DataTransfer.clearData()
DataTransfer.clearData()
方法删除给定类型的拖动操作的 drag data
。如果给定类型的数据不存在,则此方法不执行任何操作。
如果调用此方法时没有传入参数,或者参数为空字符串
,则将删除所有类型的数据。
此方法不会从拖动操作中删除文件,因此如果有任何文件包含在对象的 DataTransfer.types
列表中,仍然可能有一个类型为“Files”的条目在拖动。
备注:该方法只能在 dragstart
事件的处理程序中使用,因为这是拖动操作的数据存储唯一能写入的时间。
语法
js
DataTransfer.clearData([format]);
参数
示例
这个例子显示了使用 DataTransfer
对象的 getData()
、setData()
以及 clearData()
方法。
HTML
html
<span class="tweaked" id="source" draggable="true">
Select this element, drag it to the Drop Zone and then release the selection
to move the element.
</span>
<span class="tweaked" id="target">Drop Zone</span>
<div>Status: <span id="status">Drag to start</span></div>
<div>Data is: <span id="data">uninitialized</span></div>
CSS
css
span.tweaked {
display: inline-block;
margin: 1em 0;
padding: 1em 2em;
}
#source {
color: blue;
border: 1px solid black;
}
#target {
border: 1px solid black;
}
JavaScript
js
window.addEventListener("DOMContentLoaded", function () {
// Select HTML elements
var draggable = document.getElementById("source");
var dropable = document.getElementById("target");
var status = document.getElementById("status");
var data = document.getElementById("data");
var dropped = false;
// Register event handlers
draggable.addEventListener("dragstart", dragStartHandler);
draggable.addEventListener("dragend", dragEndHandler);
dropable.addEventListener("dragover", dragOverHandler);
dropable.addEventListener("dragleave", dragLeaveHandler);
dropable.addEventListener("drop", dropHandler);
function dragStartHandler(event) {
status.textContent = "Drag in process";
// Change target element's border to signify drag has started
event.currentTarget.style.border = "1px dashed blue";
// Start by clearing existing clipboards; this will affect all types since we
// don't give a specific type.
event.dataTransfer.clearData();
// Set the drag's format and data (use event target's id for data)
event.dataTransfer.setData("text/plain", event.target.id);
data.textContent = event.dataTransfer.getData("text/plain");
}
function dragEndHandler(event) {
if (!dropped) {
status.textContent = "Drag canceled";
}
data.textContent = event.dataTransfer.getData("text/plain") || "empty";
// Change border to signify drag is no longer in process
event.currentTarget.style.border = "1px solid black";
if (dropped) {
// Remove all event listeners
draggable.removeEventListener("dragstart", dragStartHandler);
draggable.removeEventListener("dragend", dragEndHandler);
dropable.removeEventListener("dragover", dragOverHandler);
dropable.removeEventListener("dragleave", dragLeaveHandler);
dropable.removeEventListener("drop", dropHandler);
}
}
function dragOverHandler(event) {
status.textContent = "Drop available";
event.preventDefault();
}
function dragLeaveHandler(event) {
status.textContent = "Drag in process (drop was available)";
event.preventDefault();
}
function dropHandler(event) {
dropped = true;
status.textContent = "Drop done";
event.preventDefault();
// Get data linked to event format « text »
var _data = event.dataTransfer.getData("text/plain");
var element = document.getElementById(_data);
// Append drag source element to event's target element
event.target.appendChild(element);
// Change CSS styles and displayed text
element.style.cssText =
"border: 1px solid black;display: block; color: red";
element.textContent = "I'm in the Drop Zone!";
}
});
规范
Specification |
---|
HTML Standard # dom-datatransfer-cleardata-dev |
浏览器兼容性
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