js 实现拖拽排序

前言

拖拽排序对于小伙伴们来说应该不陌生，平时工作的时候，可能会选择使用类似Sortable.js这样的开源库来实现需求。但在完成需求后，大家有没有没想过拖拽排序是如何实现的呢？我花了点时间研究了一下，今天分享给大家。

实现

CSS

* {
    margin: 0;
    padding: 0;
    box-sizing: border-box;
}

.grid {
    display: flex;
    flex-wrap: wrap;
    margin: 0 -15px -15px 0;
    touch-action: none;
    user-select: none;
}

.grid-item {
    width: 90px;
    height: 90px;
    line-height: 88px;
    text-align: center;
    margin: 0 15px 15px 0;
    background: #FFF;
    border: 1px solid #d6d6d6;
    list-style: none;
}

.active {
    background: #c8ebfb;
}

.clone-grid-item {
    position: fixed;
    left: 0;
    top: 0;
    z-index: 1;
    width: 90px;
    height: 90px;
    line-height: 88px;
    text-align: center;
    background: #FFF;
    border: 1px solid #d6d6d6;
    opacity: 0.8;
    list-style: none;
}

HTML

<ul class="grid">
    <li class="grid-item">item1</li>
    <li class="grid-item">item2</li>
    <li class="grid-item">item3</li>
    <li class="grid-item">item4</li>
    <li class="grid-item">item5</li>
    <li class="grid-item">item6</li>
    <li class="grid-item">item7</li>
    <li class="grid-item">item8</li>
    <li class="grid-item">item9</li>
    <li class="grid-item">item10</li>
</ul>

js

采用ES6 Class写法

class Draggable {
    constructor(options) {
        this.parent = options.element; // 父级元素
        this.cloneElementClassName = options.cloneElementClassName; // 克隆元素类名
        this.isPointerdown = false;
        this.diff = { x: 0, y: 0 }; // 相对于上一次移动差值
        this.drag = { element: null, index: 0, lastIndex: 0 }; // 拖拽元素
        this.drop = { element: null, index: 0, lastIndex: 0 }; // 释放元素
        this.clone = { element: null, x: 0, y: 0 };
        this.lastPointermove = { x: 0, y: 0 };
        this.rectList = []; // 用于保存拖拽项getBoundingClientRect()方法获得的数据
        this.init();
    }
    init() {
        this.getRect();
        this.bindEventListener();
    }
    // 获取元素位置信息
    getRect() {
        this.rectList.length = 0;
        for (const item of this.parent.children) {
            this.rectList.push(item.getBoundingClientRect());
        }
    }
    handlePointerdown(e) {
        // 如果是鼠标点击，只响应左键
        if (e.pointerType === 'mouse' && e.button !== 0) {
            return;
        }
        if (e.target === this.parent) {
            return;
        }
        this.isPointerdown = true;
        this.parent.setPointerCapture(e.pointerId);
        this.lastPointermove.x = e.clientX;
        this.lastPointermove.y = e.clientY;
        this.drag.element = e.target;
        this.drag.element.classList.add('active');
        this.clone.element = this.drag.element.cloneNode(true);
        this.clone.element.className = this.cloneElementClassName;
        this.clone.element.style.transition = 'none';
        const i = [].indexOf.call(this.parent.children, this.drag.element);
        this.clone.x = this.rectList[i].left;
        this.clone.y = this.rectList[i].top;
        this.drag.index = i;
        this.drag.lastIndex = i;
        this.clone.element.style.transform = 'translate3d(' + this.clone.x + 'px, ' + this.clone.y + 'px, 0)';
        document.body.appendChild(this.clone.element);
    }
    handlePointermove(e) {
        if (this.isPointerdown) {
            this.diff.x = e.clientX - this.lastPointermove.x;
            this.diff.y = e.clientY - this.lastPointermove.y;
            this.lastPointermove.x = e.clientX;
            this.lastPointermove.y = e.clientY;
            this.clone.x += this.diff.x;
            this.clone.y += this.diff.y;
            this.clone.element.style.transform = 'translate3d(' + this.clone.x + 'px, ' + this.clone.y + 'px, 0)';
            for (let i = 0; i < this.rectList.length; i++) {
                // 碰撞检测
                if (e.clientX > this.rectList[i].left && e.clientX < this.rectList[i].right &&
                    e.clientY > this.rectList[i].top && e.clientY < this.rectList[i].bottom) {
                    this.drop.element = this.parent.children[i];
                    this.drop.lastIndex = i;
                    if (this.drag.element !== this.drop.element) {
                        if (this.drag.index < i) {
                            this.parent.insertBefore(this.drag.element, this.drop.element.nextElementSibling);
                            this.drop.index = i - 1;
                        } else {
                            this.parent.insertBefore(this.drag.element, this.drop.element);
                            this.drop.index = i + 1;
                        }
                        this.drag.index = i;
                        const dragRect = this.rectList[this.drag.index];
                        const lastDragRect = this.rectList[this.drag.lastIndex];
                        const dropRect = this.rectList[this.drop.index];
                        const lastDropRect = this.rectList[this.drop.lastIndex];
                        this.drag.lastIndex = i;
                        this.drag.element.style.transition = 'none';
                        this.drop.element.style.transition = 'none';
                        this.drag.element.style.transform = 'translate3d(' + (lastDragRect.left - dragRect.left) + 'px, ' + (lastDragRect.top - dragRect.top) + 'px, 0)';
                        this.drop.element.style.transform = 'translate3d(' + (lastDropRect.left - dropRect.left) + 'px, ' + (lastDropRect.top - dropRect.top) + 'px, 0)';
                        this.drag.element.offsetLeft; // 触发重绘
                        this.drag.element.style.transition = 'transform 150ms';
                        this.drop.element.style.transition = 'transform 150ms';
                        this.drag.element.style.transform = 'translate3d(0px, 0px, 0px)';
                        this.drop.element.style.transform = 'translate3d(0px, 0px, 0px)';
                    }
                    break;
                }
            }
        }
    }
    handlePointerup(e) {
        if (this.isPointerdown) {
            this.isPointerdown = false;
            this.drag.element.classList.remove('active');
            this.clone.element.remove();
        }
    }
    handlePointercancel(e) {
        if (this.isPointerdown) {
            this.isPointerdown = false;
            this.drag.element.classList.remove('active');
            this.clone.element.remove();
        }
    }
    bindEventListener() {
        this.handlePointerdown = this.handlePointerdown.bind(this);
        this.handlePointermove = this.handlePointermove.bind(this);
        this.handlePointerup = this.handlePointerup.bind(this);
        this.handlePointercancel = this.handlePointercancel.bind(this);
        this.getRect = this.getRect.bind(this);
        this.parent.addEventListener('pointerdown', this.handlePointerdown);
        this.parent.addEventListener('pointermove', this.handlePointermove);
        this.parent.addEventListener('pointerup', this.handlePointerup);
        this.parent.addEventListener('pointercancel', this.handlePointercancel);
        window.addEventListener('scroll', this.getRect);
        window.addEventListener('resize', this.getRect);
        window.addEventListener('orientationchange', this.getRect);
    }
    unbindEventListener() {
        this.parent.removeEventListener('pointerdown', this.handlePointerdown);
        this.parent.removeEventListener('pointermove', this.handlePointermove);
        this.parent.removeEventListener('pointerup', this.handlePointerup);
        this.parent.removeEventListener('pointercancel', this.handlePointercancel);
        window.removeEventListener('scroll', this.getRect);
        window.removeEventListener('resize', this.getRect);
        window.removeEventListener('orientationchange', this.getRect);
    }
}
// 实例化
new Draggable({
    element: document.querySelector('.grid'),
    cloneElementClassName: 'clone-grid-item'
});

Demo：jsdemo.codeman.top/html/dragga…

为何不使用HTML拖放API实现？

因为原生HTML拖放API在移动端无法使用，所以为了兼容PC端和移动端，使用了PointerEvent事件实现拖拽逻辑。

写在最后

至此，拖拽排序的基本功能已经实现，但还存在很多不足。像嵌套拖拽，跨列表拖拽，拖拽到底部自动滚动等功能都未实现。有兴趣的小伙伴可参考开源库自行研究。

多说一句（更新于2021-11-17 10:28）

我又根据angular cdk的拖拽排序写了个demo，具体实现方式大同小异。小伙伴们可自行体验，找找不同。

Demo：jsdemo.codeman.top/html/dragAn…