在flutter应用程序中，我将JSON数据存储到两个字符串列表（化学名称和化学哈希）中。我使用这些字符串列表来检查在TextFormField中输入的文本是否与chemnames字符串列表中的字符串之一匹配。但是，当我调用.contains()方法时，我在控制台中收到一条错误消息：
The method 'contains' was called on null.
Receiver: null
Tried calling: contains("")
我需要添加什么来解决此错误？
这是我的代码：
import 'dart:ffi';
import 'dart:io';
import 'package:flutter/foundation.dart';
import 'dart:convert';
import 'dart:async';
import 'package:flutter/material.dart';
import 'package:http/http.dart' as http;
//import 'package:html/parser.dart'
class chemPage extends StatefulWidget{
@override
State<StatefulWidget> createState() {
return new chemicalResearchPage();
}
}
class chemicalResearchPage extends State<chemPage>{
final searchText = TextEditingController();
var crText = TextEditingController();
String chemText;
bool _value = false;
List<String> chemnames;
List<String> chemhashes;
List<String> chemnamesCleaned;
@override
void dispose() {
// Clean up the controller when the widget is disposed.
searchText.dispose();
super.dispose();
}
Future<String> getData(String hash) async{
var queryParameters = {
"chemID" : hash //just one of the hashes (example)
};
var uri =
Uri.https('www.myWebsite.com', '/api/getWebsite', queryParameters);
Icon searchIcon = Icon(Icons.search);
var objMapUrl = "https://MyWebsite.com/website";
Map data;
Map queryData;
http.Response response = await http.get(
Uri.encodeFull(objMapUrl),
headers: {
"key" : "fuiwefuiewfuqwf8uff"
}
);
var queryParams = await http.get(uri, headers: {
"key" : "fuiwefuiewfuqwf8uff"
});
data = json.decode(response.body);
//
// print(data["hashes"]);
// print( data["chem names"]);
// // print(data); //prints hashes
chemhashes = new List<String>.from(data["hashes"]);
chemnames = new List<String>.from(data["chem names"]);
// for(int i = 0; i < chemnames.length; i++){
// chemnamesCleaned[i] = chemnames[i].substring(chemnames.lastIndexOf("1"));
// }
print(chemhashes[10]);
print(chemnames);
//
//query parameters
queryData = json.decode(queryParams.body);
// print(queryData);
// print(chemnamesCleaned[5]);
chemText = queryData.toString();
//print(chemText);
setState(() {
crText.text = chemText;
});
return "Success";
}
@override
Widget build(BuildContext context) {
return Scaffold(
resizeToAvoidBottomPadding: false,
appBar: AppBar(
backgroundColor: Colors.white,
elevation: 0.0,
automaticallyImplyLeading: false,
title: Container(
margin: EdgeInsets.symmetric(horizontal: 1.0, vertical: 8.0),
decoration: BoxDecoration(
color: Colors.lightBlueAccent,
borderRadius: BorderRadius.all(Radius.circular(12.0)),
),
child: Row(
crossAxisAlignment: CrossAxisAlignment.start,
children: <Widget>[
Expanded(
flex: 1,
child: Container(
padding: EdgeInsets.symmetric(horizontal: 10.0),
child: TextFormField(
controller: searchText,
// textInputAction: TextInputAction.done,
onFieldSubmitted: (term){
if(chemnames.contains(searchText.text)){ //check if searchText is something
var index = chemnames.indexOf(searchText.text); //finds index of the c hemical name searched
getData(chemhashes[index]); //relates the index to find corresponding hash
}else{
AlertDialog dialog = new AlertDialog(
shape: RoundedRectangleBorder(
borderRadius: BorderRadius.all(Radius.circular(15.0))),
title: Text("Chemical not found", style: TextStyle(fontSize: 20.0),),
content: new Container(
width: 5.0,
height: 5.0,
),
actions: <Widget>[
new FlatButton(onPressed: (){
Navigator.pop(context);
}, child: new Text("Ok", style: TextStyle(fontSize: 20.0),))
],
);
showDialog(context: context, child: dialog);
}
},
cursorColor: Colors.white,
decoration: InputDecoration(
border: InputBorder.none,
hintText: "Enter Chemical Name",
hintStyle: TextStyle(color: Colors.white),
),
),
),
),
// Expanded(
// flex: 0,
// child: Container(
// padding: EdgeInsets.symmetric(horizontal: 0.0),
// child: Row(
// children: <Widget>[
// IconButton(
// onPressed: null,
// icon: Icon(Icons.search, color: Colors.white),
// ),
// ],
// ),
// ),
// ),
],
),
),
),
body: new Container(
child: SingleChildScrollView(
padding: new EdgeInsets.fromLTRB(25.0, 30.0, 25.0, 0.0),
child: Column(
crossAxisAlignment: CrossAxisAlignment.stretch,
mainAxisAlignment: MainAxisAlignment.center,
children: <Widget>[
new Text("Chemical Research", style: TextStyle(fontSize: 20, fontWeight: FontWeight.normal, color: Colors.lightBlue)),
new TextField(
decoration: new InputDecoration(
border: const OutlineInputBorder(
borderSide: const BorderSide(
color: Colors.blueGrey, width: 2.0
)
)
),
//textfield text needs to change to the text recieved from json.decode(queryParams.body) or chemText
controller: crText,
maxLines: 20,
),
Expanded(
flex: 0,
child: SingleChildScrollView(
padding: new EdgeInsets.fromLTRB(0.0, 45.0, 0.0, 0.0),
child: Align(
alignment: FractionalOffset.bottomCenter,
child: Container(
child: Column(
crossAxisAlignment: CrossAxisAlignment.stretch,
children: <Widget>[
new RaisedButton(onPressed: () {
if (chemnames.contains(searchText.text)){
var index = chemnames.indexOf(searchText.text); //finds index of the chemical name searched
getData(chemhashes[index]); //relates the index to find corresponding hash
// print(chemnamesCleaned[index]);
}else{
AlertDialog dialog = new AlertDialog(
shape: RoundedRectangleBorder(
borderRadius: BorderRadius.all(Radius.circular(15.0))),
title: Text("Chemical not found", style: TextStyle(fontSize: 20.0),),
content: new Container(
width: 5.0,
height: 5.0,
),
actions: <Widget>[
new FlatButton(onPressed: (){
Navigator.pop(context);
}, child: new Text("Ok", style: TextStyle(fontSize: 20.0),))
],
);
showDialog(context: context, child: dialog);
}
},
elevation: 2.0,
color: Colors.lightBlue,
child: Text("Search", style: TextStyle(color: Colors.white, fontSize: 20.0, fontWeight: FontWeight.bold)),
shape: RoundedRectangleBorder(
borderRadius: new BorderRadius.circular(15)
) ,
),
],
),
),
),
),)
],
),
),
),
);
}
}
.contains()方法的实现也在上述onSubmitted内部的代码段中。
if(chemnames.contains(searchText.text)){ //check if searchText is something
var index = chemnames.indexOf(searchText.text); //finds index of the c hemical name searched
getData(chemhashes[index]);