Xamarin Forms iOS页面强制特定屏幕方向适配问题（iOS16+）

在Xamarin Forms应用中，部分页面需要根据内容切换横竖屏，Android端实现无问题，但iOS 16移除了旧的UIDevice.SetValueForKey设置方向的方法，原MessagingCenter方案失效。以下是适配iOS 16+的完整实现步骤：

1. 定义共享接口 #

在共享项目中创建屏幕方向服务接口：

namespace MyApp
{
    public interface IScreenOrientationService
    {
        void ForcePortrait();
        void ForceLandscape();
        void ResetToDefault();
    }
}

2. iOS平台实现依赖服务 #

在iOS项目中实现该接口，适配iOS 16+的新API，同时兼容旧版本：

[assembly: Xamarin.Forms.Dependency(typeof(MyApp.iOS.ScreenOrientationService))]
namespace MyApp.iOS
{
    public class ScreenOrientationService : IScreenOrientationService
    {
        private UIInterfaceOrientationMask _defaultOrientationMask;

        public ScreenOrientationService()
        {
            // 保存应用默认支持的方向掩码
            _defaultOrientationMask = UIApplication.SharedApplication.SupportedInterfaceOrientationsForWindow(UIApplication.SharedApplication.KeyWindow);
        }

        public void ForcePortrait()
        {
            UpdateOrientation(UIInterfaceOrientationMask.Portrait);
        }

        public void ForceLandscape()
        {
            // 根据需求选择LandscapeLeft/LandscapeRight或同时支持
            UpdateOrientation(UIInterfaceOrientationMask.LandscapeLeft | UIInterfaceOrientationMask.LandscapeRight);
        }

        public void ResetToDefault()
        {
            UpdateOrientation(_defaultOrientationMask);
        }

        private void UpdateOrientation(UIInterfaceOrientationMask targetMask)
        {
            if (UIDevice.CurrentDevice.CheckSystemVersion(16, 0))
            {
                // 获取当前活跃的窗口场景
                var windowScene = UIApplication.SharedApplication.ConnectedScenes
                    .OfType<UIWindowScene>()
                    .FirstOrDefault(scene => scene.ActivationState == UISceneActivationState.ForegroundActive);

                if (windowScene != null)
                {
                    // 更新根视图控制器支持的方向
                    var rootVC = UIApplication.SharedApplication.KeyWindow?.RootViewController;
                    if (rootVC != null)
                    {
                        // 自定义根视图控制器的支持方向（需要子类化UINavigationController）
                        if (rootVC is CustomNavigationController navVC)
                        {
                            navVC.TargetOrientationMask = targetMask;
                            navVC.SetNeedsUpdateOfSupportedInterfaceOrientations();
                        }

                        // 请求窗口场景更新几何布局
                        var preferences = new UIWindowSceneGeometryPreferencesIOS(targetMask);
                        windowScene.RequestGeometryUpdate(preferences, error =>
                        {
                            if (error != null)
                            {
                                Console.WriteLine($"Orientation update error: {error.LocalizedDescription}");
                            }
                        });
                    }
                }
            }
            else
            {
                // iOS 16以下的旧实现
                UIInterfaceOrientation targetOrientation = UIInterfaceOrientation.Portrait;
                if (targetMask.HasFlag(UIInterfaceOrientationMask.LandscapeLeft))
                {
                    targetOrientation = UIInterfaceOrientation.LandscapeLeft;
                }
                else if (targetMask.HasFlag(UIInterfaceOrientationMask.LandscapeRight))
                {
                    targetOrientation = UIInterfaceOrientation.LandscapeRight;
                }

                UIDevice.CurrentDevice.SetValueForKey(NSNumber.FromInt32((int)targetOrientation), new NSString("orientation"));
            }
        }
    }

    // 子类化导航控制器，动态返回支持的方向
    public class CustomNavigationController : UINavigationController
    {
        public UIInterfaceOrientationMask TargetOrientationMask { get; set; } = UIInterfaceOrientationMask.AllButUpsideDown;

        public override UIInterfaceOrientationMask GetSupportedInterfaceOrientations()
        {
            return TargetOrientationMask;
        }
    }
}

3. 配置iOS项目的根视图控制器 #

在AppDelegate中，将默认的导航控制器替换为自定义的CustomNavigationController：

[Register("AppDelegate")]
public partial class AppDelegate : global::Xamarin.Forms.Platform.iOS.FormsApplicationDelegate
{
    public override bool FinishedLaunching(UIApplication app, NSDictionary options)
    {
        global::Xamarin.Forms.Forms.Init();
        LoadApplication(new App());

        // 替换根视图控制器为自定义导航控制器
        var rootVC = new CustomNavigationController(Window.RootViewController);
        Window.RootViewController = rootVC;

        return base.FinishedLaunching(app, options);
    }
}

4. 在页面中调用方向控制 #

在需要指定方向的页面的OnAppearing和OnDisappearing方法中调用服务：

protected override void OnAppearing()
{
    base.OnAppearing();
    // 强制横屏
    DependencyService.Get<IScreenOrientationService>().ForceLandscape();
}

protected override void OnDisappearing()
{
    base.OnDisappearing();
    // 恢复默认方向
    DependencyService.Get<IScreenOrientationService>().ResetToDefault();
}

5. 配置Info.plist #

确保Info.plist中包含应用需要支持的所有屏幕方向，否则强制方向会失效：

<key>UISupportedInterfaceOrientations</key>
<array>
    <string>UIInterfaceOrientationPortrait</string>
    <string>UIInterfaceOrientationLandscapeLeft</string>
    <string>UIInterfaceOrientationLandscapeRight</string>
</array>
<key>UISupportedInterfaceOrientations~ipad</key>
<array>
    <string>UIInterfaceOrientationPortrait</string>
    <string>UIInterfaceOrientationPortraitUpsideDown</string>
    <string>UIInterfaceOrientationLandscapeLeft</string>
    <string>UIInterfaceOrientationLandscapeRight</string>
</array>

内容的提问来源于stack exchange，提问作者Riley Houston