mxGraph实现按住ctrl键盘拖动图形实现复制图形功能

实现这个功能很easy，仅仅须要重写moveCells方法就能够了。以下是源文件里的代码：

mxGraph.prototype.moveCells = function(cells, dx, dy, clone, target, evt) {
    if (cells != null && (dx != 0 || dy != 0 || clone || target != null)) {
        this.model.beginUpdate();
        try {
            if (clone) {
                cells = this.cloneCells(cells, this.isCloneInvalidEdges());
                if (target == null) {
                    target = this.getDefaultParent();
                }
            }
            this.cellsMoved(cells, dx, dy, !clone && this.isDisconnectOnMove() && this.isAllowDanglingEdges(), target == null);
            if (target != null) {
                var index = this.model.getChildCount(target);
                this.cellsAdded(cells, target, index, null, null, true);
            }
            this.fireEvent(new mxEventObject(mxEvent.MOVE_CELLS, 'cells', cells, 'dx', dx, 'dy', dy, 'clone', clone, 'target', target, 'event', evt));
        } finally {
            this.model.endUpdate();
        }
    }
    return cells;
};

mxGraph.prototype.moveCells = function(cells, dx, dy, clone, target, evt) {
     clone=evt.ctrlKey;//对。就是这啦！

     if (cells != null && (dx != 0 || dy != 0 || clone || target != null)) {
        this.model.beginUpdate();
        try {
            if (clone) {
                cells = this.cloneCells(cells, this.isCloneInvalidEdges());
                if (target == null) {
                    target = this.getDefaultParent();
                }
            }
            this.cellsMoved(cells, dx, dy, !clone && this.isDisconnectOnMove() && this.isAllowDanglingEdges(), target == null);
            if (target != null) {
                var index = this.model.getChildCount(target);
                this.cellsAdded(cells, target, index, null, null, true);
            }
            this.fireEvent(new mxEventObject(mxEvent.MOVE_CELLS, 'cells', cells, 'dx', dx, 'dy', dy, 'clone', clone, 'target', target, 'event', evt));
        } finally {
            this.model.endUpdate();
        }
    }
    return cells;
};