Analysis of application examples of custom transition functions in Vue documents

Vue custom transition functions are used to control the specific behavior of transition effects when elements are inserted, updated, and deleted. This function accepts a parameter object, including the element to be transitioned, the transition class name, and the callback function to complete the transition.

In Vue, transition effects can be achieved through CSS class names. When Vue handles transition effects, it will add transition class names to elements in a certain order, thereby triggering animation effects. For example, the "v-enter" and "v-enter-active" class names are added when the element is inserted and removed after the element is inserted.

However, Vue’s default transition effect is a bit monotonous and difficult to meet the needs of various scenarios. At this point, we can use the custom transition function provided in Vue to achieve a more free and flexible transition effect.

Below, we use an example to introduce the use of custom transition functions in detail.

Custom transition function example

We take a picture carousel component as an example to demonstrate how to use Vue to customize the transition function. This component can realize automatic carousel and manual switching of pictures. We will use a custom transition function to achieve the transition effect of the image.

Component template

First, we define a carousel component template, which contains a display image and a button for manually switching images:

<template>
  <div class="carousel">
    <transition @before-enter="beforeEnter" @enter="enter" @leave="leave">
      <img :src="currentImg" key="currentImg" class="image" />
    </transition>
    <div class="button-group">
      <button @click="prev">Prev</button>
      <button @click="next">Next</button>
    </div>
  </div>
</template>

Component data and functions

Next, we define the data, calculated properties and methods of the component:

<script>
export default {
  data() {
    return {
      imgs: [
        "https://placekitten.com/g/300/200",
        "https://placekitten.com/g/300/210",
        "https://placekitten.com/g/300/220"
      ],
      currentIndex: 0
    };
  },
  computed: {
    currentImg() {
      return this.imgs[this.currentIndex];
    }
  },
  methods: {
    prev() {
      this.currentIndex = (this.currentIndex - 1 + this.imgs.length) % this.imgs.length;
    },
    next() {
      this.currentIndex = (this.currentIndex + 1) % this.imgs.length;
    },
    beforeEnter(el) {
      el.style.opacity = 0;
    },
    enter(el, done) {
      const delay = el.dataset.index * 1000;
      setTimeout(() => {
        el.style.transition = "opacity 1s";
        el.style.opacity = 1;
        done();
      }, delay);
    },
    leave(el, done) {
      el.style.transition = "opacity 1s";
      el.style.opacity = 0;
      setTimeout(() => {
        done();
      }, 1000);
    }
  }
};
</script>

Among them, the imgs array contains all the image links that need to be rotated, and currentIndex represents the currently displayed image index. The currentImg function returns the link to the current image.

The prev and next methods are used to switch pictures manually. beforeEnter, enter and leave are custom transition functions, corresponding to the transition effects during element insertion, update and deletion respectively.

In the enter transition function, we use setTimeout to achieve the effect of displaying each picture at different time points. In the leave transition function, we use a delay function to wait for the animation effect to complete before destroying the element node.

Summary

Through the above example, we can see that in the Vue custom transition function, we can control the specific implementation of the transition effect through the passed el parameter. In actual development, we can customize different transition functions according to specific needs to achieve a more flexible and free transition effect.

Finally, it should be noted that Vue's custom transition function must be executed before the transition class name is added to the element, otherwise no transition effect will be triggered.

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