我有一个JSON应用程序调用用户,但我在处理null地图时遇到问题。
这是Json文件。
MemberInfo.json
{
"Dependents": [
{
"Name": "Kim",
"Relationship": "Parent",
"Entitlements": {
"GP": {
"Entitlement": "10000",
"Utilisation": "500",
"Balance": "9500"
},
"OPS": {
"Entitlement": "10000",
"Utilisation": "500",
"Balance": "9500"
},
"IP": {
"Entitlement": "50000",
"Utilisation": "17000",
"Balance": "33000"
}
}
},
{
"Name": "Tim",
"Relationship": "Spouse",
"Entitlements": {
"GP": {
"Entitlement": "10000",
"Utilisation": "500",
"Balance": "9500"
},
"OPS": {
"Entitlement": "10000",
"Utilisation": "500",
"Balance": "9500"
},
"IP": {
}
}
}
]
}
而dart文件如下:
import 'package:flutter/material.dart';
import 'dart:convert';
import 'dart:async';
import 'package:http/http.dart' as http;
final String url = "http://crm.emastpa.com.my/MemberInfo.json";
final String url2 = "http://crm.emastpa.com.my/MemberInfo2.json";
class Dependents extends StatelessWidget {
Dependents({Key key, this.index, this.name, this.page}) : super(key:key);
final int index;
final String name;
final int page;
Future<String> jsonContent() async {
var res = await http.get(
Uri.encodeFull(url2),
headers: {"Accept": "application/json"});
return res.body;
}
@override
Widget build(BuildContext context) {
Widget fifthBody = new Container(
child: new Center(
child: new FutureBuilder<String>(
future: jsonContent(),
builder: (context, snapshot){
if(snapshot.hasData){
List<Widget> widgets = [];
//get snapshot data from JSON tree
var jsondecode = json.decode(snapshot.data);
//[]->Entitlements
var jsonEntData = jsondecode["Dependents"][index]["Entitlements"];
//Everything under Entitlements
var jsonEntDataGP = jsonEntData["GP"];
var jsonEntDataOPS = jsonEntData["OPS"];
var jsonEntDataIP = jsonEntData["IP"];
//GP Branch
var gp_ent = jsonEntDataGP["Entitlement"];
var gp_util = jsonEntDataGP["Utilisation"];
var gp_bal = jsonEntDataGP["Balance"];
//OPS branch
var ops_ent = jsonEntDataOPS["Entitlement"];
var ops_util = jsonEntDataOPS["Utilisation"];
var ops_bal = jsonEntDataOPS["Balance"];
//IP branch
var ip_ent = jsonEntDataIP["Entitlement"];
var ip_util = jsonEntDataIP["Utilisation"];
var ip_bal = jsonEntDataIP["Balance"];
jsonEntDataGP != null?
widgets.add(new ExpansionTile(
title: new Text("GP"),
children: <Widget>[
new ListTile(
title: new Text("Entitlement"),
trailing: new Text(gp_ent),
)
],
))
: new Center();
jsonEntDataOPS != null?
widgets.add(new ExpansionTile(
title: new Text("OPS"),
children: <Widget>[
new ListTile(
title: new Text("Entitlement"),
trailing: new Text(ops_ent),
)
]))
: new Center();
jsonEntDataIP != null?
widgets.add(new ExpansionTile(
title: new Text("IP"),
children: <Widget>[
new ListTile(
title: new Text("Entitlement"),
trailing: new Text(ip_ent),
)
]))
: new Center();
return new Column(
children: widgets,
);
}else if(snapshot.hasError){
return new Text(snapshot.error);
}
//loading the page
return new Center(
child: new CircularProgressIndicator(),
);
}),
),
);
return MaterialApp(
home: Scaffold(
appBar: AppBar(
title: Text("$name + index: $index"),
),
body: fifthBody
),
);
}
}
这是我得到的错误:
I/flutter ( 8842): The following assertion was thrown building FutureBuilder<String>(dirty, state:
I/flutter ( 8842): _FutureBuilderState<String>#f9262):
I/flutter ( 8842): 'package:flutter/src/widgets/text.dart': Failed assertion: line 230 pos 15: 'data != null': is not
I/flutter ( 8842): true.
我正在尝试构建用户权利列表,但我不确定如何处理诸如“IP”之类的空键。只要键具有值内部,该应用程序就可以工作,但如果键为空,则会返回异常。
我该如何处理这个问题?
IP是空的JsonObject
"IP": {},
因此,当您尝试访问IP对象的数据时,它将返回null并将其传递给textview,以后数据为null错误。
你试图从没有键的json对象获取数据
var ip_ent = jsonEntDataIP["Entitlement"];
以后用作
new Text(ip_ent)
要解决此问题,您需要在变量为null的情况下指定默认值,或者可以将该视图隐藏为您的要求。
要在null的情况下指定默认值,请执行此操作。
var ip_ent = jsonEntDataIP["Entitlement"] ?? '';
var jsonEntDataIP = jsonEntData["IP"] ?? '';