我想创建一个应用程序，其 UI 可以根据设备方向进行更新。在肖像布局中，我使用抽屉来显示一些元素（Fig. https://i.stack.imgur.com/1M9hc.png）。在横向布局中，没有抽屉，但元素显示在屏幕左侧的列中（Fig. https://i.stack.imgur.com/6g4yW.png）。当抽屉关闭时，程序就会运行。
但是当我在抽屉打开的情况下将方向从纵向切换为横向，我收到错误“当小部件树被锁定时调用 setState() 或 markNeedsBuild()”
堆栈提供以下信息：
Built build\app\outputs\apk\debug\app-debug.apk.
I/FlutterActivityDelegate(28527): onResume setting current activity to this
I/flutter (28527): PORTRAIT LAYOUT!!!!!!!!!!!!!!!!!!!!!!
I/hwaps (28527): JNI_OnLoad
I/flutter (28527): LANDSCAPE LAYOUT!!!!!!!!!!!!!!!!!!!!!!
I/flutter (28527): ══╡ EXCEPTION CAUGHT BY WIDGETS LIBRARY ╞═══════════════════════════════════════════════════════════
I/flutter (28527): The following assertion was thrown while finalizing the widget tree:
I/flutter (28527): setState() or markNeedsBuild() called when widget tree was locked.
I/flutter (28527): This _ModalScope<dynamic> widget cannot be marked as needing to build because the framework is
I/flutter (28527): locked.
I/flutter (28527): The widget on which setState() or markNeedsBuild() was called was:
I/flutter (28527): _ModalScope<dynamic>-[LabeledGlobalKey<_ModalScopeState<dynamic>>#e1f0f](state:
I/flutter (28527): _ModalScopeState<dynamic>#830e3)
I/flutter (28527):
I/flutter (28527): When the exception was thrown, this was the stack:
I/flutter (28527): #0 Element.markNeedsBuild.<anonymous closure> (package:flutter/src/widgets/framework.dart:3453:9)
I/flutter (28527): #1 Element.markNeedsBuild (package:flutter/src/widgets/framework.dart:3462:6)
I/flutter (28527): #2 State.setState (package:flutter/src/widgets/framework.dart:1141:14)
I/flutter (28527): #3 _ModalScopeState._routeSetState (package:flutter/src/widgets/routes.dart:464:5)
I/flutter (28527): #4 ModalRoute.setState (package:flutter/src/widgets/routes.dart:562:30)
I/flutter (28527): #5 ModalRoute.changedInternalState (package:flutter/src/widgets/routes.dart:1018:5)
I/flutter (28527): #6 _ModalRoute&TransitionRoute&LocalHistoryRoute.removeLocalHistoryEntry (package:flutter/src/widgets/routes.dart:348:7)
I/flutter (28527): #7 LocalHistoryEntry.remove (package:flutter/src/widgets/routes.dart:296:12)
I/flutter (28527): #8 DrawerControllerState.dispose (package:flutter/src/material/drawer.dart:201:20)
I/flutter (28527): #9 StatefulElement.unmount (package:flutter/src/widgets/framework.dart:3821:12)
I/flutter (28527): #10 _InactiveElements._unmount (package:flutter/src/widgets/framework.dart:1697:13)
I/flutter (28527): #11 _InactiveElements._unmount.<anonymous closure> (package:flutter/src/widgets/framework.dart:1695:7)
I/flutter (28527): #12 ComponentElement.visitChildren (package:flutter/src/widgets/framework.dart:3676:14)
I/flutter (28527): #13 _InactiveElements._unmount (package:flutter/src/widgets/framework.dart:1693:13)
I/flutter (28527): #14 _InactiveElements._unmount.<anonymous closure> (package:flutter/src/widgets/framework.dart:1695:7)
I/flutter (28527): #15 ComponentElement.visitChildren (package:flutter/src/widgets/framework.dart:3676:14)
I/flutter (28527): #16 _InactiveElements._unmount (package:flutter/src/widgets/framework.dart:1693:13)
I/flutter (28527): #17 ListIterable.forEach (dart:_internal/iterable.dart:39:13)
I/flutter (28527): #18 _InactiveElements._unmountAll (package:flutter/src/widgets/framework.dart:1706:25)
I/flutter (28527): #19 BuildOwner.finalizeTree.<anonymous closure> (package:flutter/src/widgets/framework.dart:2328:27)
I/flutter (28527): #20 BuildOwner.lockState (package:flutter/src/widgets/framework.dart:2160:15)
I/flutter (28527): #21 BuildOwner.finalizeTree (package:flutter/src/widgets/framework.dart:2327:7)
I/flutter (28527): #22 _WidgetsFlutterBinding&BindingBase&GestureBinding&ServicesBinding&SchedulerBinding&PaintingBinding&RendererBinding&WidgetsBinding.drawFrame (package:flutter/src/widgets/binding.dart:628:18)
I/flutter (28527): #23 _WidgetsFlutterBinding&BindingBase&GestureBinding&ServicesBinding&SchedulerBinding&PaintingBinding&RendererBinding._handlePersistentFrameCallback (package:flutter/src/rendering/binding.dart:208:5)
I/flutter (28527): #24 _WidgetsFlutterBinding&BindingBase&GestureBinding&ServicesBinding&SchedulerBinding._invokeFrameCallback (package:flutter/src/scheduler/binding.dart:990:15)
I/flutter (28527): #25 _WidgetsFlutterBinding&BindingBase&GestureBinding&ServicesBinding&SchedulerBinding.handleDrawFrame (package:flutter/src/scheduler/binding.dart:930:9)
I/flutter (28527): #26 _WidgetsFlutterBinding&BindingBase&GestureBinding&ServicesBinding&SchedulerBinding._handleDrawFrame (package:flutter/src/scheduler/binding.dart:842:5)
I/flutter (28527): #27 _invoke (dart:ui/hooks.dart:120:13)
I/flutter (28527): #28 _drawFrame (dart:ui/hooks.dart:109:3)
I/flutter (28527): ════════════════════════════════════════════════════════════════════════════════════════════════════
I/flutter (28527): Another exception was thrown: 'package:flutter/src/widgets/framework.dart': Failed assertion: line 3424 pos 12: '_debugLifecycleState != _ElementLifecycle.defunct': is not true.
I/flutter (28527): Another exception was thrown: 'package:flutter/src/widgets/framework.dart': Failed assertion: line 3424 pos 12: '_debugLifecycleState != _ElementLifecycle.defunct': is not true.
I/flutter (28527): Another exception was thrown: 'package:flutter/src/widgets/framework.dart': Failed assertion: line 3424 pos 12: '_debugLifecycleState != _ElementLifecycle.defunct': is not true.
I/flutter (28527): Another exception was thrown: 'package:flutter/src/widgets/framework.dart': Failed assertion: line 3424 pos 12: '_debugLifecycleState != _ElementLifecycle.defunct': is not true.
I/flutter (28527): Another exception was thrown: 'package:flutter/src/widgets/framework.dart': Failed assertion: line 3424 pos 12: '_debugLifecycleState != _ElementLifecycle.defunct': is not true.
I/flutter (28527): Another exception was thrown: 'package:flutter/src/widgets/framework.dart': Failed assertion: line 3424 pos 12: '_debugLifecycleState != _ElementLifecycle.defunct': is not true.
I/flutter (28527): Another exception was thrown: 'package:flutter/src/widgets/framework.dart': Failed assertion: line 3424 pos 12: '_debugLifecycleState != _ElementLifecycle.defunct': is not true.
I/flutter (28527): Another exception was thrown: 'package:flutter/src/widgets/framework.dart': Failed assertion: line 3424 pos 12: '_debugLifecycleState != _ElementLifecycle.defunct': is not true.
I/flutter (28527): Another exception was thrown: 'package:flutter/src/widgets/framework.dart': Failed assertion: line 3424 pos 12: '_debugLifecycleState != _ElementLifecycle.defunct': is not true.
I/flutter (28527): Another exception was thrown: 'package:flutter/src/widgets/framework.dart': Failed assertion: line 3424 pos 12: '_debugLifecycleState != _ElementLifecycle.defunct': is not true.
我在 Appbar 的开头有一个返回按钮（Fig. https://i.stack.imgur.com/KJrV2.png).
这是我的代码：
import 'package:flutter/material.dart';
void main() => runApp(new MyApp());
class MyApp extends StatefulWidget {
@override
_MyAppState createState() => _MyAppState();
}
class _MyAppState extends State<MyApp> {
@override
Widget build(BuildContext context) {
return new MaterialApp(
title: 'demo',
theme: new ThemeData(primarySwatch: Colors.blue),
home: new Home(),
);
}
}
class Home extends StatefulWidget {
@override
_HomeState createState() => _HomeState();
}
class _HomeState extends State<Home> {
static const int SCREEN_WIDTH_MIN = 600;
@override
Widget build(BuildContext context) {
Widget _homelayout;
var screenWidth = MediaQuery.of(context).size.width;
var screenOrientation = MediaQuery.of(context).orientation;
if ((screenWidth > SCREEN_WIDTH_MIN) &&
(screenOrientation == Orientation.landscape)) {
print('LANDSCAPE LAYOUT!!!!!!!!!!!!!!!!!!!!!!');
//_homelayout = _buildLandscapeLayout(context);
_homelayout = _buildLandscapeLayout();
} else {
print('PORTRAIT LAYOUT!!!!!!!!!!!!!!!!!!!!!!');
_homelayout = _buildPortraitLayout();
}
return _homelayout;
}
Widget _buildPortraitLayout() {
return new Scaffold(
appBar: new AppBar(
title: new Text('demo'),
),
drawer: new DeviceListDrawer(),
body: new Center(
child: new Text('body'),
),
);
}
}
Widget _buildLandscapeLayout() {
return new Scaffold(
appBar: new AppBar(
title: new Text('demo'),
),
body: new Center(
child: new Row(
children: <Widget>[
new DeviceListDrawer(),
new Text('body')
],
),
),
);
}
class DeviceListDrawer extends StatefulWidget {
@override
_DeviceListDrawerState createState() => _DeviceListDrawerState();
}
class _DeviceListDrawerState extends State<DeviceListDrawer> {
@override
Widget build(BuildContext context) {
return new Container(
width: 200.0,
color: Colors.white,
child: Column(
children: <Widget>[
new Container(
width: 200.0,
color: Colors.blue,
padding: new EdgeInsets.only(
top: MediaQuery.of(context).padding.top + 16.0, bottom: 16.0),
child: new Text('demo '),
),
new Expanded(
child: new ListView(
children: <Widget>[
new Text('item 1'),
new Text('item 2'),
new Text('item 3'),
],
),
),
new RaisedButton(
child: new Text('add item'),
onPressed: () {},
)
],
),
);
}
}
您能指出是什么问题吗？我怎样才能使布局动态化？感谢您的帮助。
