Flutter：如何按需设置和锁定屏幕方向

在我的第一页上，我需要将屏幕设置为横向模式并锁定它，以使其不能旋转到纵向模式，而只能在一页上旋转。因此需要一种即时启用此功能的方法。有人知道怎么做吗？

我希望它可以向左旋转风景或向右旋转风景，只是不进入纵向模式。

首先导入服务包：

import 'package:flutter/services.dart';

这将使您可以访问该SystemChrome课程，"Controls specific aspects of the operating system's graphical interface and how it interacts with the application."

加载小部件时，请执行以下操作：

@override
void initState(){
  super.initState();
  SystemChrome.setPreferredOrientations([
      DeviceOrientation.landscapeRight,
      DeviceOrientation.landscapeLeft,
  ]);
}

然后当我离开页面时，将其恢复为正常状态，如下所示：

@override
dispose(){
  SystemChrome.setPreferredOrientations([
    DeviceOrientation.landscapeRight,
    DeviceOrientation.landscapeLeft,
    DeviceOrientation.portraitUp,
    DeviceOrientation.portraitDown,
  ]);
  super.dispose();
}

我将使用一个简单的mixin将手机锁定为纵向模式。以下解决方案将整个应用程序锁定为纵向模式，或将特定屏幕设置为纵向模式，同时保持旋转状态。

import 'package:flutter/cupertino.dart';
import 'package:flutter/services.dart';

/// Forces portrait-only mode application-wide
/// Use this Mixin on the main app widget i.e. app.dart
/// Flutter's 'App' has to extend Stateless widget.
///
/// Call `super.build(context)` in the main build() method
/// to enable portrait only mode
mixin PortraitModeMixin on StatelessWidget {
  @override
  Widget build(BuildContext context) {
    _portraitModeOnly();
    return null;
  }
}

/// Forces portrait-only mode on a specific screen
/// Use this Mixin in the specific screen you want to
/// block to portrait only mode.
///
/// Call `super.build(context)` in the State's build() method
/// and `super.dispose();` in the State's dispose() method
mixin PortraitStatefulModeMixin<T extends StatefulWidget> on State<T> {
  @override
  Widget build(BuildContext context) {
    _portraitModeOnly();
    return null;
  }

  @override
  void dispose() {
    _enableRotation();
  }
}

/// blocks rotation; sets orientation to: portrait
void _portraitModeOnly() {
  SystemChrome.setPreferredOrientations([
    DeviceOrientation.portraitUp,
    DeviceOrientation.portraitDown,
  ]);
}

void _enableRotation() {
  SystemChrome.setPreferredOrientations([
    DeviceOrientation.portraitUp,
    DeviceOrientation.portraitDown,
    DeviceOrientation.landscapeLeft,
    DeviceOrientation.landscapeRight,
  ]);
}

要阻止整个应用PortraitModeMixin中的旋转，请在主App窗口小部件中实施。记得打电话super.build(context)的Widget build(BuildContext context)方法。

/// Main App widget
class App extends StatelessWidget with PortraitModeMixin {
  const App();

  @override
  Widget build(BuildContext context) {
    super.build(context);
    return CupertinoApp(
      title: 'Flutter Demo',
      theme: CupertinoThemeData(),
      home: Text("Block screen rotation example"),
    );
  }
}

为了阻止旋转在一个特定的屏幕落实PortraitStatefulModeMixin<SampleScreen>在具体的屏幕的状态。记住要调用super.build(context)State的build()方法和super.dispose()indispose()方法。如果您的屏幕是StatelessWidget-只需重复应用程序的解决方案（上一个示例），即使用PortraitModeMixin。

/// Specific screen
class SampleScreen extends StatefulWidget {
  SampleScreen() : super();

  @override
  State<StatefulWidget> createState() => _SampleScreenState();
}

class _SampleScreenState extends State<SampleScreen>
    with PortraitStatefulModeMixin<SampleScreen> {
  @override
  Widget build(BuildContext context) {
    super.build(context);
    return Text("Flutter - Block screen rotation example");
  }

  @override
  void dispose() {
     super.dispose();
  }
}

具有此类语法的Mixins从Dart 2.1开始工作

void main() {
  WidgetsFlutterBinding.ensureInitialized();
  SystemChrome.setPreferredOrientations([DeviceOrientation.portraitUp, DeviceOrientation.portraitDown])
    .then((_) {
      runApp(new MyApp());
    });
}

有时由于有关方向的空信息而无法使用。您可以像这样简单地使用它：

import services.dart


void main() {
    SystemChrome.setPreferredOrientations(
    [DeviceOrientation.portraitUp]
     )
        .then((_) {
          runApp(new MyApp());
        });
    }

//启动应用程序后等待设置屏幕方向，然后->然后锁定方向

导入services.dart，您的void main功能应类似于：

void main(){

    WidgetsFlutterBinding.ensureInitialized();
    SystemChrome.setPreferredOrientations(
       [DeviceOrientation.portraitUp, DeviceOrientation.portraitDown])
       .then((_){
           runApp(MyApp());
       }
    );
}

您可以为此https://pub.dev/packages/orientation_helper使用direction_helper。它的主要目标是为应用程序中的每个屏幕设置方向。

导入services.dart包并添加以下代码以将设备方向锁定为portraitUp模式：

 import 'package:flutter/services.dart';

 main() {
     WidgetsFlutterBinding.ensureInitialized();
     SystemChrome.setPreferredOrientations([DeviceOrientation.portraitUp]);
     runApp(MyHomePage());
 }