Event propagation, overlay and drag-and-drop events

12
votes

I want to overlay a div over the viewport when the user drags a file onto the window.

However, I'm having trouble with the event propagation. When I set the overlay to display: block it appears to fire off a dragleave event and then another dragenter and then another dragleave again, so it's always in a post-dragleave state. Of course I call e.stopPropagation() and e.preventDefault() on the event object, but it doesn't seem to make a difference.

The console.log() output when you drag something over the window:

dragenter
dragenter
dragleave
dragenter
dragleave

The css. #overlay is set to display: none by default, but will show if body has the dragenter class:

    body {
        position: absolute;
        height: auto;
        top: 0;
        left: 0;
        right: 0;
        bottom: 0;
        margin: 0;
        padding: 0;
    }

    #overlay {
        position: absolute;        
        height: auto;
        width: auto;
        top: 0;
        left: 0;
        right: 0;
        bottom: 0;
        background: url(bg.png) repeat-x top right, url(bg.png) repeat-x bottom left, url(bg.png) repeat-y top right, url(bg.p
ng) repeat-y bottom left;
        display: none;
    }

    body.dragenter #overlay {
        display: block;
    }

The javascript. Add the 'dragenter' class on dragenter and removes it on dragleave:

$(document).on('dragenter', function (e) {
    e.stopPropagation();
    e.preventDefault();
    console.log('dragenter');
    $(document.body).addClass('dragenter');
});

$(document).on('dragleave', function (e) {
    e.stopPropagation();
    e.preventDefault();
    console.log('dragleave';
    $(document.body).removeClass('dragenter');
});

The html:

<body>
<div id="overlay">...</div>
...    
</body>
4
javascriptjquerycsshtmljavascript-events

4 Answers

1
votes

Thanks to Scottux, that led me onto the right track.

Only problem was it also covered up the rest of the page, so none of the elements or inputs were clickable. I had to hide #dragOverlay by default with "display: none" and display it on this event

// Display an overlay when dragging a file over
$('*:visible').live('dragenter', function(e) {
    e.stopPropagation();
    $('body').addClass('drag-enter');
});
6
votes

Your overlay takes up the whole document size, when you drag in, it fills up its space and your mouse is effectively taken out of the body and is now over the overlay. This triggers a mouseleave/mouseenter loop. To achieve what you are after, you may want to bind the event to a transparent overlay with a high z-index over the visible overlay which has a lower z-index. This would keep the event in the highest element.

Example:

http://jsfiddle.net/scottux/z7yaB/

0
votes
    var dropZone = function() {
        var self = this;
        this.eTimestamp = 0;
        this.showDropZone = function(e) {
            e.stopPropagation();
            e.preventDefault();
            if (self.eTimestamp + 300 < e.timeStamp) {
                $("#coverDropZone").show();
                self.eTimestamp = e.timeStamp;
            }
            return false;
        }
        this.hideDropZone = function(e) {
            e.stopPropagation();
            e.preventDefault();
            if (self.eTimestamp + 300 < e.timeStamp) {
                $("#coverDropZone").hide();
                self.eTimestamp = e.timeStamp;
            }
            return false;
        }
        this.showImage = function(e) {
            e.stopPropagation();
            e.preventDefault();
            console.log(e);
            return false;
        }
        document.addEventListener('dragenter', self.showDropZone, false);
        document.addEventListener('dragleave', self.hideDropZone, false);
        document.addEventListener('drop', self.showImage, false);
    }
-1
votes

The simple solution is instead of using dragenter use dragover

dragover This event is fired as the mouse is moved over an element when a drag is occurring. Much of the time, the operation that occurs during a listener will be the same as the dragenter event.