应为 'Map<String, dynamic>' 类型的值，但得到了 'Null' 类型的值
Expected a value of type 'Map<String, dynamic>', but got one of type 'Null'
我正在使用 flutter 并通过 cloud_firestore 管理数据。
我可以将数据发送到 firestore，但现在我正在努力读取数据。
在firestore中，数据是这样存储的；
"users" collection -> "(uid)" document -> "userName" string field
这是我正在尝试的代码。
显示 LinerProgressIndicator 直到快照完成。
CollectionReference users = FirebaseFirestore.instance.collection('users');
FutureBuilder(
future: users.doc().get(),
builder: (context, AsyncSnapshot<DocumentSnapshot> snapshot) {
if (snapshot.connectionState != ConnectionState.done) {
return const SizedBox(
width: 50,
child: LinearProgressIndicator(),
);
}
if (snapshot.hasError) {
return SelectableText(snapshot.error.toString());
}
if (!snapshot.hasData) {
return const Text('No data found');
}
Map<String, dynamic> data =
snapshot.data!.data() as Map<String, dynamic>;
return Text("User Name: ${data['userName']}");
},
)
但是当快照完成时，发生了错误。
Expected a value of type 'Map<String, dynamic>', but got one of type
'Null'
我引用了一次性阅读项this official article
我已经确认 'users' -> uid -> 'userName' 的值是正确的。
加法 1：
我调试了 FutureBuilder 的 builder。
print('${snapshot.data!.data()}');
null
print('${snapshot.data}');
Instance of '_JsonDocumentSnapshot'
加法 2：
@Saiful Islam
我重写了代码。
然后出现其他错误。
Expected a value of type 'Map<String, dynamic>', but got one of type '_JsonDocumentSnapshot'
此外，print() 结果与加法 1 相同。
测试代码；
CollectionReference users = FirebaseFirestore.instance.collection('users');
FutureBuilder(
future: users.doc(FirebaseAuth.instance.currentUser!.uid).get(),
builder: (context, AsyncSnapshot<DocumentSnapshot> snapshot) {
print('${snapshot.data!.data()}'); //null
print('${snapshot.data}'); //Instance of '_JsonDocumentSnapshot'
if (snapshot.connectionState != ConnectionState.done) {
return const SizedBox(
width: 50,
child: LinearProgressIndicator(),
);
}
if (snapshot.hasError) {
return SelectableText(snapshot.error.toString());
}
if (!snapshot.hasData) {
return const Text('No data found');
}
if (snapshot.connectionState == ConnectionState.done) {
Map<String, dynamic> data =
snapshot.data as Map<String, dynamic>;
return Text("User Name: ${data['username']}");
}
return const SelectableText("userName");
},
)
加法 3：##
已添加 print('${jsonDecode(snapshot.data)}')。
再次出现错误。
Bad state: cannot get a field on a DocumentSnapshotPlatform which does
not exist
错误详情；
Launching lib\main.dart on Chrome in debug mode...
This app is linked to the debug service: ws://127.0.0.1:59027/fBobSNPxOzo%3D/ws
Debug service listening on ws://127.0.0.1:59027/fBobSNPxOzo=/ws
Running with sound null safety
Connecting to VM Service at ws://127.0.0.1:59027/fBobSNPxOzo=/ws
════════ Exception caught by widgets library ═══════════════════════════════════
The following StateError was thrown building FutureBuilder<DocumentSnapshot<Object?>>(dirty, state: _FutureBuilderState<DocumentSnapshot<Object?>>#330c8):
Bad state: cannot get a field on a DocumentSnapshotPlatform which does not exist
The relevant error-causing widget was
FutureBuilder<DocumentSnapshot<Object?>> FutureBuilder:file:///D:/FlutterProjects/testProject/lib/profile.dart:32:13
When the exception was thrown, this was the stack
C:/b/s/w/ir/cache/builder/src/out/host_debug/dart-sdk/lib/_internal/js_dev_runtime/private/ddc_runtime/errors.dart 251:49 throw_
packages/cloud_firestore_platform_interface/src/platform_interface/platform_interface_document_snapshot.dart 77:7 get
packages/cloud_firestore/src/document_snapshot.dart 92:48 get
packages/cloud_firestore/src/document_snapshot.dart 96:40 _get
packages/testProject/profile.dart 50:45 <fn>
packages/flutter/src/widgets/async.dart 782:48 build
packages/flutter/src/widgets/framework.dart 4782:27 build
packages/flutter/src/widgets/framework.dart 4665:15 performRebuild
packages/flutter/src/widgets/framework.dart 4840:11 performRebuild
packages/flutter/src/widgets/framework.dart 4355:5 rebuild
packages/flutter/src/widgets/framework.dart 2620:31 buildScope
packages/flutter/src/widgets/binding.dart 882:9 drawFrame
packages/flutter/src/rendering/binding.dart 319:5 [_handlePersistentFrameCallback]
packages/flutter/src/scheduler/binding.dart 1143:15 [_invokeFrameCallback]
packages/flutter/src/scheduler/binding.dart 1080:9 handleDrawFrame
packages/flutter/src/scheduler/binding.dart 996:5 [_handleDrawFrame]
C:/b/s/w/ir/cache/builder/src/out/host_debug/flutter_web_sdk/lib/_engine/engine/platform_dispatcher.dart 1003:13 invoke
C:/b/s/w/ir/cache/builder/src/out/host_debug/flutter_web_sdk/lib/_engine/engine/platform_dispatcher.dart 157:5 invokeOnDrawFrame
C:/b/s/w/ir/cache/builder/src/out/host_debug/flutter_web_sdk/lib/_engine/engine.dart 440:45 <fn>
════════════════════════════════════════════════════════════════════════════════
════════ Exception caught by rendering library ═════════════════════════════════
A RenderFlex overflowed by 99340 pixels on the bottom.
The relevant error-causing widget was
Column Column:file:///D:/FlutterProjects/testProject/lib/profile.dart:26:20
════════════════════════════════════════════════════════════════════════════════
你能想到什么样的问题？
谢谢。
你应该只return文件的地图存在。但是，您没有检查此条件是否为真。
为了安全起见，不要 return 数据，除非它在 if 语句中，该语句检查 hasData 然后 exists.
错误也可能是由于拼写错误造成的。再次仔细检查。
但是你的错误是从一开始就出现的，这一行：
future: users.doc().get(),
你没有说是哪个文件。当你运行这个查询时，你需要传递文档的id。
future: users.doc('0Cb43453fdsg4').get(), //This is an example 'id'.
我正在使用 flutter 并通过 cloud_firestore 管理数据。 我可以将数据发送到 firestore，但现在我正在努力读取数据。
在firestore中，数据是这样存储的；
"users" collection -> "(uid)" document -> "userName" string field
这是我正在尝试的代码。 显示 LinerProgressIndicator 直到快照完成。
CollectionReference users = FirebaseFirestore.instance.collection('users');
FutureBuilder(
future: users.doc().get(),
builder: (context, AsyncSnapshot<DocumentSnapshot> snapshot) {
if (snapshot.connectionState != ConnectionState.done) {
return const SizedBox(
width: 50,
child: LinearProgressIndicator(),
);
}
if (snapshot.hasError) {
return SelectableText(snapshot.error.toString());
}
if (!snapshot.hasData) {
return const Text('No data found');
}
Map<String, dynamic> data =
snapshot.data!.data() as Map<String, dynamic>;
return Text("User Name: ${data['userName']}");
},
)
但是当快照完成时，发生了错误。
Expected a value of type 'Map<String, dynamic>', but got one of type 'Null'
我引用了一次性阅读项this official article
我已经确认 'users' -> uid -> 'userName' 的值是正确的。
加法 1：
我调试了 FutureBuilder 的 builder。
print('${snapshot.data!.data()}');
null
print('${snapshot.data}');
Instance of '_JsonDocumentSnapshot'
加法 2：
@Saiful Islam
我重写了代码。 然后出现其他错误。
Expected a value of type 'Map<String, dynamic>', but got one of type '_JsonDocumentSnapshot'
此外，print() 结果与加法 1 相同。
测试代码；
CollectionReference users = FirebaseFirestore.instance.collection('users');
FutureBuilder(
future: users.doc(FirebaseAuth.instance.currentUser!.uid).get(),
builder: (context, AsyncSnapshot<DocumentSnapshot> snapshot) {
print('${snapshot.data!.data()}'); //null
print('${snapshot.data}'); //Instance of '_JsonDocumentSnapshot'
if (snapshot.connectionState != ConnectionState.done) {
return const SizedBox(
width: 50,
child: LinearProgressIndicator(),
);
}
if (snapshot.hasError) {
return SelectableText(snapshot.error.toString());
}
if (!snapshot.hasData) {
return const Text('No data found');
}
if (snapshot.connectionState == ConnectionState.done) {
Map<String, dynamic> data =
snapshot.data as Map<String, dynamic>;
return Text("User Name: ${data['username']}");
}
return const SelectableText("userName");
},
)
加法 3：##
已添加 print('${jsonDecode(snapshot.data)}')。
再次出现错误。
Bad state: cannot get a field on a DocumentSnapshotPlatform which does not exist
错误详情；
Launching lib\main.dart on Chrome in debug mode...
This app is linked to the debug service: ws://127.0.0.1:59027/fBobSNPxOzo%3D/ws
Debug service listening on ws://127.0.0.1:59027/fBobSNPxOzo=/ws
Running with sound null safety
Connecting to VM Service at ws://127.0.0.1:59027/fBobSNPxOzo=/ws
════════ Exception caught by widgets library ═══════════════════════════════════
The following StateError was thrown building FutureBuilder<DocumentSnapshot<Object?>>(dirty, state: _FutureBuilderState<DocumentSnapshot<Object?>>#330c8):
Bad state: cannot get a field on a DocumentSnapshotPlatform which does not exist
The relevant error-causing widget was
FutureBuilder<DocumentSnapshot<Object?>> FutureBuilder:file:///D:/FlutterProjects/testProject/lib/profile.dart:32:13
When the exception was thrown, this was the stack
C:/b/s/w/ir/cache/builder/src/out/host_debug/dart-sdk/lib/_internal/js_dev_runtime/private/ddc_runtime/errors.dart 251:49 throw_
packages/cloud_firestore_platform_interface/src/platform_interface/platform_interface_document_snapshot.dart 77:7 get
packages/cloud_firestore/src/document_snapshot.dart 92:48 get
packages/cloud_firestore/src/document_snapshot.dart 96:40 _get
packages/testProject/profile.dart 50:45 <fn>
packages/flutter/src/widgets/async.dart 782:48 build
packages/flutter/src/widgets/framework.dart 4782:27 build
packages/flutter/src/widgets/framework.dart 4665:15 performRebuild
packages/flutter/src/widgets/framework.dart 4840:11 performRebuild
packages/flutter/src/widgets/framework.dart 4355:5 rebuild
packages/flutter/src/widgets/framework.dart 2620:31 buildScope
packages/flutter/src/widgets/binding.dart 882:9 drawFrame
packages/flutter/src/rendering/binding.dart 319:5 [_handlePersistentFrameCallback]
packages/flutter/src/scheduler/binding.dart 1143:15 [_invokeFrameCallback]
packages/flutter/src/scheduler/binding.dart 1080:9 handleDrawFrame
packages/flutter/src/scheduler/binding.dart 996:5 [_handleDrawFrame]
C:/b/s/w/ir/cache/builder/src/out/host_debug/flutter_web_sdk/lib/_engine/engine/platform_dispatcher.dart 1003:13 invoke
C:/b/s/w/ir/cache/builder/src/out/host_debug/flutter_web_sdk/lib/_engine/engine/platform_dispatcher.dart 157:5 invokeOnDrawFrame
C:/b/s/w/ir/cache/builder/src/out/host_debug/flutter_web_sdk/lib/_engine/engine.dart 440:45 <fn>
════════════════════════════════════════════════════════════════════════════════
════════ Exception caught by rendering library ═════════════════════════════════
A RenderFlex overflowed by 99340 pixels on the bottom.
The relevant error-causing widget was
Column Column:file:///D:/FlutterProjects/testProject/lib/profile.dart:26:20
════════════════════════════════════════════════════════════════════════════════
你能想到什么样的问题？
谢谢。
你应该只return文件的地图存在。但是，您没有检查此条件是否为真。
为了安全起见，不要 return 数据，除非它在 if 语句中，该语句检查 hasData 然后 exists.
错误也可能是由于拼写错误造成的。再次仔细检查。
但是你的错误是从一开始就出现的，这一行：
future: users.doc().get(),
你没有说是哪个文件。当你运行这个查询时，你需要传递文档的id。
future: users.doc('0Cb43453fdsg4').get(), //This is an example 'id'.