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+---
+title: DataTransferItemList.length
+slug: Web/API/DataTransferItemList/length
+translation_of: Web/API/DataTransferItemList/length
+---
+<p>{{domxref("DataTransferItemList")}} 接口的只读属性<code><strong>length</strong></code> 返回当前拖动项列表中项目的数量.</p>
+
+<h2 id="Syntax" name="Syntax">语法</h2>
+
+<pre class="syntaxbox"><em>length</em> = <em>DataTransferItemList</em>.length;
+</pre>
+
+<h3 id="Return_Value" name="Return_Value">值</h3>
+
+<p>列表中拖动项的数量,如果列表为空或禁用则为0。如果列表的{{domxref("DataTransfer")}}对象未与拖动数据存储关联,则认为拖动列表被禁用。</p>
+
+<h2 id="Example_Drag_and_Drop" name="Example_Drag_and_Drop">示例</h2>
+
+<p>这个例子演示了<code>length</code> 属性的用法。</p>
+
+<h3 id="JavaScript">JavaScript</h3>
+
+<pre class="brush: js">function dragstart_handler(ev) {
+ console.log("dragStart");
+ // Add this element's id to the drag payload so the drop handler will
+ // know which element to add to its tree
+ var dataList = ev.dataTransfer.items;
+ dataList.add(ev.target.id, "text/plain");
+ // Add some other items to the drag payload
+ dataList.add("&lt;p&gt;... paragraph ...&lt;/p&gt;", "text/html");
+ dataList.add("http://www.example.org","text/uri-list");
+}
+
+function drop_handler(ev) {
+ console.log("Drop");
+ ev.preventDefault();
+ var data = ev.dataTransfer.items;
+ // Loop through the dropped items and log their data
+ for (var i = 0; i &lt; data.length; i++) {
+ if ((data[i].kind == 'string') &amp;&amp; (data[i].type.match('^text/plain'))) {
+ // This item is the target node
+ data[i].getAsString(function (s){
+ ev.target.appendChild(document.getElementById(s));
+ });
+ } else if ((data[i].kind == 'string') &amp;&amp; (data[i].type.match('^text/html'))) {
+ // Drag data item is HTML
+ data[i].getAsString(function (s){
+ console.log("... Drop: HTML = " + s);
+ });
+ } else if ((data[i].kind == 'string') &amp;&amp; (data[i].type.match('^text/uri-list'))) {
+ // Drag data item is URI
+ data[i].getAsString(function (s){
+ console.log("... Drop: URI = " + s);
+ });
+ }
+ }
+}
+
+function dragover_handler(ev) {
+ console.log("dragOver");
+ ev.preventDefault();
+ // Set the dropEffect to move
+ ev.dataTransfer.dropEffect = "move"
+}
+
+function dragend_handler(ev) {
+ console.log("dragEnd");
+ var dataList = ev.dataTransfer.items;
+ // Clear any remaining drag data
+ dataList.clear();
+}
+
+</pre>
+
+<h3 id="HTML">HTML</h3>
+
+<pre class="brush: html">&lt;div&gt;
+ &lt;p id="source" ondragstart="dragstart_handler(event);" ondragend="dragend_handler(event);" draggable="true"&gt;
+ Select this element, drag it to the Drop Zone and then release the selection to move the element.&lt;/p&gt;
+&lt;/div&gt;
+&lt;div id="target" ondrop="drop_handler(event);" ondragover="dragover_handler(event);"&gt;Drop Zone&lt;/div&gt;
+</pre>
+
+<h3 id="CSS">CSS</h3>
+
+<pre class="brush: css">div {
+ margin: 0em;
+ padding: 2em;
+}
+
+#source {
+ color: blue;
+ border: 1px solid black;
+}
+
+#target {
+ border: 1px solid black;
+}
+</pre>
+
+<h3 id="结果">结果</h3>
+
+<p>{{EmbedLiveSample('Example_Drag_and_Drop')}}</p>
+
+<p>{{LiveSampleLink('Example_Drag_and_Drop', 'Drag and Drop demo link')}}</p>
+
+<h2 id="规范">规范</h2>
+
+<table class="standard-table">
+ <tbody>
+ <tr>
+ <th scope="col">规范</th>
+ <th scope="col">状态</th>
+ <th scope="col">备注</th>
+ </tr>
+ <tr>
+ <td>{{SpecName('HTML WHATWG', 'interaction.html#dom-datatransferitemlist-length','length')}}</td>
+ <td>{{Spec2('HTML WHATWG')}}</td>
+ <td></td>
+ </tr>
+ <tr>
+ <td>{{SpecName('HTML5.1', 'editing.html#dom-datatransferitemlist-length','length')}}</td>
+ <td>{{Spec2('HTML5.1')}}</td>
+ <td>Not included in W3C HTML5 {{Spec2('HTML5 W3C')}}</td>
+ </tr>
+ <tr>
+ </tr>
+ </tbody>
+</table>
+
+<h2 id="Browser_compatibility">Browser compatibility</h2>
+
+
+
+<p>{{Compat("api.DataTransferItemList.length")}}</p>
+
+<div>{{APIRef("HTML Drag and Drop API")}}</div>