每天一课：HTML5拖放实例(附源代码)_html/css

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每天一课：HTML5拖放实例(附源代码)_html/css_WEB-ITnose

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Jun 24, 2016 am 11:16 AM

拖放（Drag和drop）是HTML5标准的组成部分。

拖放

拖放是一种常见的特性，即抓取对象以后拖到另一个位置。

在HTML5中，拖放是标准的一部分，任何元素都能够拖放。

浏览器支持

Internet Explorer 9、Firefox、Opera 12、Chrome以及Safari5支持拖放（注：在Safari5.1.2中不支持）

HTML5 拖放实例

下面的例子是一个简单的拖放实例：

实例

<!DOCTYPE HTML><html><head><script type="text/javascript">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></head><body><div id="div1" ondrop="drop(event)"ondragover="allowDrop(event)"></div><img  src="/static/imghwm/default1.png"  data-src="img_logo.gif"  class="lazy"  id="drag1" draggable="true"ondragstart="drag(event)"    style="max-width:90%"  style="max-width:90%" / alt="每天一课：HTML5拖放实例(附源代码)_html/css_WEB-ITnose" ></body></html>

它看上去也许有些复杂，不过我们可以分别研究拖放事件的不同部分。

设置元素为可拖放

首先，为了使元素可拖动，把 draggable 属性设置为 true ：

<img  draggable="true" / alt="每天一课：HTML5拖放实例(附源代码)_html/css_WEB-ITnose" >

拖动什么 - ondragstart 和 setData()

然后，规定当元素被拖动时，会发生什么。

在上面的例子中，ondragstart 属性调用了一个函数，drag(event)，它规定了被拖动的数据。

dataTransfer.setData() 方法设置被拖数据的数据类型和值：

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

在这个例子中，数据类型是 "Text"，值是可拖动元素的 id ("drag1")。

放到何处 - ondragover

ondragover 事件规定在何处放置被拖动的数据。

默认地，无法将数据/元素放置到其他元素中。如果需要设置允许放置，我们必须阻止对元素的默认处理方式。

这要通过调用 ondragover 事件的 event.preventDefault() 方法：

event.preventDefault()

进行放置 - ondrop

当放置被拖数据时，会发生 drop 事件。

在上面的例子中，ondrop 属性调用了一个函数，drop(event)：

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

代码解释：

调用 preventDefault() 来避免浏览器对数据的默认处理（drop 事件的默认行为是以链接形式打开）
通过 dataTransfer.getData("Text") 方法获得被拖的数据。该方法将返回在 setData() 方法中设置为相同类型的任何数据。
被拖数据是被拖元素的 id ("drag1")
把被拖元素追加到放置元素（目标元素）中

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