为什么gridpanel有的列值为undifined
jsonstore:{"totalCount":"3","JData":[{"UserID":"1","UserName":"12313"},{"UserID":"17","UserName":"123156456"},{"UserID":"18","UserName":"123123123"}]}
store fields: [ 'UserID', { name: 'UserName ', type: 'string'}]
grid cm:[ { header: "UserID", dataIndex: 'UserID', sortable: true },
{ header: "UserName", dataIndex: 'UserName', sortable: true}]