.Net MAUI - AppShell navigation & dependency injection

Question

I'm playing around with .Net Maui, AppShell and dependency injection.

I try to call a page with a constructor which takes the ViewModel of this page as parameter.

The constructor looks like this:

public AuthenticationPage(AuthenticationViewModel viewModel)
{
    InitializeComponent();
    BindingContext = viewModel;
}

In my MauiProgram.cs I registered both, the page and the VM

builder.Services.AddSingleton<AuthenticationViewModel>();
builder.Services.AddSingleton<AuthenticationPage>();

My App.xaml.cs looks like this:

public partial class App : Application
{
    public App()
    {
        InitializeComponent();
        MainPage = new AppShell();
    }
}

And my AppShell.xaml looks like this:

<Shell  xmlns="http://schemas.microsoft.com/dotnet/2021/maui" 
           xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
           xmlns:pages="clr-namespace:DeepBlue.Pages"
           xmlns:auth="clr-namespace:DeepBlue.Pages.Authentication"
           x:Class="DeepBlue.AppShell">

    <!-- Login and Registration Page -->
    <ShellContent Route="login"
                  ContentTemplate="{DataTemplate auth:AuthenticationPage}">
    </ShellContent>

    <!-- Main Page -->
    <FlyoutItem Route="main"
                FlyoutDisplayOptions="AsMultipleItems">
        <ShellContent Route="dashboard"
                      ContentTemplate="{DataTemplate pages:DashboardPage}"
                      Title="Home" />
    </FlyoutItem>

</Shell>

Now when I execute my Project, I get the following error:

System.MissingMethodException: 'No parameterless constructor defined for type 'DeepBlue.Pages.Authentication.AuthenticationPage'.'

Could someone please tell me why the dependency injection does not work in this case?

If I don't implement the AppShell, everthing is working fine.... I can call AuthenticationPage as MainPage via injection from my App.xaml.cs like this:

public App(AuthenticationPage page)
{
    InitializeComponent();
    MainPage = page
}

Thanks, Phil

Answer 1

The Maui DevBlogs of January 2022 suggested that this was implemented, but it seems like it is partly removed temporary because of some issues. For now there is a workaround: Add the view which needs DI in the services in MauiProgram.cs:

// Workaround for Shell/DataTemplates:
builder.Services.AddTransient<MainPage>();
builder.Services.AddTransient<AuthenticationPage>();

Hopefully DI support for Shell and DataTemplates will be implemented soon correctly.