Shell pages cannot work with DI

[osnipezzini]

Description

Steps to Reproduce

1. Create a Shell menu, ContentPage and a ViewModel
2. Configure Shell, Page and VM in DependecyInjection in builder.Services on MauiProgram
3. Initialize App constructor with Shell, and ContentPage with ViewModel

Expected Behavior

Application starts fine

Actual Behavior

System.MissingMethodException: 'Cannot dynamically create an instance of type 'MauiProject.Pages.LoginPage'. Reason: No parameterless constructor defined.'

Basic Information

• Version with issue: 6.0.101-preview.9.1843
• IDE: 17.0.0-pre.7.0 - D:\ProgramData\VisualStudio\2022\Preview

Reproduction Link

https://github.com/osnipezzini/MauiShell

[PureWeen]

This is more a DataTemplate enhancement then being shell specific

Making this code work with IServicePRovider would mean that Shell would now create pages via DI container

maui/src/Controls/src/Core/ElementTemplate.cs

Line 67 in 1013986

object item = LoadTemplate();

And then there's a little bit of extra work to make the global routes work with IServiceProvider

[osnipezzini]

I believe you are right, but anyway this needs to be fixed as it is the central part of the project.

Or if you have an alternative I don't know.

[pictos]

Maybe you can use RouteFactoring for that. It will allow you to create your page in a more complex way. Isn't ideal but can be a workaround.

[osnipezzini]

Maybe you can use RouteFactoring for that. It will allow you to create your page in a more complex way. Isn't ideal but can be a workaround.

Could you give me an example?

[brunck]

@PureWeen I'm interested in taking a crack at this, unless you think it's something that requires work from the regular team.

[pictos]

@osnipezzini

Could you give me an example?

Yes, I did a live code session where a cover this approach, we are talking in Portuguese but you can take the code as a reference.

[PureWeen]

@brunck go for it!

I haven't dug into this too much yet so I'm not sure how tricky it'll be or won't be.

I could also be wrong with my thinking here :-)
#3147 (comment)

[brunck]

@PureWeen Thanks. Your comment makes sense, the problem I'm running into is that when the ElementTemplate constructor you mention is getting invoked, it seems to be before anything like the IApplication is getting set up with the MauiContext with the IServiceProvider that has what we need, etc. There is an IServiceProvider potentially available that we can shove in there via ProvideValue, but it's not the IServiceProvider that we need; it has things like IXamlTypeResolver in it.

[osnipezzini]

@osnipezzini

Could you give me an example?

Yes, I did a live code session where a cover this approach, we are talking in Portuguese but you can take the code as a reference.

Just now i realize, what you want to say, but this is not a workaround for me, i'm using yet DI in Xamarin Forms but injecting in Page constructor with : BindingContext = Start.GetService(), but it's a good replacement for my approach