这是一个简单的联系人应用程序，可以添加查看和编辑个人的联系人详细信息。我无法完全理解这里的错误。
class ViewContact extends StatefulWidget {
final String id;
ViewContact(this.id);
@override
_ViewContactState createState() => _ViewContactState(this.id);
}
class _ViewContactState extends State<ViewContact> {
DatabaseReference _databaseReference = FirebaseDatabase.instance.reference();
String mascot = "https://learncodeonline.in/mascot.png";
String id;
_ViewContactState(id);
Contact _contact;
bool isLoading = true;
getContact(id) async {
_databaseReference.child(id).onValue.listen ((event){
setState(() {
print(event.snapshot);
_contact = Contact.fromSnapshot(event.snapshot);
isLoading = false;
print(_contact.lastName);
});
});
}
@override
void initState(){
super.initState();
this.getContact(id);
}
callAction(String number) async{
String url = 'tel: $number';
if (await canLaunch(url)){
await launch(url);
}
else {
throw 'Could call $number';
}
}
smsAction(String number) async{
String url ='sms: $number';
if (await canLaunch(url)){
await launch(url);
}
else {
throw 'lol';
}
}
navigateToLastScreen(){
Navigator.pop(context);
}
navigateToEditScreen(id){
Navigator.push(context, MaterialPageRoute(builder: (context){
return EditContact();
}));
}
下面显示的错误。错误可能是由于id变量引起的吗？ （对Flutter来说是个新手）。
[ERROR:flutter/lib/ui/ui_dart_state.cc(148)] Unhandled Exception: NoSuchMethodError: The method 'split' was called on null.
E/flutter (12369): Receiver: null
E/flutter (12369): Tried calling: split("/")
E/flutter (12369): #0 Object.noSuchMethod (dart:core-patch/object_patch.dart:50:5)
E/flutter (12369): #1 DatabaseReference.child (package:firebase_database/src/database_reference.dart:24:58)
E/flutter (12369): #2 _ViewContactState.getContact (package:firebase_authentication/screens/view_contact.dart:24:25)
E/flutter (12369): <asynchronous suspension>
E/flutter (12369): #3 _ViewContactState.initState (package:firebase_authentication/screens/view_contact.dart:36:10)
E/flutter (12369): #4 StatefulElement._firstBuild (package:flutter/src/widgets/framework.dart:4033:58)
E/flutter (12369): #5 ComponentElement.mount (package:flutter/src/widgets/framework.dart:3902:5)
E/flutter (12369): #6 Element.inflateWidget (package:flutter/src/widgets/framework.dart:3084:14)
E/flutter (12369): #7 Element.updateChild (package:flutter/src/widgets/framework.dart:2887:12)
E/flutter (12369): #8 SingleChildRenderObjectElement.mount (package:flutter/src/widgets/framework.dart:5092:14)
E/flutter (12369): #9 Element.inflateWidget (package:flutter/src/widgets/framework.dart:3084:14)
E/flutter (12369): #10 Element.updateChild (package:flutter/src/widgets/framework.dart:2887:12)
E/flutter (12369): #11 ComponentElement.performRebuild (package:flutter/src/widgets/framework.dart:3935:16)
E/flutter (12369): #12 Element.rebuild (package:flutter/src/widgets/framework.dart:3721:5)
E/flutter (12369): #13 ComponentElement._firstBuild (package:flutter/src/widgets/framework.dart:3907:5)
E/flutter (12369): #14 ComponentElement.mount (package:flutter/src/widgets/framework.dart:3902:5)
E/flutter (12369): #15 Element.inflateWidget (package:flutter/src/widgets/framework.dart:3084:14)
E/flutter (12369): #16 Element.updateChild (package:flutter/src/widgets/framework.dart:2887:12)
E/flutter (12369): #17 SingleChildRenderObjectElement.mount (package:flutter/src/widgets/framework.dart:5092:14)
E/flutter (12369): #18 Element.inflateWidget (package:flutter/src/widgets/framework.dart:3084:14)
E/flutter (12369): #19 Element.updateChild (package:flutter/src/widgets/framework.dart:2887:12)
E/flutter (12369): #20 SingleChildRenderObjectElement.mount (package:flutter/src/widgets/framework.dart:5092:14)
E/flutter (12369): #21 Element.inflateWidget (package:flutter/src/widgets/framework.dart:3084:14)
E/flutter (12369): #22 Element.updateChild (package:flutter/src/widgets/framework.dart:2887:12)
E/flutter (12369): #23 SingleChildRenderObjectElement.mount (package:flutter/src/widgets/framework.dart:5092:14)
E/flutter (12369): #24 Element.inflateWidget (package:flutter/src/widgets/framework.dart:3084:14)
E/flutter (12369): #25 Element.updateChild (package:flutter/src/widgets/framework.dart:2887:12)
E/flutter (12369): #26 SingleChildRenderObjectElement.mount (package:flutter/src/widgets/framework.dart:5092:14)
E/flutter (12369): #27 Element.inflateWidget (package:flutter/src/widgets/framework.dart:3084:14)
E/flutter (12369): #28 Element.updateChild (package:flutter/src/widgets/framework.dart:2887:12)
E/flutter (12369): #29 ComponentElement.performRebuild (package:flutter/src/widgets/framework.dart:3935:16)
E/flutter (12369): #30 Element.rebuild (package:flutter/src/widgets/framework.dart:3721:5)
E/flutter (12369): #31 ComponentElement._firstBuild (package:flutter/src/widgets/framework.dart:3907:5)
E/flutter (12369): #32 StatefulElement._firstBuild (package:flutter/src/widgets/framework.dart:4053:11)
E/flutter (12369): #33 ComponentElement.mount (package:flutter/src/widgets/framework.dart:3902:5)
E/flutter (12369): #34 Element.inflateWidget (package:flutter/src/widgets/framework.dart:3084:14)
E/flutter (12369): #35 Element.updateChild (package:flutter/src/widgets/framework.dart:2887:12)
E/flutter (12369): #36 ComponentElement.performRebuild (package:flutter/src/widgets/framework.dart:3935:16)
E/flutter (12369): #37 Element.rebuild (package:flutter/src/widgets/framework.dart:3721:5)
E/flutter (12369): #38 ComponentElement._firstBuild (package:flutter/src/widgets/framework.dart:3907:5)
E/flutter (12369): #39 ComponentElement.mount (package:flutter/src/widgets/framework.dart:3902:5)
E/flutter (12369): #40 Element.inflateWidget (package:flutter/src/widgets/framework.dart:3084:14)
E/flutter (12369): #41 Element.updateChild (package:flutter/src/widgets/framework.dart:2887:12)
E/flutter (12369): #42 ComponentElement.performRebuild (package:flutter/src/widgets/framework.dart:3935:16)
E/flutter (12369): #43 Element.rebuild (package:flutter/src/widgets/framework.dart:3721:5)
E/flutter (12369): #44 ComponentElement._firstBuild (package:flutter/src/widgets/framework.dart
这是我面临的堆栈溢出错误。与上一个错误一样，我也无法弄清楚这个错误：（
I/flutter ( 4594): The following StackOverflowError was thrown building ViewContact(dirty, state:
I/flutter ( 4594): _ViewContactState#4e21c):
I/flutter ( 4594): Stack Overflow
I/flutter ( 4594):
I/flutter ( 4594): When the exception was thrown, this was the stack:
I/flutter ( 4594): #0 Contact.email (package:firebase_authentication/model/contact.dart:25:4)
I/flutter ( 4594): #1 Contact.email (package:firebase_authentication/model/contact.dart:25:29)
I/flutter ( 4594): #2 Contact.email (package:firebase_authentication/model/contact.dart:25:29)
I/flutter ( 4594): #3 Contact.email (package:firebase_authentication/model/contact.dart:25:29)
I/flutter ( 4594): #4 Contact.email (package:firebase_authentication/model/contact.dart:25:29)
I/flutter ( 4594): #5 Contact.email (package:firebase_authentication/model/contact.dart:25:29)
I/flutter ( 4594): #6 Contact.email (package:firebase_authentication/model/contact.dart:25:29)
I/flutter ( 4594): #7 Contact.email (package:firebase_authentication/model/contact.dart:25:29)
I/flutter ( 4594): #8 Contact.email (package:firebase_authentication/model/contact.dart:25:29)
I/flutter ( 4594): #9 Contact.email (package:firebase_authentication/model/contact.dart:25:29)
I/flutter ( 4594): #10 Contact.email (package:firebase_authentication/model/contact.dart:25:29)
I/flutter ( 4594): #11 Contact.email (package:firebase_authentication/model/contact.dart:25:29)
I/flutter ( 4594): #12 Contact.email (package:firebase_authentication/model/contact.dart:25:29)
I/flutter ( 4594): #13 Contact.email (package:firebase_authentication/model/contact.dart:25:29)
I/flutter ( 4594): #14 Contact.email (package:firebase_authentication/model/contact.dart:25:29)
I/flutter ( 4594): #15 Contact.email (package:firebase_authentication/model/contact.dart:25:29)
I/flutter ( 4594): #16 Contact.email (package:firebase_authentication/model/contact.dart:25:29)
I/flutter ( 4594): #17 Contact.email (package:firebase_authentication/model/contact.dart:25:29)
I/flutter ( 4594): #18 Contact.email (package:firebase_authentication/model/contact.dart:25:29)
I/flutter ( 4594): #19 Contact.email (package:firebase_authentication/model/contact.dart:25:29)
I/flutter ( 4594): #20 Contact.email (package:firebase_authentication/model/contact.dart:25:29)
I/flutter ( 4594): #21 Contact.email (package:firebase_authentication/model/contact.dart:25:29)
I/flutter ( 4594): #22 Contact.email (package:firebase_authentication/model/contact.dart:25:29)
I/flutter ( 4594): #23 Contact.email (package:firebase_authentication/model/contact.dart:25:29)
I/flutter ( 4594): #24 Contact.email (package:firebase_authentication/model/contact.dart:25:29)
I/flutter ( 4594): #25 Contact.email (package:firebase_authentication/model/contact.dart:25:29)
I/flutter ( 4594): #26 Contact.email (package:firebase_authentication/model/contact.dart:25:29)
I/flutter ( 4594): #27 Contact.email (package:firebase_authentication/model/contact.dart:25:29)
I/flutter ( 4594): #28 Contact.email (package:firebase_authentication/model/contact.dart:25:29)
I/flutter ( 4594): #29 Contact.email (package:firebase_authentication/model/contact.dart:25:29)
I/flutter ( 4594): #30 Contact.email (package:firebase_authentication/model/contact.dart:25:29)
I/flutter ( 4594): #31 Contact.email (package:firebase_authentication/model/contact.dart:25:29)
I/flutter ( 4594): #32 Contact.email (package:firebase_authentication/model/contact.dart:25:29)
I/flutter ( 4594): #33 Contact.email (package:firebase_authentication/model/contact.dart:25:29)
I/flutter ( 4594): #34 Contact.email (package:firebase_authentication/model/contact.dart:25:29)
I/flutter ( 4594): #35 Contact.email (package:firebase_authentication/model/contact.dart:25:29)
I/flutter ( 4594): #36 Contact.email (package:firebase_authentication/model/contact.dart:25:29)
I/flutter ( 4594): #37 Contact.email (package:firebase_authentication/model/contact.dart:25:29)
I/flutter ( 4594): #38 Contact.email (package:firebase_authentication/model/contact.dart:25:29)
I/flutter ( 4594): #39 Contact.email (package:firebase_authentication/model/contact.dart:25:29)
I/flutter ( 4594): #40 Contact.email (package:firebase_authentication/model/contact.dart:25:29)
I/flutter ( 4594): #41 Contact.email (package:firebase_authentication/model/contact.dart:25:29)
I/flutter ( 4594): #42 Contact.email (package:firebase_authentication/model/contact.dart:25:29)
I/flutter ( 4594): #43 Contact.email (package:firebase_authentication/model/contact.dart:25:29)
I/flutter ( 4594): ...
I/flutter ( 4594): ...
I/flutter ( 4594): #59478 Contact.email (package:firebase_authentication/model/contact.dart:25:29)
I/flutter ( 4594): #59479 Contact.email (package:firebase_authentication/model/contact.dart:25:29)
I/flutter ( 4594): #59480 Contact.email (package:firebase_authentication/model/contact.dart:25:29)
I/flutter ( 4594): #59481 Contact.email (package:firebase_authentication/model/contact.dart:25:29)
I/flutter ( 4594): #59482 Contact.email (package:firebase_authentication/model/contact.dart:25:29)
I/flutter ( 4594): #59483 Contact.email (package:firebase_authentication/model/contact.dart:25:29)
I/flutter ( 4594): #59484 Contact.email (package:firebase_authentication/model/contact.dart:25:29)
I/flutter ( 4594): #59485 Contact.email (package:firebase_authentication/model/contact.dart:25:29)
I/flutter ( 4594): #59486 Contact.email (package:firebase_authentication/model/contact.dart:25:29)
I/flutter ( 4594): #59487 Contact.email (package:firebase_authentication/model/contact.dart:25:29)
I/flutter ( 4594): #59488 Contact.email (package:firebase_authentication/model/contact.dart:25:29)
I/flutter ( 4594): #59489 Contact.email (package:firebase_authentication/model/contact.dart:25:29)
I/flutter ( 4594): #59490 Contact.email (package:firebase_authentication/model/contact.dart:25:29)
I/flutter ( 4594): #59491 Contact.email (package:firebase_authentication/model/contact.dart:25:29)
I/flutter ( 4594): #59492 Contact.email (package:firebase_authentication/model/contact.dart:25:29)
I/flutter ( 4594): #59493 Contact.email (package:firebase_authentication/model/contact.dart:25:29)
I/flutter ( 4594): #59494 Contact.email (package:firebase_authentication/model/contact.dart:25:29)
I/flutter ( 4594): #59495 Contact.email (package:firebase_authentication/model/contact.dart:25:29)
I/flutter ( 4594): #59496 Contact.email (package:firebase_authentication/model/contact.dart:25:29)
I/flutter ( 4594): #59497 Contact.email (package:firebase_authentication/model/contact.dart:25:29)
I/flutter ( 4594): #59498 Contact.email (package:firebase_authentication/model/contact.dart:25:29)
I/flutter ( 4594): #59499 Contact.email (package:firebase_authentication/model/contact.dart:25:29)
I/flutter ( 4594): #59500 Contact.email (package:firebase_authentication/model/contact.dart:25:29)
I/flutter ( 4594): #59501 Contact.email (package:firebase_authentication/model/contact.dart:25:29)
I/flutter ( 4594): #59502 Contact.email (package:firebase_authentication/model/contact.dart:25:29)
I/flutter ( 4594): #59503 Contact.email (package:firebase_authentication/model/contact.dart:25:29)
I/flutter ( 4594): #59504 _ViewContactState.build (package:firebase_authentication/screens/view_contact.dart:179:40)
I/flutter ( 4594): #59505 StatefulElement.build (package:flutter/src/widgets/framework.dart:4012:27)
I/flutter ( 4594): #59506 ComponentElement.performRebuild (package:flutter/src/widgets/framework.dart:3924:15)
I/flutter ( 4594): #59507 Element.rebuild (package:flutter/src/widgets/framework.dart:3721:5)
I/flutter ( 4594): #59508 BuildOwner.buildScope (package:flutter/src/widgets/framework.dart:2340:33)
I/flutter ( 4594): #59509 _WidgetsFlutterBinding&BindingBase&GestureBinding&ServicesBinding&SchedulerBinding&PaintingBinding&SemanticsBinding&RendererBinding&WidgetsBinding.drawFrame (package:flutter/src/widgets/binding.dart:700:20)
I/flutter ( 4594): #59510 _WidgetsFlutterBinding&BindingBase&GestureBinding&ServicesBinding&SchedulerBinding&PaintingBinding&SemanticsBinding&RendererBinding._handlePersistentFrameCallback (package:flutter/src/rendering/binding.dart:285:5)
I/flutter ( 4594): #59511 _WidgetsFlutterBinding&BindingBase&GestureBinding&ServicesBinding&SchedulerBinding._invokeFrameCallback (package:flutter/src/scheduler/binding.dart:1016:15)
I/flutter ( 4594): #59512 _WidgetsFlutterBinding&BindingBase&GestureBinding&ServicesBinding&SchedulerBinding.handleDrawFrame (package:flutter/src/scheduler/binding.dart:958:9)
I/flutter ( 4594): #59513 _WidgetsFlutterBinding&BindingBase&GestureBinding&ServicesBinding&SchedulerBinding._handleDrawFrame (package:flutter/src/scheduler/binding.dart:874:5)
I/flutter ( 4594): #59517 _invoke (dart:ui/hooks.dart:236:10)
I/flutter ( 4594): #59518 _drawFrame (dart:ui/hooks.dart:194:3)
I/flutter ( 4594): (elided 3 frames from package dart:async)
================================================ ================================ 这是与“查看联系人”状态关联的窗口小部件。
@override
Widget build(BuildContext context) {
return Scaffold(
appBar: AppBar(
title: Text("Add Contact"),
centerTitle: true,
leading: IconButton(
icon: Icon(Icons.arrow_back_ios),
onPressed: (){navigateToLastScreen(context);},
),
),
body: Container(
padding: EdgeInsets.all(20.0),
child: ListView(
children: <Widget>[
Container(
margin: EdgeInsets.only(top: 20.0),
child: GestureDetector(
onTap: (){
this.pickImage();
},
child: Center(
child: Container(
width: 130.0,
height: 130.0,
decoration: BoxDecoration(
border: Border.all(color: Colors.white, width: 4.0),
shape: BoxShape.circle,
image: DecorationImage(
fit: BoxFit.fill,
image: _photoUrl=="empty"? NetworkImage("https://i.imgur.com/BoN9kdC.png"): NetworkImage(_photoUrl),
),
),
),
),
),
),
Container(
margin: EdgeInsets.only(top: 40.0),
child: TextField(
onChanged: (value){
setState(() {
_firstName = value;
});
},
decoration: InputDecoration(
labelText: 'First Name',
border: OutlineInputBorder(
borderRadius: BorderRadius.circular(10.0),
),
),
),
),
Container(
margin: EdgeInsets.only(top: 20.0),
child: TextField(
onChanged: (value){
setState(() {
_lastName = value;
});
},
decoration: InputDecoration(
labelText: 'Last Name',
border: OutlineInputBorder(
borderRadius: BorderRadius.circular(10.0),
),
),
),
),
Container(
margin: EdgeInsets.only(top: 20.0),
child: TextField(
onChanged: (value){
setState(() {
_email = value;
});
},
decoration: InputDecoration(
labelText: 'E-mail',
border: OutlineInputBorder(
borderRadius: BorderRadius.circular(10.0),
),
),
),
),
Container(
margin: EdgeInsets.only(top: 20.0),
child: TextField(
onChanged: (value){
setState(() {
_phone = value;
});
},
decoration: InputDecoration(
labelText: 'Phone',
border: OutlineInputBorder(
borderRadius: BorderRadius.circular(10.0),
),
),
),
),
Container(
margin: EdgeInsets.only(top: 20.0),
child: TextField(
onChanged: (value){
setState(() {
_address = value;
});
},
decoration: InputDecoration(
labelText: 'Address',
border: OutlineInputBorder(
borderRadius: BorderRadius.circular(10.0),
),
),
),
),
//save the shit
Container(
padding: EdgeInsets.only(top: 20.0),
child: RaisedButton(
color: Colors.teal,
shape: RoundedRectangleBorder(borderRadius: BorderRadius.circular(20.0)),
padding: EdgeInsets.fromLTRB(50, 10, 50, 10),
onPressed: (){
saveContact(context);
},
child: Text("ADD CONTACT", style: TextStyle(color: Colors.white, fontSize: 20.0, fontWeight: FontWeight.bold),),
),
),
],
),
),
);
}
}
答案 0 :(得分：1)
我相信 id为空。
pip install filename.whl在堆栈跟踪之后，此行引发异常：
E/flutter (12369): #2 _ViewContactState.getContact (package:firebase_authentication/screens/view_contact.dart:24:25)
_databaseReference.child(id).onValue.listen((event)
从database_reference.dart第19-25行开始：
E/flutter (12369): #1 DatabaseReference.child (package:firebase_database/src/database_reference.dart:24:58)
路径是您的ID，所以我会说ID为空。
/// Gets a DatabaseReference for the location at the specified relative
/// path. The relative path can either be a simple child key (e.g. ‘fred’) or
/// a deeper slash-separated path (e.g. ‘fred/name/first’).
DatabaseReference child(String path) {
return DatabaseReference._(_database,
(List<String>.from(_pathComponents)..addAll(path.split('/'))));
}
您可以将断言添加到构造函数中，如果id为null，则将引发错误，然后您可以按照stacktrace查找损坏的代码。
E/flutter (12369): Receiver: null
E/flutter (12369): Tried calling: split("/")
编辑：
＃1
更改此行：
class ViewContact extends StatefulWidget {
final String id;
const ViewContact({Key key, @required this.id})
: assert(id != null),
super(key: key);
@override
_ViewContactState createState() => _ViewContactState(this.id);
}
到
_ViewContactState(id);
状态中的字段ID永远不会更新！
＃2
您可以通过调用 widget.id
访问Widget类中归档的ID。
id永远不会更改，不要将其放入State构造函数。
这应该有效
_ViewContactState(this.id);
答案 1 :(得分：1)
您应该使用
_ViewContactState(this.id);
初始化ID。否则它将为null，从而导致错误。
但是您实际上并不需要传递它，因为StatefulWidget可以通过 widget 调用
来访问它。class ViewContact extends StatefulWidget {
final String id;
ViewContact(this.id);
@override
_ViewContactState createState() => _ViewContactState();
}
class _ViewContactState extends State<ViewContact> {
DatabaseReference _databaseReference = FirebaseDatabase.instance.reference();
String mascot = "https://learncodeonline.in/mascot.png";
_ViewContactState();
Contact _contact;
bool isLoading = true;
getContact(id) async {
_databaseReference.child(id).onValue.listen ((event){
setState(() {
print(event.snapshot);
_contact = Contact.fromSnapshot(event.snapshot);
isLoading = false;
print(_contact.lastName);
});
});
}
@override
void initState(){
super.initState();
this.getContact(widget.id);
}