(distanceX) < Math.abs(distanceY)) {
        // 垂直方向滑动
        if (distanceY < 0) {
          direction = &#39;up&#39;;
        } else {
          direction = &#39;down&#39;;
        }
      } else {
        // 水平方向滑动
        if (distanceX < 0) {
          direction = &#39;left&#39;;
        } else {
          direction = &#39;right&#39;;
        }
      }
      binding.value(direction, distanceX, distanceY);
    });
  }
});

In this example, we use the bind hook function to register the command, then listen to the touchstart and touchend events through the addEventListener method, calculate the distance and direction of the finger slide, and pass the results to the function bound to the command.

3. Application scenarios of sliding stop

In mobile development, there are many application scenarios that need to detect sliding stop, such as pull-down to refresh, pull-up to load, etc. We can implement these functions by triggering corresponding events when a sliding stop is detected.

Taking pull-down refresh as an example, we can add a pull-down icon to the element bound to the v-touchend instruction. It will appear when the user pulls down to a certain distance, and the pull-down refresh event will be automatically triggered when the user lets go.

Vue.directive('pull-refresh', {
  bind: function(el, binding) {
    let startX, startY;
    let refreshHeight = 60; // 下拉刷新高度
    let refreshIcon = document.createElement('img');
    refreshIcon.src = 'https://xxx.com/icons/refresh.png';
    refreshIcon.width = 40;
    refreshIcon.height = 40;
    refreshIcon.style.display = 'none';
    refreshIcon.style.marginLeft = '-20px';
    refreshIcon.style.position = 'absolute';
    refreshIcon.style.top = '-50px';
    el.appendChild(refreshIcon);
    el.addEventListener('touchstart', function(event) {
      startX = event.touches[0].clientX;
      startY = event.touches[0].clientY;
    });
    el.addEventListener('touchmove', function(event) {
      let endY = event.changedTouches[0].clientY;
      let distanceY = endY - startY;
      if (distanceY > refreshHeight) {
        refreshIcon.style.display = 'block';
        binding.value();
      } else {
        refreshIcon.style.display = 'none';
      }
    });
  }
});

In this example, we use a custom instruction v-pull-refresh. After binding this instruction to the element, the pull-down refresh event will be triggered when the user pulls down more than 60 pixels.

4. Summary

This article briefly introduces the mobile terminal sliding event and how to add custom instructions in Vue to detect sliding stop to achieve pull-down refresh and other functions. In addition to pull-down refresh, sliding stop can also be used to achieve pull-up loading, image carousel and other effects. Mastering these sliding control skills will be of great help in improving the user experience of mobile applications.

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