.NET MAUI添加OnboardingPage后Shell依赖注入导航异常求助

之前.NET MAUI应用的页面导航完全正常，添加OnboardingPage后出现一系列Shell相关错误，无论怎么修复都无法解决，频繁出现Shell.Current为空的情况。最近持续触发的错误为：

System.InvalidOperationException: 'Unable to resolve service for type Microsoft.Maui.Controls.Shell while attempting to activate App.Core.Services.NavigationServices'

已尝试的排查步骤 #

• 检查路由配置：
  • 确认OnboardingPage已在AppShell.xaml.cs的Routing.RegisterRoute()中正确注册
  • 反复核对路由名称，无拼写错误
  • 其他页面（HomePage、HistoryPage、GoalPage）的导航路由在添加引导页前运行正常
• 尝试延迟Shell初始化：
  • 在AppShell构造函数中使用Task.Delay(100)确保Shell先加载完成
  • 即使添加延迟，导航到引导页时Shell.Current仍为空
• 检查依赖注入（DI）配置：
  • 已将AppShell在MauiProgram.cs中注册为单例
  • 导航服务NavigationServices依赖于Shell，且添加引导页前DI配置正常
  • 错误依然存在，说明DI容器未正确解析Shell
• 强制解析Shell：
  • 在CreateWindow()中尝试用_serviceProvider.GetRequiredService<AppShell>()获取AppShell实例
  • 导航时仍出现空引用错误

当前困境 #

• 添加OnboardingPage前所有功能正常
• 现在因DI无法获取Shell导致导航完全失效
• 不清楚如何正确初始化Shell并确保其能被导航服务调用

相关代码 #

public partial class App : Application
{
    private readonly IServiceProvider _serviceProvider;

    public App(IServiceProvider serviceProvider)
    {
        InitializeComponent();
        _serviceProvider = serviceProvider;
    }

    protected override Window CreateWindow(IActivationState? activationState)
    {
        var shell = _serviceProvider.GetService<AppShell>();

        if (shell == null)
        {
            throw new InvalidOperationException("AppShell could not be resolved from service provider.");
        }

        bool hasCompletedOnboarding = PreferencesServices.HasCompletedOnboarding();

        // Navigate to the appropriate startup page inside the Shell
        Task.Run(async () =>
        {
            await Task.Delay(100); // Small delay to ensure Shell initializes
            await shell.GoToAsync(hasCompletedOnboarding ? "//home" : "//onboarding");
        });

        return new Window(shell);
    }
}

public AppShell()
{
    InitializeComponent();

    Routing.RegisterRoute("home", typeof(HomePage));
    Routing.RegisterRoute("onboarding", typeof(OnboardingPage));
    Routing.RegisterRoute("history", typeof(HistoryPage));
    Routing.RegisterRoute("goal", typeof(GoalPage));

    Dispatcher.Dispatch(async () => await InitializeShellAsync());
}

private async Task InitializeShellAsync()
{
    await Task.Delay(100);

    bool hasCompletedOnboarding = PreferencesServices.HasCompletedOnboarding();

    if (!hasCompletedOnboarding)
    {
        Console.WriteLine("[DEBUG] Navigating to onboarding...");
        await Shell.Current.GoToAsync("//onboarding");
    }
}

内容的提问来源于stack exchange，提问作者Renia