YUI Library Examples: Drag & Drop: Reordering a List

Drag and Drop List Ordering

The YUI Drag & Drop Utility lets you make HTML elements draggable.

In this example, list reordering is implemented by extending YAHOO.util.DDProxy instead of YAHOO.util.DD so that we can use the source element as the "insertion point". When the drag starts, the proxy element style and content is adjusted to match the source element, and visibility:hidden is applied to the source element.

To facilitate dragging into an empty list, we make the two list elements DDTargets. When interacting with the list items, we will get two notifications (one for the list, one for the list item). We ignore all dragOver events that happen on the list and ignore all dragDrop events unless the drop was in the list's negative space (not over another list item).

Create the elements:

Now we create the instances of YAHOO.util.DDProxy, passing the element ids or references for our demo elements.

(function() {

var Dom = YAHOO.util.Dom;
var Event = YAHOO.util.Event;
var DDM = YAHOO.util.DragDropMgr;

//////////////////////////////////////////////////////////////////////////////
// example app
//////////////////////////////////////////////////////////////////////////////
YAHOO.example.DDApp = {
    init: function() {

var rows=3,cols=2,i,j;
        for (i=1;i<cols+1;i=i+1) {
            new YAHOO.util.DDTarget("ul"+i);
        }

for (i=1;i<cols+1;i=i+1) {
            for (j=1;j<rows+1;j=j+1) {
                new YAHOO.example.DDList("li" + i + "_" + j);
            }
        }

Event.on("showButton", "click", this.showOrder);
        Event.on("switchButton", "click", this.switchStyles);
    },

showOrder: function() {
        var parseList = function(ul, title) {
            var items = ul.getElementsByTagName("li");
            var out = title + ": ";
            for (i=0;i<items.length;i=i+1) {
                out += items[i].id + " ";
            }
            return out;
        };

var ul1=Dom.get("ul1"), ul2=Dom.get("ul2");
        alert(parseList(ul1, "List 1") + "\n" + parseList(ul2, "List 2"));

switchStyles: function() {
        Dom.get("ul1").className = "draglist_alt";
        Dom.get("ul2").className = "draglist_alt";
    }
};

//////////////////////////////////////////////////////////////////////////////
// custom drag and drop implementation
//////////////////////////////////////////////////////////////////////////////

YAHOO.example.DDList = function(id, sGroup, config) {

YAHOO.example.DDList.superclass.constructor.call(this, id, sGroup, config);

this.logger = this.logger || YAHOO;
    var el = this.getDragEl();
    Dom.setStyle(el, "opacity", 0.67); // The proxy is slightly transparent

this.goingUp = false;
    this.lastY = 0;
};

YAHOO.extend(YAHOO.example.DDList, YAHOO.util.DDProxy, {

startDrag: function(x, y) {
        this.logger.log(this.id + " startDrag");

// make the proxy look like the source element
        var dragEl = this.getDragEl();
        var clickEl = this.getEl();
        Dom.setStyle(clickEl, "visibility", "hidden");

dragEl.innerHTML = clickEl.innerHTML;

Dom.setStyle(dragEl, "color", Dom.getStyle(clickEl, "color"));
        Dom.setStyle(dragEl, "backgroundColor", Dom.getStyle(clickEl, "backgroundColor"));
        Dom.setStyle(dragEl, "border", "2px solid gray");
    },

endDrag: function(e) {

var srcEl = this.getEl();
        var proxy = this.getDragEl();

// Show the proxy element and animate it to the src element's location
        Dom.setStyle(proxy, "visibility", "");
        var a = new YAHOO.util.Motion( 
            proxy, { 
                points: { 
                    to: Dom.getXY(srcEl)
                }
            }, 
            0.2, 
            YAHOO.util.Easing.easeOut 
        );
        var proxyid = proxy.id;
        var thisid = this.id;

// Hide the proxy and show the source element when finished with the animation
        a.onComplete.subscribe(function() {
                Dom.setStyle(proxyid, "visibility", "hidden");
                Dom.setStyle(thisid, "visibility", "");
            });
        a.animate();
    },

onDragDrop: function(e, id) {

// If there is one drop interaction, the li was dropped either on the list,
        // or it was dropped on the current location of the source element.
        if (DDM.interactionInfo.drop.length === 1) {

// The position of the cursor at the time of the drop (YAHOO.util.Point)
            var pt = DDM.interactionInfo.point;

// The region occupied by the source element at the time of the drop
            var region = DDM.interactionInfo.sourceRegion;

// Check to see if we are over the source element's location.  We will
            // append to the bottom of the list once we are sure it was a drop in
            // the negative space (the area of the list without any list items)
            if (!region.intersect(pt)) {
                var destEl = Dom.get(id);
                var destDD = DDM.getDDById(id);
                destEl.appendChild(this.getEl());
                destDD.isEmpty = false;
                DDM.refreshCache();
            }

}
    },

onDrag: function(e) {

// Keep track of the direction of the drag for use during onDragOver
        var y = Event.getPageY(e);

if (y < this.lastY) {
            this.goingUp = true;
        } else if (y > this.lastY) {
            this.goingUp = false;
        }

this.lastY = y;
    },

onDragOver: function(e, id) {
    
        var srcEl = this.getEl();
        var destEl = Dom.get(id);

// We are only concerned with list items, we ignore the dragover
        // notifications for the list.
        if (destEl.nodeName.toLowerCase() == "li") {
            var orig_p = srcEl.parentNode;
            var p = destEl.parentNode;

if (this.goingUp) {
                p.insertBefore(srcEl, destEl); // insert above
            } else {
                p.insertBefore(srcEl, destEl.nextSibling); // insert below
            }

DDM.refreshCache();
        }
    }
});

Event.onDOMReady(YAHOO.example.DDApp.init, YAHOO.example.DDApp, true);

})();
</script>

YUI Logger Output:

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Drag & Drop Examples:

More Drag & Drop Resources:

All YUI 2.x users should review the YUI 2.8.2 security bulletin, which discusses a vulnerability present in YUI 2.4.0-2.8.1.