Limit Max Elements in Drag and Drop panel

I've got a sortable panel (jQuery UI) on my website, but need to limit the amount of elements in each column to a maximum of 12.

I've tried a few things, but can't seem to get it to work. I need to see if 'i' is 12 or greater, and if so, don't update but I can't seem to do it!

Anyone got any advice or can push me the right way?

The jQuery is below!

function updateWidgetData(){
    var items=[];
    $('.column').each(function(){
        var columnId=$(this).attr('id');
        $('.dragbox', this).each(function(i){
            var collapsed=0;
            if($(this).find(开发者_JS百科'.dragbox-content').css('display')=="none")
                collapsed=1;
            var item={
                id: $(this).attr('ID'),
                collapsed: collapsed,
                order : i,
                column: columnId
            };
            items.push(item);
        });
    });
    var sortorder={ items: items };

    //Pass sortorder variable to server using ajax to save state

    $.post('includes/updatePanels.php', 'data='+$.toJSON(sortorder), function(response){
        if(response=="success")
            $("#console").html('<div class="success">Your preferences have been saved</div>').hide().fadeIn(1000);
        setTimeout(function(){
            $('#console').fadeOut(1000);
        }, 2000);
    });
}

Sortables

For connected sortables, the solution is to count the elements in each sortable when dragging starts, and disable the ones which have the maximum number of allowed elements. We need to exclude the current sortable, so we can re-order the items within and allow the current element to be dragged.

The problem here is that if we do the above on any of the sortables' events, it's already too late and disabling them won't have any effect. The solution is to do the bind the check to the mousedown event of the items themselves, which will fire before the sortable would get any control. We also need to re-enable all sortables when dragging stops.

Have a look at this example, using <ul> sortables with <li> items, the maximum number of items in each sortable is 3: http://jsfiddle.net/qqqm6/10/

$('.sort').sortable({
    revert: 'invalid',
    connectWith: '.sort',
    stop: function(){
        // Enable all sortables
        $('.sort').each(function(){
            $(this).sortable('enable');
        });
    }
});

$('.sort li').mousedown(function(){
    // Check number of elements already in each sortable
    $('.sort').not($(this).parent()).each(function(){
        var $this = $(this);

        if($this.find('li').length >= 3){
            $this.sortable('disable');
        } else {
            $this.sortable('enable');
        }
    });
})

Draggables and droppables

The theory is simple, the solution is a bit tricky, there should really be a proper option in jQuery UI to cancel the operation on drop. If there is, but I missed something, please let me know.

Anyways, here's how you check for maximum count in the drop event (maximum of 4 in this example):

$('.drag').draggable({
    revert: 'invalid',
    stop: function(){
        // Make it properly draggable again in case it was cancelled
        $(this).draggable('option','revert','invalid');
    }
});

$('.drop').droppable({
    drop: function(event,ui){
        var $this = $(this);

        // Check number of elements already in
        if($this.find('.drag').length >= 4){
            // Cancel drag operation (make it always revert)
            ui.draggable.draggable('option','revert',true);
            return;
        }

        // Put dragged item into container
        ui.draggable.appendTo($this).css({
            top: '0px',
            left: '0px'
        });

        // Do whatever you want with ui.draggable, which is a valid dropped object
    }
});

See this fiddle in action: http://jsfiddle.net/qqqm6/