我正在使用 Flutter 构建一个应用程序。将用户注册数据发布到数据库中，并且登录后进展顺利。但是在仪表板上我根本无法发布数据。
我的页面表单：
final GlobalKey<FormState> _formKey = GlobalKey<FormState>();
class MainScreen4 extends StatelessWidget {
final BuildContext menuScreenContext;
final Function onScreenHideButtonPressed;
final bool hideStatus;
String message;
BuildContext context;
Future<void> send() async {
_formKey.currentState.save();
print("field: $message");
Provider.of<SavingProvider>(context, listen: false)
.storeMessage(message)
.then((res) {
if (res != null) {
print('Success');
} else {
print('Failed');
}
});
}
MainScreen4(
{Key key,
this.menuScreenContext,
this.onScreenHideButtonPressed,
this.hideStatus = false})
: super(key: key);
@override
Widget build(BuildContext context) {
return Scaffold(
backgroundColor: Colors.grey.shade300,
appBar: AppBar(
centerTitle: true,
title: const Text('Pesan'),
),
body: Stack(
children: <Widget>[
Container(
padding: EdgeInsets.only(bottom: 50),
margin: EdgeInsets.all(10),
child: FutureBuilder(
future: Provider.of<SavingProvider>(context, listen: false)
.customerMessage(),
builder: (context, snapshot) {
return Consumer<SavingProvider>(
builder: (context, data, _) {
return ListView.builder(
itemCount: data.dataMessage.length,
shrinkWrap: true,
padding: EdgeInsets.only(top: 10, bottom: 10),
//physics: NeverScrollableScrollPhysics(),
itemBuilder: (context, m) {
return Container(
padding: EdgeInsets.only(
left: 14, right: 14, top: 10, bottom: 10),
child: Align(
alignment: (data.dataMessage[m].sender == "bank"
? Alignment.topLeft
: Alignment.topRight),
child: Container(
decoration: BoxDecoration(
borderRadius: BorderRadius.circular(20),
color: (data.dataMessage[m].sender == "bank"
? Colors.grey.shade200
: Colors.blue[200]),
),
padding: EdgeInsets.all(16),
child: ListTile(
title: Text('${data.dataMessage[m].message}',
style: TextStyle(
fontSize: 14, color: Colors.black),
textAlign: TextAlign.left),
subtitle: Text(
'${data.dataMessage[m].createdAt}',
style: TextStyle(color: Colors.grey[700]),
textAlign: TextAlign.left),
),
),
),
);
},
);
},
);
},
),
),
Align(
alignment: Alignment.bottomLeft,
child: Container(
padding: EdgeInsets.only(left: 10, bottom: 10, top: 10),
height: 60,
width: double.infinity,
color: Colors.white,
child: Form(
key: _formKey,
child: Row(
children: <Widget>[
Expanded(
child: TextFormField(
onSaved: (value) => message = value,
decoration: InputDecoration(
hintText: "Write something...",
hintStyle: TextStyle(color: Colors.black54),
border: InputBorder.none),
validator: (value) =>
value.isEmpty ? "Required" : null,
),
),
SizedBox(
width: 15,
),
FloatingActionButton(
onPressed: () {
send();
},
child: Icon(
Icons.send,
color: Colors.white,
size: 18,
),
backgroundColor: Colors.blue,
elevation: 0,
),
],
),
),
),
),
],
),
);
}
}
我的提供商：
// Store Message
Future<Map<String, dynamic>> storeMessage(String message) async {
String myId = await getId();
final url = ApiUrl.customerMessageStore;
print(url);
print(message);
final response = await http
.post(Uri.parse(url), body: {'customer_id': myId, 'message': message});
print('Response code: ${response.statusCode}');
final result = json.decode(response.body);
var dataResponse;
if (response.statusCode == 201) {
notifyListeners();
dataResponse = {
'type': 'success',
'title': 'Sent',
'message': result['message']
};
return dataResponse;
}
dataResponse = {
'type': 'error',
'title': 'Failed',
'message': 'Server Error di Provider'
};
return dataResponse;
}
命令提示符控制台：
E/flutter ( 4700): Tried calling: owner
E/flutter ( 4700): #0 Object.noSuchMethod (dart:core-patch/object_patch.dart:54:5)
E/flutter ( 4700): #1 Provider.of (package:provider/src/provider.dart:265:15)
E/flutter ( 4700): #2 MainScreen4.send (package:trashbank/pages/screens.dart:401:14)
E/flutter ( 4700): #3 MainScreen4.build.<anonymous closure> (package:trashbank/pages/screens.dart:507:25)
E/flutter ( 4700): #4 _InkResponseState._handleTap (package:flutter/src/material/ink_well.dart:994:20)
E/flutter ( 4700): #5 GestureRecognizer.invokeCallback (package:flutter/src/gestures/recognizer.dart:182:24)
E/flutter ( 4700): #6 TapGestureRecognizer.handleTapUp (package:flutter/src/gestures/tap.dart:607:11)
E/flutter ( 4700): #7 BaseTapGestureRecognizer._checkUp (package:flutter/src/gestures/tap.dart:296:5)
E/flutter ( 4700): #8 BaseTapGestureRecognizer.handlePrimaryPointer (package:flutter/src/gestures/tap.dart:230:7)
E/flutter ( 4700): #9 PrimaryPointerGestureRecognizer.handleEvent (package:flutter/src/gestures/recognizer.dart:475:9)
E/flutter ( 4700): #10 PointerRouter._dispatch (package:flutter/src/gestures/pointer_router.dart:93:12)
E/flutter ( 4700): #11 PointerRouter._dispatchEventToRoutes.<anonymous closure> (package:flutter/src/gestures/pointer_router.dart:138:9)
E/flutter ( 4700): #12 _LinkedHashMapMixin.forEach (dart:collection-patch/compact_hash.dart:397:8)
E/flutter ( 4700): #13 PointerRouter._dispatchEventToRoutes (package:flutter/src/gestures/pointer_router.dart:136:18)
E/flutter ( 4700): #14 PointerRouter.route (package:flutter/src/gestures/pointer_router.dart:122:7)
E/flutter ( 4700): #15 GestureBinding.handleEvent (package:flutter/src/gestures/binding.dart:439:19)
E/flutter ( 4700): #16 GestureBinding.dispatchEvent (package:flutter/src/gestures/binding.dart:419:22)
E/flutter ( 4700): #17 RendererBinding.dispatchEvent (package:flutter/src/rendering/binding.dart:288:11)
E/flutter ( 4700): #18 GestureBinding._handlePointerEventImmediately (package:flutter/src/gestures/binding.dart:374:7)
E/flutter ( 4700): #19 GestureBinding.handlePointerEvent (package:flutter/src/gestures/binding.dart:338:5)
E/flutter ( 4700): #20 GestureBinding._flushPointerEventQueue (package:flutter/src/gestures/binding.dart:296:7)
E/flutter ( 4700): #21 GestureBinding._handlePointerDataPacket (package:flutter/src/gestures/binding.dart:279:7)
E/flutter ( 4700): #22 _rootRunUnary (dart:async/zone.dart:1370:13)
E/flutter ( 4700): #23 _CustomZone.runUnary (dart:async/zone.dart:1265:19)
E/flutter ( 4700): #24 _CustomZone.runUnaryGuarded (dart:async/zone.dart:1170:7)
E/flutter ( 4700): #25 _invoke1 (dart:ui/hooks.dart:186:10)
E/flutter ( 4700): #26 PlatformDispatcher._dispatchPointerDataPacket (dart:ui/platform_dispatcher.dart:282:7)
E/flutter ( 4700): #27 _dispatchPointerDataPacket (dart:ui/hooks.dart:96:31)
我不明白“所有者”是什么意思。请帮助它运行良好。谢谢。
答案 0 :(得分：0)
你有这个代码：
BuildContext context;
Future<void> send() async {
_formKey.currentState.save();
print("field: $message");
Provider.of<SavingProvider>(context, listen: false)
.storeMessage(message)
.then((res) {
但是您的变量 context 未初始化。您可以在 send() 方法中移动 build 函数，或者在 context 方法中初始化变量 build，例如
Widget build(BuildContext ctx) {
context = ctx;
或者您可以将上下文作为参数传递给 send 方法 - 这是我的首选方法：
Future<void> send(BuildContext context) async {
错误信息：
E/flutter ( 4700): Tried calling: owner
E/flutter ( 4700): #0 Object.noSuchMethod (dart:core-patch/object_patch.dart:54:5)
E/flutter ( 4700): #1 Provider.of (package:provider/src/provider.dart:265:15)
告诉您在文件 provider.dart 的第 265 行，方法 Provider.of 调用了一个未找到的方法 owner。查看源代码，您将看到它指的是 context.owner。问题是 context 为空。