jQuery draggable + droppable: how to snap dropped element to dropped-on element

Question

I have my screen divided into two DIVs. In the left DIV I have a few 50x50 pixel DIVs, in the right DIV I have an empty grid made of 80x80 LIs. The DIVs on the left are draggable, and once dropped on a LI, they should snap to center of that LI.

Sounds simple, right? I just don't know how to get this done. I tried by manipulating the dropped DIV's top and left CSS properties to match those of the LI they're dropped into, but the left and top properties are relative to the left DIV.

How can I best have the dropped element snap to the center of the element it's dropped into? That's gotta be simple, right?

Edit: I'm using jQuery UI 1.7.2 with jQuery 1.3.2.

Edit 2: For whoever else has this problem, this is how I fixed it:

I used Keith's solution of removing the dragged element and placing it inside the dropped-on element in the drop callback of the droppable plugin:

function gallerySnap(droppedOn, droppedElement)
{
    $(droppedOn).html('<div class="drop_styles">'+$(droppedElement).html()+'</div>' );
    $(droppedElement).remove();
}

I don't the dropped element to be draggable again, but if you do, just bind draggable to it again.

For me this method also solved the problem I had when positioning the dropped elements (which would be relative to the left DIV) and scrolling inside the second DIV. (Elements would remain fixed on page, now they scroll along).

I did play with the snap options to make it look good while dragging, so thanks to karim79 for that suggestion.

I probably won't win any Awesome Code prizes with this, so if you see room for improvement, please share!

Answer 1

Take a look at this demo, and view the source:

http://jquery-ui.googlecode.com/svn/trunk/demos/draggable/snap-to.html

Answer 2

If the DIVs on the left are actually IN the LIs on the right (which you can confirm with Firebug), and if the LIs are all in a UL (as they should be), try one or both of the following:

ul#right_div {
  text-align: center;
}

ul#right_div li {
  text-align: center;
}

Answer 3

I found that when you do the drag, jQuery UI adds an inline to tell you where you dropped it. Below is a sample of the code that I used to snap it into place

$('.droppable').droppable({
        drop: function(ev, ui) { 
         //Get Details of dragged and dropped
         var draggedclass = ui.draggable.attr('class');
         var droppedclass = 'class' + $(this).attr('name').toLowerCase();
         //update the classes so that it looks good.
         ui.draggable.removeClass(draggedclass).addClass(droppedclass); 
         ui.draggable.removeAttr('style');
        }
       });

Answer 4

I had a similar problem - I worked around it by manually removing the dragged element from its old parent and adding it to the dropped on element.

Answer 5

Thanks for your post - it helped me in the right direction. I find it a bit cleaner to set the position properties of the draggable object instead of messing with the html code. This sets the position to the top left corner of the droppable object, but you can modify to have it centered as well.

drop: function(event, ui) {
        $(ui.draggable).css('top',$(this).position().top);
        $(ui.draggable).css('left',$(this).position().left);
}

Answer 6

That function is nice but what is the droppedon value? What do you do to populated it?