Issue
I am trying to move an element using drag and drop. I want to be able to drag and element to a different location, and when I drop it, the element moves to the dropped location. Super basic, and nothing fancy. This is what I have so far:
html:
<input type='button' id='drag' class='draggable' value='drag me' draggable='true'>
Dart code:
Element drag = querySelector('.draggable');
drag.onDragEnd.listen((MouseEvent e) {
drag.style.left = '${e.client.x}px';
drag.style.top = '${e.client.y}px';
});
This doesn’t quite do what I want it to do. The element is slightly off from where I drop it. I see examples in javascript with appendChild, clone(), parentNode, but none of the examples that I have seen can be reproduced in Dart. What is the best way to accomplish this? I don’t want to use the DND package, since I am really trying to personally understand the concepts better.
Solution
index.html
<!doctype html>
<html>
<head>
<style>
#dropzone {
position: absolute;
top: 50px;
left: 50px;
width: 300px;
height: 150px;
border: solid 1px lightgreen;
}
#dropzone.droptarget {
background-color: lime;
}
</style>
</head>
<body>
<input type='button' id='drag' class='draggable' value='drag me'
draggable='true'>
<div id="dropzone"></div>
<script type="application/dart" src="index.dart"></script>
<script src="packages/browser/dart.js"></script>
</body>
</html>
index.dart
library _template.web;
import 'dart:html' as dom;
import 'dart:convert' show JSON;
main() async {
dom.Element drag = dom.querySelector('.draggable');
drag.onDragStart.listen((event) {
final startPos = (event.target as dom.Element).getBoundingClientRect();
final data = JSON.encode({
'id': (event.target as dom.Element).id,
'x': event.client.x - startPos.left,
'y': event.client.y - startPos.top
});
event.dataTransfer.setData('text', data);
});
dom.Element dropTarget = dom.querySelector('#dropzone');
dropTarget.onDragOver.listen((event) {
event.preventDefault();
dropTarget.classes.add('droptarget');
});
dropTarget.onDragLeave.listen((event) {
event.preventDefault();
dropTarget.classes.remove('droptarget');
});
dropTarget.onDrop.listen((event) {
event.preventDefault();
final data = JSON.decode(event.dataTransfer.getData('text'));
final drag = dom.document.getElementById(data['id']);
event.target.append(drag);
drag.style
..position = 'absolute'
..left = '${event.offset.x - data['x']}px'
..top = '${event.offset.y - data['y']}px';
dropTarget.classes.remove('droptarget');
});
}
Answered By – Günter Zöchbauer
Answer Checked By – Cary Denson (FlutterFixes Admin)