HTML에서 드래그 앤 드롭

다음 문서에서는 HTML의 드래그 앤 드롭에 대한 개요를 제공합니다. 드래그 앤 드롭은 편리한 기능 패턴으로 인해 웹 페이지에서 수동으로 입력을 제공하는 것으로 잘 알려진 최신 기능입니다. 드래그 앤 드롭 방식은 사용자가 소스 필드의 항목 목록에서 특정 데이터/옵션을 선택하고 이를 드래그하여 대상 필드에 드롭하는 과정으로 설명할 수 있습니다. 이는 HTML 웹 페이지의 여러 마우스 이벤트와 함께 문서 개체 모델을 사용하여 구현됩니다. 이 기능에 사용되는 다양한 이벤트로는 drag, dragstart, dragleave, dragenter, dragover, drop, dragend 및 dragexit가 있습니다.

드래그 앤 드롭 이벤트

최신 드래그 앤 드롭(dnd) 기능에는 여러 이벤트가 포함되어 있습니다. 다음과 같이 하나씩 살펴보겠습니다.

Sr. No	Events	Details Description
1	Drag	To drag entity(element or text) when the mouse is moved with the element to be dragged.
2	Dragstart	The very first step in drag and drop is dragstart. It gets executed when the user is going to start with dragging the object to the required location.
3	Dragenter	Dragenter event is used when the mouse is getting hover on the target element.
4	Dragleave	This event is used when the user releases a mouse from an element.
5	Dragover	This event occurs when a mouse is used to over an element.
6	Drop	This event is used at the end of the drag and drop process for drop element operation.
7	Dragend	This is one of the most important event in this process for releasing the mouse button from the element to complete the drag procedure.
8	Dragexit	This event status that the element is no longer in the drag process of urgent target selection of element.

Let’s see some data attributes on which Drag and drop operation going to happen:

• dataTransfer.dropEffect [ = value ]: This attribute is used to show which operation is currently going on. One can set it to replace the already selected operation. The values included in it like a copy, link, none or move.
• dataTransfer.effectAllowed [ = value ]: Whichever operations are allowed will be returned through this attribute. It’s also possible to set to changing an already selected operation.
• dataTransfer.files: This data attribute is used to get fileList of the files which are going to be dragged.
• dataTransfer.addElement(element): It’s used to insert the already existing element into a list of other elements that are useful to render the drag feedback.
• dataTransfer.setDragImage(element, x, y): This attribute is a little bit the same as above for updating drag feedback and help to change already existed feedback
• dataTransfer.clearData ( [ format ] ): It helps the user to remove data from the already defined format. If the user omitted the argument, the IT would remove all the data.
• dataTransfer.setData(format, data): It’s one of the popular attributes used to add specified data.
• data = dataTransfer.getData(format): This attribute in Drag and Drag operation is used to extract specified data. If there is no same data as it, it will return to the empty string.

Syntax of Drag and Drop in HTML

Here are a few steps defining the syntax for drag and drop:

Select the object to be a drag: Set attribute true to it.

<element draggable="true"></element>

Start dragging object:

function dragStart(ev){}

Drop the object:

function dragDrop(ev){}

Examples of Drag and Drop in HTML

The following example will show how exactly the drag and drop operation will perform in HTML.

Example #1

Code:

<title>Drag and Drop Demo</title>
<script>
function allowDrop(ev) {
ev.preventDefault();
}
function dragStart(ev) {
ev.dataTransfer.setData("text", ev.target.id);
}
function dragDrop(ev) {
ev.preventDefault();
var data = ev.dataTransfer.getData("text");
ev.target.appendChild(document.getElementById(data));
}
</script>
<style>
#box {
margin: auto;
width: 30%;
width: 21%;
height:150px;
border: 2px solid blue;
padding: 2px;
}
#square1, #square2, #square3 {
float: left;
margin: 5px;
padding: 10px;
}
#square1 {
width: 30px;
height: 30px;
background-color: #BEA7CC;
}
#square2 {
width: 60px;
height: 60px;
background-color: #B5D5F5;
}
#square3 {
width: 90px;
height: 90px;
background-color:#F5B5C5 ;
}
h2 {
font-size:20px;
font-weight:bold;
text-align:center;
}
</style>


<h2 id="HTML-DRAG-AND-DROP-DEMO">HTML DRAG AND DROP DEMO</h2>
<div id="box">
<div id="square1" draggable="true" ondragstart="dragStart(event)"></div>
<div id="square2" draggable="true" ondragstart="dragStart(event)"></div>
<div id="square3" ondrop="dragDrop(event)" ondragover="allowDrop(event)"></div>
</div>

Output:

Before drag and drop, option output will be as shown below:

After performing the Drag and Drop operation, the output will be as follows:

Example #2

Here we are going to see another example in which we will move the image from one location to another specified location as shown below code.

Code:

<script>
function allowDrop(ev) {
ev.preventDefault();
}
function dragStart(ev) {
ev.dataTransfer.setData("text", ev.target.id);
}
function dragDrop(ev) {
ev.preventDefault();
var data = ev.dataTransfer.getData("text");
ev.target.appendChild(document.getElementById(data));
}
</script>
<style>
.divfirst {
width: 250px;
height: 150px;
padding: 10px;
border: 1px solid black;
background-color: #F5F5F5;
}
p {
font-size:20px;
font-weight:bold;
}
</style>


<p>Image Drag and Drop Demo</p>
<div class="divfirst" ondrop="dragDrop(event)" ondragover="allowDrop(event)">
<img  src="/static/imghwm/default1.png" data-src="Jerry.jpeg" class="lazy" id="drag1" draggable="true" ondragstart="dragStart(event)"    style="max-width:90%"  style="max-width:90%" alt="HTML에서 드래그 앤 드롭" >
</div>
<br>
<div class="divfirst" ondrop="dragDrop(event)" ondragover="allowDrop(event)"></div>

Output:

Before drag and drop operation, the output is:

After the drag and drop operation is completed, it will look like this:

Example #3

In this example, we are going to see how to drag and drop file at the specified location:

Code:

<div id="filedemo" style="min-height: 150px; border: 1px solid black;" ondragenter="document.getElementById('output').textContent = ''; event.stopPropagation(); event.preventDefault();" ondragover="event.stopPropagation(); event.preventDefault();" ondrop="event.stopPropagation(); event.preventDefault();
dodrop(event);">
DROP FILES HERE...
</div>
<script>
function dodrop(event)
{
var dt = event.dataTransfer;
var files = dt.files;
for (var i = 0; i < files.length; i++) {
output(" File " + i + ":\n(" + (typeof files[i]) + ") : <" + files[i] + " > " +
files[i].name + " " );
}
}
function output(text)
{
document.getElementById("filedemo").textContent += text;
}
</script>

Output:

Conclusion

HTML drag and drop is one of the most important user interface entities that will use for different purposes like copying, deleting, or recording. It works on different events and attributes, as listed above. It performs the operation when you pick some object and then drop it at a specified location.

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