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Implementation code of HTML5 drag and drop effect

黄舟Original: 2017-02-21 13:11:201396browse

Drag and drop

Drag and drop is a common feature where you grab an object and then drag it to another location.

In HTML5, drag and drop is part of the standard, and any element can be dragged and dropped.

Internet Explorer 9+, Firefox, Opera, Chrome, and Safari support dragging.

Note:Safari 5.1.2 does not support dragging.

Example:

<!DOCTYPE html>  
<html>  
<head>  
    <title>拖放</title>  
    <style type="text/css">  
        #p1{width:360px;height:220px;padding:20px;border:1px solid black;}  
    </style>  
    <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>  
</head>  
<body>  
    <p id="p1" ondrop="drop(event)" ondragover="allowDrop(event)"></p>  
    <br />  
    <img id="drag1" src="img/bg_1.jpg" draggable="true" ondragstart="drag(event)"  width="300px" height="180px" />  
</body>  
</html>

First, in order to make the element draggable, set the draggable attribute to true: 543de1d7dc5f045a59906d8e77ab7ed0

Then, specify that when the element is dragged, what will happen What.
In the above example, ondragstart attribute calls a function, drag(event), which specifies the data to be dragged.
dataTransfer.setData() method Set the data type and value of the dragged data:

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

In this example, data The type is "Text" and the value is the id of the draggable element ("drag1").

ondragover event Specifies where to place the dragged data.
By default, data/elements cannot be placed into other elements. If we need to allow placement, we must prevent the default handling of the element.
This is done by calling the event.preventDefault() method of ondragover event : event.preventDefault()

When the dragged data is placed, a drop will occur event.
In the above example, the ondrop attribute calls a function, drop(event):

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

Code explanation:

Call preventDefault() to avoid the browser's default processing of data (the default behavior of the drop event is to open it as a link)
Through dataTransfer.getData("Text" ) MethodGet the dragged data. This method will return any data set to the same type in the setData() method.
The dragged data is the id of the dragged element ("drag1")
Append the dragged element to the placed element (target element)

Drag back and forth:

If you want to drag back and forth between two places, just slightly modify the above code.
Change the code in the body to:

<body>  
    <p id="p1" ondrop="drop(event)" ondragover="allowDrop(event)">  
    <img id="drag1" src="img/bg_1.jpg" draggable="true" ondragstart="drag(event)"  width="300px" height="180px" /></p>  
    <p id="p2" ondrop="drop(event)" ondragover="allowDrop(event)"></p>  
</body>

Then add #p2 to the style:

<style type="text/css">  
        #p1,#p2{width:360px;height:220px;padding:20px;border:1px solid black;}  
    </style>

This way you can drag and drop back and forth.

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