如何使用 JavaScript 从头开始​​实现拖放 div？

Question

它应该是 CSS 和 JavaScript 的组合。要做的步骤应该是：

1. 将其置于所有其他元素之上（指定哪个属性？）
2. 点击事件时捕捉事件（监听哪个事件？）
3. 在鼠标移动时移动 div。

但是细节是什么？

Answer 1

jQuery 方式：

查看jQueryUI 插件draggable 和droppable。

已经在 jQuery 框架上投入了数百个小时，以使此类复杂的任务变得微不足道。利用 jQuery 团队的努力，让我们所有人更轻松地编写丰富的跨浏览器应用程序；)

查克·诺里斯的方式：

如果您坚持使用原始 javascript 进行尝试。你会想做一些事情。一，以编程方式将所有可拖动项目设置为相对/绝对定位。如果单击特定项目，请使其在 CSS 中的顶部/左侧值反映鼠标 x、y 轴所做的更改，直到释放单击为止。此外，您需要更新每个可拖动对象的 z-index，当它被单击以将其显示在视图中时。

教程：How to Drag and Drop with Javascript

Answer 2

1. 使其绝对定位，具有高 z-index。
2. 检查 div 的 onmousedown。
3. 使用事件的 mouseX 和 mouseY 属性来移动 div。

这是来自Javascript, the Definitive Guide 的示例（已更新here）：

/**
 *  Drag.js:    drag absolutely positioned HTML elements.
 *
 *  This module defines a single drag() function that is designed to be called
 *  from an onmousedown event handler. Subsequent mousemove event will
 *  move the specified element. A mouseup event will terminate the drag.
 *  If the element is dragged off the screen, the window does not scroll.
 *  This implementation works with both the DOM Level 2 event model and the
 *  IE event model.
 *
 *  Arguments:
 *
 *      elementToDrag: the element that received the mousedown event or
 *          some containing element. It must be absolutely positioned. Its
 *          style.left and style.top values will be changed based on the user's
 *          drag.
 *
 *      event: ethe Event object for the mousedown event.
 *
 *  Example of how this can be used:
 *      <script src="Drag.js"></script> <!-- Include the Drag.js script -->
 *      <!-- Define the element to be dragged -->
 *      <div style="postion:absolute; left:100px; top:100px; width:250px;
 *                  background-color: white; border: solid black;">
 *      <!-- Define the "handler" to drag it with. Note the onmousedown attribute. -->
 *      <div style="background-color: gray; border-bottom: dotted black;
 *                  padding: 3px; font-family: sans-serif; font-weight: bold;"
 *          onmousedown="drag(this.parentNode, event);">
 *      Drag Me <!-- The content of the "titlebar" -->
 *      </div>
 *      <!-- Content of the draggable element -->
 *      <p>This is a test. Testing, testing, testing.<p>This is a test.<p>Test.
 *      </div>
 *
 *  Author: David Flanagan; Javascript: The Definitive Guide (O'Reilly)
 *  Page: 422
 **/
 function drag(elementToDrag, event)
 {
     // The mouse position (in window coordinates)
     // at which the drag begins
     var startX = event.clientX, startY = event.clientY;

     // The original position (in document coordinates) of the
     // element that is going to be dragged. Since elementToDrag is
     // absolutely positioned, we assume that its offsetParent is the
     //document bodt.
     var origX = elementToDrag.offsetLeft , origY = elementToDrag.offsetTop;

     // Even though the coordinates are computed in different
     // coordinate systems, we can still compute the difference between them
     // and use it in the moveHandler() function. This works because
     // the scrollbar positoin never changes during the drag.
     var deltaX = startX - origX, deltaY = startY - origY;

     // Register the event handlers that will respond to the mousemove events
     // and the mouseup event that follow this mousedown event.
     if (document.addEventListener) //DOM Level 2 event model
     {
         // Register capturing event handlers
         document.addEventListener("mousemove", moveHandler, true);
         document.addEventListener("mouseup", upHandler, true);
     }
     else if (document.attachEvent) //IE 5+ Event Model
     {
         //In the IE event model, we capture events by calling
         //setCapture() on the element to capture them.
         elementToDrag.setCapture();
         elementToDrag.attachEvent("onmousemove", moveHandler);
         elementToDrag.attachEvent("onmouseup", upHandler);
         // Treat loss of mouse capture as a mouseup event.
         elementToDrag.attachEvent("onclosecapture", upHandler);
     }
     else //IE 4 Event Model
     {
         // In IE 4, we can't use attachEvent() or setCapture(), so we set
         // event handlers directly on the document object and hope that the
         // mouse event we need will bubble up.
         var oldmovehandler = document.onmousemove; //used by upHandler()
         var olduphandler = document.onmouseup;
         document.onmousemove = moveHandler;
         document.onmouseup = upHandler;
     }

     // We've handled this event. Don't let anybody else see it.
     if (event.stopPropagation) event.stopPropagation();    //  DOM Level 2
     else event.cancelBubble = true;                        //  IE

     // Now prevent any default action.
     if (event.preventDefault) event.preventDefault();      //  DOM Level 2
     else event.returnValue = false;                        //  IE

     /**
      * This is the handler that captures mousemove events when an element
      * is being dragged. It is responsible for moving the element.
      **/
      function moveHandler(e)
      {
          if (!e) e = window.event; //  IE Event Model

          // Move the element to the current mouse position, adjusted as
          // necessary by the offset of the initial mouse-click.
          elementToDrag.style.left = (e.clientX - deltaX) + "px";
          elementToDrag.style.top = (e.clientY - deltaY) + "px";

          // And don't let anyone else see this event.
          if (e.stopPropagation) e.stopPropagation();       // DOM Level 2
          else e.cancelBubble = true;                       // IE
      }

      /**
       * This is the handler that captures the final mouseup event that
       * occurs at the end of a drag.
       **/
       function upHandler(e)
       {
           if (!e) e = window.event;    //IE Event Model

           // Unregister the capturing event handlers.
           if (document.removeEventListener) // DOM event model
            {
                document.removeEventListener("mouseup", upHandler, true);
                document.removeEventListener("mousemove", moveHandler, true);
            }
            else if (document.detachEvent)  //  IE 5+ Event Model
            {
                elementToDrag.detachEvent("onlosecapture", upHandler);
                elementToDrag.detachEvent("onmouseup", upHandler);
                elementToDrag.detachEvent("onmousemove", moveHandler);
                elementToDrag.releaseCapture();
            }
            else    //IE 4 Event Model
            {
                //Restore the original handlers, if any
                document.onmouseup = olduphandler;
                document.onmousemove = oldmovehandler;
            }

            //  And don't let the event propagate any further.
            if (e.stopPropagation) e.stopPropagation(); //DOM Level 2
            else e.cancelBubble = true;                 //IE
       }
 }

 function closeMe(elementToClose)
 {
     elementToClose.innerHTML = '';
     elementToClose.style.display = 'none';
 }

 function minimizeMe(elementToMin, maxElement)
 {
     elementToMin.style.display = 'none';
 }

Answer 3

HTML5 拖放

如果您在 2017 年或之后阅读本文，您可能想看看 HTML5 Drag and Drop API：

https://developer.mozilla.org/docs/Web/API/HTML_Drag_and_Drop_API

例子：

<!DOCTYPE HTML>
<html>
<head>
    <script>
    function allowDrop(ev) {
        ev.preventDefault();
    }

    function drag(ev) {
        ev.dataTransfer.setData("text", ev.target.id);
    }

    function drop(ev) {
        ev.preventDefault();
        var data = ev.dataTransfer.getData("text");
        ev.target.appendChild(document.getElementById(data));
    }
    </script>
    <style>
        .draggable {
            border: 1px solid black;
            width: 30px;
            height: 20px;
            float: left;
            margin-right: 5px;
        }
        #target {
            border: 1px solid black;
            width: 150px;
            height: 100px;
            padding: 5px;
        }
    </style>
</head>
<body>

    <h1>Drag and Drop</h1>

    <h2>Target</h2>
    <div id="target" ondrop="drop(event)" ondragover="allowDrop(event)"></div>

    <h2>Draggable Elements</h2>
    <div id="draggable1" class="draggable" draggable="true" ondragstart="drag(event)"></div>
    <div id="draggable2" class="draggable" draggable="true" ondragstart="drag(event)"></div>
    <div id="draggable3" class="draggable" draggable="true" ondragstart="drag(event)"></div>

</body>
</html>

Answer 4

function allowDrop(ev) {
    ev.preventDefault();
}

function drag(ev) {
    ev.dataTransfer.setData("text", ev.target.id);
}

function drop(ev) {
    ev.preventDefault();
    var data = ev.dataTransfer.getData("text");
    ev.target.appendChild(document.getElementById(data));
}

.mydiv {
    float: left;
    width: 100px;
    height: 35px;
    margin: 10px;
    padding: 10px;
    border: 1px solid black;
}

<!DOCTYPE HTML>
<html>
<head>


</head>
<body>

<h2>Drag and Drop</h2>


<div id="div1" class="mydiv" ondrop="drop(event)" ondragover="allowDrop(event)">
  <img src="https://cdn.sstatic.net/Sites/stackoverflow/company/img/logos/so/so-logo.png?v=9c558ec15d8a" draggable="true" ondragstart="drag(event)" id="drag1" width="88" height="31">
</div>

<div id="div2" class="mydiv" ondrop="drop(event)" ondragover="allowDrop(event)"></div>
<div id="div3" class="mydiv" ondrop="drop(event)" ondragover="allowDrop(event)"></div>
<div id="div4" class="mydiv" ondrop="drop(event)" ondragover="allowDrop(event)"></div>

</body>
</html>

Answer 5

标准的拖放 API 被 suck big hairy donkey balls 广泛认可。所以我不建议从头开始做。但既然这是你的问题，那么制作可拖动的东西有一组要求，以及正确设置拖放区的一组要求：

拖动：

• dom 节点必须将“可拖动”属性设置为 true

注意：e.dataTransfer.setDragImage可用于设置备用拖动图片（默认为被拖动dom节点的透明图片。

注意2：e.dataTransfer.setData可以在dragstart事件中使用，设置一些可以从drop事件中取回的数据。

掉落：

• 在dragover 事件中，必须调用e.preventDefault
• 在drop 事件中，必须调用e.preventDefault

例子：

<body>
    <div id="dragme" draggable="true">Drag Me</div>
    <div id="dropzone">Drop Here</div>
</body>

<script>
    var dragme = document.getElementById('dragme')
    var dropzone = document.getElementById('dropzone')

    dragme.addEventListener('dragstart',function(e){
        dropzone.innerHTML = "drop here"
    })

    dropzone.addEventListener('dragover',function(e){
        e.preventDefault()
    })
    dropzone.addEventListener('drop',function(e){
        e.preventDefault()
        dropzone.innerHTML = "dropped"
    })
</script>

但是，使用这个 API 有很多陷阱，包括：

• 要区分拖放区上的 dragmove 事件和与可拖动项目相关的 dragmove 事件需要做很多工作
• dragmove 即使你的鼠标没有移动也会触发
• dragleave 和 dragenter 即使您的鼠标没有移入或移出侦听 dom 节点也会触发（由于某些愚蠢的原因，它会在越过父子边界时触发）
• 还有更多..

更好的方法

我编写了一个拖放库，它使使用标准拖放 API 变得更加容易，而没有所有这些陷阱。在这里查看：

https://github.com/fresheneesz/drip-drop

Answer 6

是的，如果你想要一个拥有比你需要的更多功能的臃肿库，你可以使用 jQuery！或者，如果您想成为更多精英，请使用 Waltern Zorn's drag and drop library，它的大小只有十分之一。

Answer 7

1. 要将 div 置于其他元素之上，您必须为其指定高 z-index。此外，您可以设置 box-shadow 以向用户反馈该元素是可拖动的。
2. 您总共需要监听三个事件：mousedown、mouseup 和 鼠标移动。在 mousedown 上，您必须在 mousemove 上附加一个监听器，它会跟踪鼠标指针的移动并相应地移动 div ，并且在 mouseup 上，您必须删除 mousemove 上的侦听器。
3. 用鼠标移动 div 有点棘手。如果您翻译 div 到指针的位置，指针将始终指向 div 的左上角，即使您单击右下角也是如此。为此，您必须在 mousedown 事件处理程序中计算 div（左上角）和鼠标指针之间的坐标差。然后，您必须在 mousemove 事件处理程序中将 div 转换到该位置之前从鼠标位置减去该差异。

See the demo for a better idea.

<!DOCTYPE html>
<html lang="en">
  <head>
    <meta charset="UTF-8" />
    <meta name="viewport" content="width=device-width, initial-scale=1.0" />
    <meta http-equiv="X-UA-Compatible" content="ie=edge" />
    <title>Document</title>
    <style>
      body,
      html {
        width: 100%;
        height: 100%;
        padding: 0px;
        margin: 0px;
      }
      #box {
        width: 100px;
        height: 100px;
        margin: auto;
        background-color: lightblue;
      }
      #box:active {
        border: 1px solid black;
        box-shadow: 2px 2px 5px 5px #bbb6b6;
      }
    </style>
  </head>
  <body>
    <div id="box"></div>
  </body>
  <script>
    var box = document.getElementById("box");
    var diff = {};
    var getBoxPos = function() {
      return {
        x: box.getBoundingClientRect().x,
        y: box.getBoundingClientRect().y
      };
    };
    var calcDiff = function(x, y) {
      var boxPos = getBoxPos();
      diff = {
        x: x - boxPos.x,
        y: y - boxPos.y
      };
    };
    var handleMouseMove = function(event) {
      var x = event.x;
      var y = event.y;
      x -= diff.x;
      y -= diff.y;

      console.log("X " + x + " Y " + y);
      box.style.position = "absolute";
      box.style.transform = "translate(" + x + "px ," + y + "px)";
    };

    box.addEventListener("mousedown", function(e) {
      calcDiff(e.x, e.y);
      box.addEventListener("mousemove", handleMouseMove, true);
    });

    box.addEventListener("mouseup", function(e) {
      console.log("onmouseup");
      box.removeEventListener("mousemove", handleMouseMove, true);
    });
  </script>
</html>

Answer 8

您可以使用以下代码来做到这一点

$(function() { 
        $("#imageListId").sortable({ 
            update: function(event, ui) { 
                    getIdsOfImages(); 
                } //end update          
        }); 
    }); 
  
    function getIdsOfImages() { 
        var values = []; 
        $('.listitemClass').each(function(index) { 
            values.push($(this).attr("id") 
                        .replace("imageNo", "")); 
        }); 
        $('#outputvalues').val(values); 
    }

/* text align for the body */
    body { 
        text-align: center; 
    } 
      
    /* image dimension */
    img { 
        height: 200px; 
        width: 350px; 
    } 
      
    /* imagelistId styling */
    #imageListId { 
        margin: 0; 
        padding: 0; 
        list-style-type: none; 
    } 
       
    #imageListId div { 
        margin: 0 4px 4px 4px; 
        padding: 0.4em; 
        display: inline-block; 
    } 
      
    /* Output order styling */
    #outputvalues { 
        margin: 0 2px 2px 2px; 
        padding: 0.4em; 
        padding-left: 1.5em; 
        width: 250px; 
        border: 2px solid dark-green; 
        background: gray; 
    } 
       
    .listitemClass { 
        border: 1px solid #006400; 
        width: 350px; 
    } 
       
    .height { 
        height: 10px; 
    }

<link href="https://code.jquery.com/ui/1.10.4/themes/ui-lightness/jquery-ui.css" rel="stylesheet"/>
<script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/1.10.2/jquery.min.js"></script>
<script src="https://code.jquery.com/ui/1.10.4/jquery-ui.js"></script>

<!DOCTYPE html> 
<html> 
<head> 
    <title> 
        Drag Drop feature
    </title> 
</head> 
       
<body> 
    <h1 style="color:green">GeeksforGeeks</h1>  
      
    <b>Drag and drop using jQuery UI Sortable</b> 
      
    <div class="height"></div><br> 
      
    <div id = "imageListId"> 
        <div id="imageNo1" class = "listitemClass"> 
            <img src="images/geeksimage1.png" alt=""> 
        </div> 
          
        <div id="imageNo2" class = "listitemClass"> 
            <img src="images/geeksimage2.png" alt=""> 
        </div> 
          
        <div id="imageNo3" class = "listitemClass"> 
            <img src="images/geeksimage3.png" alt=""> 
        </div> 
          
        <div id="imageNo4" class = "listitemClass"> 
            <img src="images/geeksimage4.png" alt=""> 
        </div> 
          
        <div id="imageNo5" class = "listitemClass"> 
            <img src="images/geeksimage5.png" alt=""> 
        </div> 
          
        <div id="imageNo6" class = "listitemClass"> 
            <img src="images/geeksimage6.png" alt=""> 
        </div> 
    </div> 
      
    <div id="outputDiv"> 
        <b>Output of ID's of images : </b> 
        <input id="outputvalues" type="text" value="" /> 
    </div> 
</body> 
  
</html>