code: function(title,point,items){
      var _self = this,
        tooltip = _self.get('tipGroup'),
        prePoint = _self.get('prePoint');
      if(!prePoint || (prePoint.x != point.x || prePoint.y != point.y) || point.name != prePoint.name){
        tooltip.setPosition(point.x,point.y);
        _self.set('prePoint',point);
        if(!tooltip.get('visible')){
          tooltip.show();
        }
        tooltip.setTitle(title);
        tooltip.setItems(items); 
      }
    }
docs: 显示tooltip