HTML Drag and Drop interfaces enable web applications to drag and drop files on a web page. This document describes how an application can accept one or more files that are dragged from the underlying platform's file manager and dropped on a web page.
The main steps to drag and drop are to define a
drop zone
(i.e. a target element for the file drop) and to define event handlers for the
drop
and
dragover
events. These steps are described below, including example code snippets. The full source code is available in
MDN's drag-and-drop repository
(pull requests and/or issues are welcome).
注意：
HTML drag and drop
defines two different APIs to support dragging and dropping files. One API is the
DataTransfer
interface and the second API is the
DataTransferItem
and
DataTransferItemList
interfaces. This example illustrates the use of both APIs (and does not use any Gecko specific interfaces).
target element
的
drop
event needs an
ondrop
global event handler. The following code snippet shows how this is done with a
<div>
元素：
<div id="drop_zone" ondrop="dropHandler(event);"> <p>Drag one or more files to this Drop Zone ...</p> </div>
Typically, an application will include a
dragover
event handler on the drop target element and that handler will turn off the browser's default drag behavior. To add this handler, you need to include a
ondragover
global event handler:
<div id="drop_zone" ondrop="dropHandler(event);" ondragover="dragOverHandler(event);"> <p>Drag one or more files to this Drop Zone ...</p> </div>
Lastly, an application may want to style the drop target element to visually indicate the element is a drop zone. In this example, the drop target element uses the following styling:
#drop_zone {
border: 5px solid blue;
width: 200px;
height: 100px;
}
注意，
dragstart
and
dragend
events are not fired when dragging a file into the browser from the OS.
drop
event is fired when the user drops the file(s). In the following drop handler, if the browser supports
DataTransferItemList
interface, the
getAsFile()
method is used to access each file; otherwise the
DataTransfer
接口的
文件
property is used to access each file.
This example shows how to write the name of each dragged file to the console. In a
real
application, an application may want to process a file using the
文件 API
.
Note that in this example, any drag item that is not a file is ignored.
function dropHandler(ev) {
console.log('File(s) dropped');
// Prevent default behavior (Prevent file from being opened)
ev.preventDefault();
if (ev.dataTransfer.items) {
// Use DataTransferItemList interface to access the file(s)
for (var i = 0; i < ev.dataTransfer.items.length; i++) {
// If dropped items aren't files, reject them
if (ev.dataTransfer.items[i].kind === 'file') {
var file = ev.dataTransfer.items[i].getAsFile();
console.log('... file[' + i + '].name = ' + file.name);
}
}
} else {
// Use DataTransfer interface to access the file(s)
for (var i = 0; i < ev.dataTransfer.files.length; i++) {
console.log('... file[' + i + '].name = ' + ev.dataTransfer.files[i].name);
}
}
}
下列
dragover
event handler calls
preventDefault()
to turn off the browser's default drag and drop handler.
function dragOverHandler(ev) {
console.log('File(s) in drop zone');
// Prevent default behavior (Prevent file from being opened)
ev.preventDefault();
}