react native AsyncStorage

componentDidMount() {
 let _that=this;
  AsyncStorage.getItem('userid',(err, result) => {
     console.log(result);
   var userid=result;
   var startday=this.state.startday;//set date
   var endday=this.state.endday;//set date
   console.log(userid);
   console.log(startday); //check date 
   console.log(endday);
   var url = 'http://47.90.60.206:8080/pt_server/sportchart.action'; // create url 
     // var url = 'http://192.168.20.12:8080/pt_server/traineelogin.action';
     url += '?userid='+userid+'&start='+startday+'&end='+endday;
     console.log(url); //check url 
     fetch(url).then(function(response) { 
           return response.json();
         }).then(function(res) {
         console.log(res);//check json,then render the view again 
           if (res["data"]!=null) {
             _that.setState(
             {

             }
           );

         }else{
           Alert.alert('error'); //alert warning and error 
         }
   });
 });
 }