var Dragging=function(validateHandler){ //参数为验证点击区域是否为可移动区域，如果是返回欲移动元素，负责返回null
                var draggingObj=null; //dragging Dialog
                var diffX=0;
                var diffY=0;
                
                function mouseHandler(e){
                    switch(e.type){
                        case 'mousedown':
                            draggingObj=validateHandler(e);//验证是否为可点击移动区域
                            if(draggingObj!=null){
                                diffX=e.clientX-draggingObj.offsetLeft;
                                diffY=e.clientY-draggingObj.offsetTop;
                            }
                            break;
                        
                        case 'mousemove':
                            if(draggingObj){
                                draggingObj.style.left=(e.clientX-diffX)+'px';
                                draggingObj.style.top=(e.clientY-diffY)+'px';
                            }
                            break;
                        
                        case 'mouseup':
                            draggingObj =null;
                            diffX=0;
                            diffY=0;
                            break;
                    }
                };
                
                return {
                    enable:function(){
                        document.addEventListener('mousedown',mouseHandler);
                        document.addEventListener('mousemove',mouseHandler);
                        document.addEventListener('mouseup',mouseHandler);
                    },
                    disable:function(){
                        document.removeEventListener('mousedown',mouseHandler);
                        document.removeEventListener('mousemove',mouseHandler);
                        document.removeEventListener('mouseup',mouseHandler);
                    }
                }
            }

            function getDraggingDialog(e){
                var target=e.target;
                while(target && target.className.indexOf('dialog-chat')==-1){
                    target=target.offsetParent;
                }
                if(target!=null){
                    return target.offsetParent;
                }else{
                    return null;
                }
            }
            
            Dragging(getDraggingDialog).enable();