JS实现图片拖拽交换效果

JS实现图片拖拽交换效果，供大家参考，具体内容如下

听 WEB前端javascript企业实战班 公开课，用JS实现了图片拖拽交换的目的；感谢老师的讲解。

实现要点

• 鼠标点击onmousedown：获取鼠标在页面上可视区域的位置(clientX, clientY)和元素外边框距已定位父元素容器的位置(offsetLeft,offsetTop)；
• 鼠标移动onmousemove: 获取鼠标在页面上可视区域的位置(clientX, clientY),并实时改变目标元素位置；进行碰撞检测，同时计算被碰撞元素与目标元素中心点距离，将距离最小的定位交换元素；
• 鼠标释放onmouseup: 进行元素交换
  

注意点

• 排除没有碰撞成功的情况，进行特殊讨论；
• 覆盖html5原有的图片拖拽功能，通过return false返回；
• 交换时同时勿忘记交换图片的索引；
  

小技巧

• 进行碰撞检测时，可以进行逆向思维，检测未碰撞的情况，即判断目标元素是否超过碰撞元素的边界(如：目标元素的右侧是否超过被碰撞元素的左侧)
• 计算元素中心位置时，可以改为计算元素左上角之间的距离，从而转变为计算(offsetLeft1,offsetTop1)(offsetLeft1,offsetTop1)与(offsetLefti(offsetLefti, offsetTopi)offsetTopi)的距离,以简化计算；
  

实现

HTML

CSS

* {
      margin:0;
      padding: 0;
    }
    body {
      user-select: none;  
    }
    #photo {
      width: 600px;
      height: 600px;
      border: 2px solid #000;
      margin: 20px auto;
    }
    #photo ul li {
      list-style:none;
      width: 180px;
      height: 180px;
      margin: 10px;
      float: left;
    }
    #photo ul li:hover {
      background: #c0c;
    }
    #photo ul li img {
      width: 180px;
      height: 180px;
      border: 1px solid #ccc;
    }

JS

var photo = document.getElementById("photo");
    var oUl = photo.getElementsByTagName("ul")[0];
    var aLi = oUl.getElementsByTagName("li");
    var z = 2;

    var arr = [];
    for (var i = 0; i < aLi.length; i++) {
      arr.push([aLi[i].offsetLeft, aLi[i].offsetTop]);
    }

    for (var i = 0; i < aLi.length; i++) {
      aLi[i].style.position = "absolute";
      aLi[i].style.left = arr[i][0] + "px";
      aLi[i].style.top = arr[i][1] + "px";
      aLi[i].style.margin = 0;
    }

    for (var i = 0; i < aLi.length; i++) {
      aLi[i].index = i;
      drag(aLi[i]);
    }

    function drag(obj) {
      obj.onmousedown = function(ev) {
 ev = ev || window.ev;
 var x = ev.clientX;
 var y = ev.clientY;

 var l = obj.offsetLeft;
 var t = obj.offsetTop;

 this.style.zIndex = z++;

 document.onmousemove = function(ev) {
   ev = ev || window.ev;
   var _left = ev.clientX - x + l;
   var _top = ev.clientY - y + t;
   obj.style.left = _left + "px";
   obj.style.top = _top + "px";

   var li = near(obj);
   for (var i = 0; i < aLi.length; i++) {
     aLi[i].style.background = "";
   }
   if (li) {
     li.style.background = "#DF971F";
   }
 }
 document.onmouseup = function() {
   document.onmousemove = null;
   document.onmousedown = null;

   var nearLi = near(obj);
   var tmp = 0;
   if (nearLi) {
     move(nearLi, {left:arr[obj.index][0], top:arr[obj.index][1]});
     move(obj, {left:arr[nearLi.index][0], top:arr[nearLi.index][1]});
     nearLi.style.background = "";

     tmp = obj.index;
     obj.index = nearLi.index;
     nearLi.index = tmp;
   } else {
     move(obj, {left:arr[obj.index][0], top:arr[obj.index][1]});
   }
 }
 return false;
      }
    } 
    function impact(obj1, obj2) {
      var L1 = obj1.offsetLeft;
      var R1 = obj1.offsetLeft + obj1.offsetWidth;
      var T1 = obj1.offsetTop;
      var B1 = obj1.offsetTop + obj1.offsetHeight;

      var L2 = obj2.offsetLeft;
      var R2 = obj2.offsetLeft + obj2.offsetWidth;
      var T2 = obj2.offsetTop;
      var B2 = obj2.offsetTop + obj2.offsetHeight;

      if (L2 > R1 || T2 > B1 || R2 < L1 || B2 < T1) {
 return false;
      } else {
 return true;
      }
    }
    function near(obj) {
      var tmp = 5000;
      var oLi = '';
      for (var i = 0; i < aLi.length; i++) {
 if (impact(obj, aLi[i]) && obj != aLi[i]) {
   var c = disCalc(obj, aLi[i]);

   if (tmp > c) {
     tmp = c;
     oLi = aLi[i];
   }
 }
      }
      return oLi;
    }
    function disCalc(obj1, obj2) {
      var x = obj1.offsetLeft - obj2.offsetLeft; 
      var y = obj1.offsetTop - obj2.offsetTop;
      return Math.sqrt(x * x + y * y);
    }

move.js

function move(obj, json, endFn) {
  clearInterval(obj.timer);
  obj.timer = setInterval(function() {
    var bBtn = true;
    for (var attr in json) {
      var iCur = 0;
      if (attr == 'opacity') {
 if (Math.round(parseFloat(getStyle(obj,attr)) * 100) == 0) {
   iCur = Math.round(parseFloat(getStyle(obj,attr)) * 100);
 } else {
   iCur = Math.round(parseFloat(getStyle(obj,attr)) * 100) || 100;
 }  
      } else {
 iCur = parseInt(getStyle(obj,attr)) || 0;
      }

      var iSpeed = (json[attr] - iCur) / 8;
      iSpeed = iSpeed >0 ? Math.ceil(iSpeed) : Math.floor(iSpeed);
      if (iCur != json[attr]) {
 bBtn = false;
      }

      if (attr == 'opacity') {
 obj.style.filter = 'alpha(opacity=' +(iCur + iSpeed)+ ')';
 obj.style.opacity = (iCur + iSpeed) / 100;
      }
      else {
 obj.style[attr] = iCur + iSpeed + 'px';
      }
    }

    if (bBtn) {
      clearInterval(obj.timer);
      if (endFn) {
 endFn.call(obj);
      }
    }  
  }, 30);
}


function getStyle(obj, attr) { 
  if (obj.currentStyle) {
    return obj.currentStyle[attr];
  } else {
    return getComputedStyle(obj, false)[attr];
  }
}

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