Work required to better enable adding platforms to MAUI

[PureWeen]

Description

These items are based on a quick spike adding WPF here
This is in no way an indication of future plans. This is just PureWeen testing something out and seeing areas where we could easily expose some more public APIs.

• Make an interface for AlertManager and make it public
• OpenWindowRequest only accepts IPersistedState and a specific args for WinUI which makes passing in startup args awkward.
• LifeCycle commands on pages need to be made public or interface driven (sendnavigated, sendappearing, etc...)
• ModalNavigationManager needs a public interface
• AlertManager needs a public interface
• GestureManager needs a public interface
• WinUI targets need to be shifted so they are conditional on WinUI. Currently if the OS is windows we assume WinUI which makes creating a project with <UseWPF> not possible
  • Similar issue here around forms [Windows] Can't include MAUI and WinForms in the same project #6450

First impression

You can get pretty far with the current implementation.

I was able to get some features here working https://github.com/PureWeen/maui/tree/wpf_separate_project/src/Controls/samples/Controls.Sample.WPF.

• Handlers
  • This is really the meat of it. If you just filled in all the basic control handlers (not even page level) this would cover about 90 percent of a MAUI app.
• Fixing WinUI targets is the most important thing to fix in order to be able to do UseMauiCore/UseMaui alongside UseWPF (this is only applicable to windows based TFMS)

We've moved this issue to the Backlog milestone. This means that it is not going to be worked on for the coming release. We will reassess the backlog following the current release and consider this item at that time. To learn more about our issue management process and to have better expectation regarding different types of issues you can read our Triage Process.

[rmarinho]

Did we get an idea what we need to change on the targets to make condition based on WinUI and not windows?!

[PureWeen]

Did we get an idea what we need to change on the targets to make condition based on WinUI and not windows?!

Yea I basically have those changes here
main...PureWeen:maui:wpf_separate_project

For my spike I'm keying off of UseWpf but it'd probably be better to key off of something inside WinUI instead.

Replace this conditional here
main...PureWeen:maui:wpf_separate_project#diff-9da24614831c308827a1ae533ffea392c97638c261dd42bd0f5226baa136d16eR23

With something a bit more elegant

[jsuarezruiz]

Required changes available here net10.0...fix-12947