Prism + DryIoc crashes when trying to perform constructor injection?

Question

I'm having trouble using DryIoc for constructor injection into a ViewModel using Prism with Xamarin. I am using the Nuget package Prism.DryIoc.Forms.

In my project I get the following error in AuthenticatePage.xaml.g.cs

Unable to resolve Object {RequiredServiceType=Project.ViewModels.AuthenticatePageViewModel} with 1 arg(s) 
in wrapper Func<Xamarin.Forms.Page, Object> {RequiredServiceType=Project.ViewModels.AuthenticatePageViewModel} with 1 arg(s) 
from container
with normal and dynamic registrations:
MainPage, {ID=44, ImplType=Project.Views.MainPage}}
NavigationPage, {ID=43, ImplType=Xamarin.Forms.NavigationPage}}
AuthenticatePage, {ID=45, ImplType=Project.Views.AuthenticatePage}}

Specifically, it points to the line

private void InitializeComponent() {
        global::Xamarin.Forms.Xaml.Extensions.LoadFromXaml(this, typeof(AuthenticatePage));
    }

Of note is that if I call the following in App.OnInitialized, the object resolves fine:

c.Register<INegotiator, Negotiator>(Reuse.Singleton);
var n = c.Resolve<INegotiator>();
n.ResumeSessionAsync(); // This works fine, no problems.
await NavigationService.NavigateAsync("NavigationPage/AuthenticatePage"); // Error thrown here

If I remove the constructor injection from my ViewModel it works fine (Aside from keeping the default navigationService injection, which works fine). Even trying to inject a basic class like ILogger (no dependencies) fails.

public AuthenticatePageViewModel(INavigationService navigationService, ILogger logger) : base (navigationService)
{
    Title = "Authentication Page...";
}

I'm going to keep investigating, but is it obvious to someone here if I'm fundamentally doing something wrong? If I had to guess I would say it's to do with a conflict with Prisms built in Ioc container and DryIoc?

Edit:

I'm using the latest version of Prism.DryIoc.Forms available on NuGet (7.0.0.396) which says it includes DryIoc 2.12.26. I have so far simply followed the template available for Visual Studio which lists setting up navigation as follows:

protected override async void OnInitialized()
{
    InitializeComponent();

    var c = new Container();
    c.Register<ILogger, LoggerConsole>(Reuse.Singleton);

    c.RegisterMany(new[] { Assembly.Load("Project.UWP") },
                   serviceTypeCondition: type => type == typeof (ILocalFileHandler));

    c.Register<INegotiator, Negotiator>(Reuse.Singleton);
    // var n = c.Resolve<INegotiator>(); 
    // n.ResumeSessionAsync(); // <- This will run fine. Negotiator class has ILogger and ILocalFileHandler injected into it.

    await NavigationService.NavigateAsync("NavigationPage/AuthenticatePage");

}

protected override void RegisterTypes(IContainerRegistry containerRegistry)
{
    containerRegistry.RegisterForNavigation<NavigationPage>();
    containerRegistry.RegisterForNavigation<MainPage>();
    containerRegistry.RegisterForNavigation<AuthenticatePage>();
}

I can't find any info online on if/how I should be using Prism.DryIoc.DryIocContainerExtensions to set up navigation? Even modifying the sample app to include basic construction injection results in the error "Value Cannot Be Null" in the same xaml.g.cs file?

Answer 1

Following @Dan S.'s diagnoses suggestion as well as reading this article (http://brianlagunas.com/whats-new-in-prism-for-xamarin-forms-7-0/) I realized that I should have been using the Prism.Ioc.ContainerRegistry abstraction layer to interface with DryIoc. Prior to this I had been working directly with DryIoc's classes.

Once I modified my registration code to use Prism.Ioc.IContainerRegistry it worked perfectly.

protected override void RegisterTypes(IContainerRegistry cr)
{
    cr.Register<ILogger, LoggerConsole>();

    cr.GetContainer().RegisterMany(new[] { Assembly.Load("Project.UWP") },
                   serviceTypeCondition: type => type == typeof(ILocalFileHandler));

    cr.Register<INegotiator, Negotiator>();


    cr.RegisterForNavigation<NavigationPage>();
    cr.RegisterForNavigation<MainPage>();
    cr.RegisterForNavigation<AuthenticatePage>();
}

Answer 2

Prism 7.0 and below allows the exception to bubble up, in order to diagnose the root cause of your issue you want to better diagnose this issue I suggest you do a little try/catch to see what and where the error really is.

protected override void OnInitialized()
{
    try
    {
        // Check if there is an initialization exception
        var page = new AuthenticationPage();

        // Validate that the page resolves ok
        var page2 = Container.Resolve<object>("AuthenticationPage");

        // Validate that your ILogger interface is registered and resolves ok
        var logger = Container.Resolve<ILogger>();

        // Check for Registration/initialization exceptions
        var vm = Container.Resolve<AuthenticationPageViewModel>();
    }
    catch(Exception ex)
    {
        System.Diagnostics.Debug.WriteLine(ex);
        System.Diagnostics.Debugger.Break();
    }
}

You haven't specified at what point you're getting this error, though typically with XAML Compilation enabled you would see exceptions in the {pageName}.xaml.g.cs during compilation and not runtime. Either way, given that your exception is coming from the generated XAML code behind class, this tells me it is most likely a problem with your XAML. A very simple way to validate this is to remove all of the XAML content in your AuthenticationPage so that you have an empty page.

Given the code you've provided as part of your question, I would say you have no registration for your ILogger interface which would likely throw an exception causing the problem you're seeing. Regardless of what/where the error is, the try/catch shown above would be the easiest way to determine the root cause.