dragdrop.js

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         * @type Object
         * @private
         */
        this.clickTimeout = null;

        /**
         * The X position of the mousedown event stored for later use when a
         * drag threshold is met.
         * @type int
         * @private
         */
        this.startX = 0;

        /**
         * The Y position of the mousedown event stored for later use when a
         * drag threshold is met.
         * @type int
         * @private
         */
        this.startY = 0;

        /**
         * Each DragDrop instance must be registered with the DragDropMgr.
         * This is executed in DragDrop.init()
         *
         * @param {DragDrop} oDD the DragDrop object to register
         * @param {String} sGroup the name of the group this element belongs to
         */
        this.regDragDrop = function(oDD, sGroup) {
            if (!this.initialized) { this.init(); }

            if (!this.ids[sGroup]) {
                this.ids[sGroup] = {};
            }
            this.ids[sGroup][oDD.id] = oDD;
        };

        /**
         * Removes the supplied dd instance from the supplied group. Executed
         * by DragDrop.removeFromGroup.
         * @private
         */
        this.removeDDFromGroup = function(oDD, sGroup) {
            if (!this.ids[sGroup]) {
                this.ids[sGroup] = {};
            }

            var obj = this.ids[sGroup];
            if (obj && obj[oDD.id]) {
                delete obj[oDD.id];
            }
        };

        /**
         * Unregisters a drag and drop item.  This is executed in
         * DragDrop.unreg, use that method instead of calling this directly.
         * @private
         */
        this._remove = function(oDD) {
            for (var g in oDD.groups) {
                if (g && this.ids[g][oDD.id]) {
                    delete this.ids[g][oDD.id];
                }
            }
            delete this.handleIds[oDD.id];
        };

        /**
         * Each DragDrop handle element must be registered.  This is done
         * automatically when executing DragDrop.setHandleElId()
         *
         * @param {String} sDDId the DragDrop id this element is a handle for
         * @param {String} sHandleId the id of the element that is the drag
         * handle
         */
        this.regHandle = function(sDDId, sHandleId) {
            if (!this.handleIds[sDDId]) {
                this.handleIds[sDDId] = {};
            }
            this.handleIds[sDDId][sHandleId] = sHandleId;
        };

        /**
         * Utility function to determine if a given element has been
         * registered as a drag drop item.
         *
         * @param {String} id the element id to check
         * @return {boolean} true if this element is a DragDrop item,
         * false otherwise
         */
        this.isDragDrop = function(id) {
            return ( this.getDDById(id) ) ? true : false;
        };

        /**
         * Returns the drag and drop instances that are in all groups the
         * passed in instance belongs to.
         *
         * @param {DragDrop} p_oDD the obj to get related data for
         * @param {boolean} bTargetsOnly if true, only return targetable objs
         * @return {DragDrop[]} the related instances
         */
        this.getRelated = function(p_oDD, bTargetsOnly) {
            var oDDs = [];
            for (var i in p_oDD.groups) {
                for (j in this.ids[i]) {
                    var dd = this.ids[i][j];
                    if (! this.isTypeOfDD(dd)) {
                        continue;
                    }
                    if (!bTargetsOnly || dd.isTarget) {
                        oDDs[oDDs.length] = dd;
                    }
                }
            }

            return oDDs;
        };

        /**
         * Returns true if the specified dd target is a legal target for
         * the specifice drag obj
         *
         * @param {DragDrop} the drag obj
         * @param {DragDrop) the target
         * @return {boolean} true if the target is a legal target for the
         * dd obj
         */
        this.isLegalTarget = function (oDD, oTargetDD) {
            var targets = this.getRelated(oDD, true);
            for (var i=0, len=targets.length;i<len;++i) {
                if (targets[i].id == oTargetDD.id) {
                    return true;
                }
            }

            return false;
        };

        /**
         * My goal is to be able to transparently determine if an object is
         * typeof DragDrop, and the exact subclass of DragDrop.  typeof
         * returns "object", oDD.constructor.toString() always returns
         * "DragDrop" and not the name of the subclass.  So for now it just
         * evaluates a well-known variable in DragDrop.
         *
         * @param {Object} the object to evaluate
         * @return {boolean} true if typeof oDD = DragDrop
         */
        this.isTypeOfDD = function (oDD) {
            return (oDD && oDD.__ygDragDrop);
        };

        /**
         * Utility function to determine if a given element has been
         * registered as a drag drop handle for the given Drag Drop object.
         *
         * @param {String} id the element id to check
         * @return {boolean} true if this element is a DragDrop handle, false
         * otherwise
         */
        this.isHandle = function(sDDId, sHandleId) {
            return ( this.handleIds[sDDId] &&
                            this.handleIds[sDDId][sHandleId] );
        };

        /**
         * Returns the DragDrop instance for a given id
         *
         * @param {String} id the id of the DragDrop object
         * @return {DragDrop} the drag drop object, null if it is not found
         */
        this.getDDById = function(id) {
            for (var i in this.ids) {
                if (this.ids[i][id]) {
                    return this.ids[i][id];
                }
            }
            return null;
        };

        /**
         * Fired after a registered DragDrop object gets the mousedown event.
         * Sets up the events required to track the object being dragged
         *
         * @param {Event} e the event
         * @param oDD the DragDrop object being dragged
         * @private
         */
        this.handleMouseDown = function(e, oDD) {

            this.currentTarget = YAHOO.util.Event.getTarget(e);

            this.dragCurrent = oDD;

            var el = oDD.getEl();

            // track start position
            this.startX = YAHOO.util.Event.getPageX(e);
            this.startY = YAHOO.util.Event.getPageY(e);

            this.deltaX = this.startX - el.offsetLeft;
            this.deltaY = this.startY - el.offsetTop;

            this.dragThreshMet = false;

            this.clickTimeout = setTimeout(
                    function() {
                        var DDM = YAHOO.util.DDM;
                        DDM.startDrag(DDM.startX, DDM.startY);
                    },
                    this.clickTimeThresh );
        };

        /**
         * Fired when either the drag pixel threshol or the mousedown hold
         * time threshold has been met.
         *
         * @param x {int} the X position of the original mousedown
         * @param y {int} the Y position of the original mousedown
         */
        this.startDrag = function(x, y) {
            clearTimeout(this.clickTimeout);
            if (this.dragCurrent) {
                this.dragCurrent.b4StartDrag(x, y);
                this.dragCurrent.startDrag(x, y);
            }
            this.dragThreshMet = true;
        };

        /**
         * Internal function to handle the mouseup event.  Will be invoked
         * from the context of the document.
         *
         * @param {Event} e the event
         * @private
         */
        this.handleMouseUp = function(e) {

            if (! this.dragCurrent) {
                return;
            }

            clearTimeout(this.clickTimeout);

            if (this.dragThreshMet) {
                this.fireEvents(e, true);
            } else {
            }

            this.stopDrag(e);

            this.stopEvent(e);
        };

        /**
         * Utility to stop event propagation and event default, if these
         * features are turned on.
         *
         * @param {Event} e the event as returned by this.getEvent()
         */
        this.stopEvent = function(e) {
            if (this.stopPropagation) {
                YAHOO.util.Event.stopPropagation(e);
            }

            if (this.preventDefault) {
                YAHOO.util.Event.preventDefault(e);
            }
        };

        /**
         * Internal function to clean up event handlers after the drag
         * operation is complete
         *
         * @param {Event} e the event
         * @private
         */
        this.stopDrag = function(e) {

            // Fire the drag end event for the item that was dragged
            if (this.dragCurrent) {
                if (this.dragThreshMet) {
                    this.dragCurrent.b4EndDrag(e);
                    this.dragCurrent.endDrag(e);
                }

                this.dragCurrent.onMouseUp(e);
            }

            this.dragCurrent = null;
            this.dragOvers = {};
        };

        /**
         * Internal function to handle the mousemove event.  Will be invoked
         * from the context of the html element.
         *
         * @TODO figure out what we can do about mouse events lost when the
         * user drags objects beyond the window boundary.  Currently we can
         * detect this in internet explorer by verifying that the mouse is
         * down during the mousemove event.  Firefox doesn't give us the
         * button state on the mousemove event.
         *
         * @param {Event} e the event
         * @private
         */
        this.handleMouseMove = function(e) {
            if (! this.dragCurrent) {
                return true;
            }

            // var button = e.which || e.button;

            // check for IE mouseup outside of page boundary
            if (YAHOO.util.Event.isIE && !e.button) {
                this.stopEvent(e);
                return this.handleMouseUp(e);
            }

            if (!this.dragThreshMet) {
                var diffX = Math.abs(this.startX - YAHOO.util.Event.getPageX(e));
                var diffY = Math.abs(this.startY - YAHOO.util.Event.getPageY(e));
                if (diffX > this.clickPixelThresh ||
                            diffY > this.clickPixelThresh) {
                    this.startDrag(this.startX, this.startY);
                }
            }

            if (this.dragThreshMet) {
                this.dragCurrent.b4Drag(e);
                this.dragCurrent.onDrag(e);
                this.fireEvents(e, false);
            }

            this.stopEvent(e);

            return true;
        };

        /**
         * Iterates over all of the DragDrop elements to find ones we are
         * hovering over or dropping on
         *
         * @param {Event} e the event
         * @param {boolean} isDrop is this a drop op or a mouseover op?
         * @private
         */
        this.fireEvents = function(e, isDrop) {
            var dc = this.dragCurrent;

            // If the user did the mouse up outside of the window, we could
            // get here even though we have ended the drag.
            if (!dc || dc.isLocked()) {
                return;
            }

            var x = YAHOO.util.Event.getPageX(e);
            var y = YAHOO.util.Event.getPageY(e);
            var pt = new YAHOO.util.Point(x,y);

            // cache the previous dragOver array
            var oldOvers = [];

            var outEvts   = [];
            var overEvts  = [];
            var dropEvts  = [];
            var enterEvts = [];

            // Check to see if the object(s) we were hovering over is no longer
            // being hovered over so we can fire the onDragOut event
            for (var i in this.dragOvers) {

                var ddo = this.dragOvers[i];

                if (! this.isTypeOfDD(ddo)) {
                    continue;
                }

                if (! this.isOverTarget(pt, ddo, this.mode)) {
                    outEvts.push( ddo );
                }

                oldOvers[i] = true;
                delete this.dragOvers[i];
            }

            for (var sGroup in dc.groups) {

                if ("string" != typeof sGroup) {
                    continue;
                }

                for (i in this.ids[sGroup]) {
                    var oDD = this.ids[sGroup][i];
                    if (! this.isTypeOfDD(oDD)) {
                        continue;
                    }

                    if (oDD.isTarget && !oDD.isLocked() && oDD != dc) {
                        if (this.isOverTarget(pt, oDD, this.mode)) {
                            // look for drop interactions
                            if (isDrop) {
                                dropEvts.push( oDD );
                            // look for drag enter and drag over interactions
                            } else {

                                // initial drag over: dragEnter fires
                                if (!oldOvers[oDD.id]) {
                                    enterEvts.push( oDD );
                                // subsequent drag overs: dragOver fires
                                } else {