easyui 下拉宽出不来 不报错

        {field:'mem_Id',title:'会员等级',width:100,editor:{type:'text',options: {required: true}},sortable:true,formatter:function(value,index,row){
                      if(value==1){
                          return '普通会员';
                      }else if(value==2){
                          return '中等会员';
                      }else if(value==3){
                          return '高级会员';
                      }
                  },
                  editor:{
                        type:'combobox',
                        options:{    
                            valueField:'mem_grade',
                            textField:'mem_Id',
                            url:'member.action',
                            required:true,  

                        }}},

 返回的json数据{"total":3,"rows":[{"mem_Id":1,"mem_grade":"普通会员"},{"mem_Id":2,"mem_grade":"中等会员"},{"mem_Id":3,"mem_grade":"高级会员"}]}