WP7 apps to Win8?

So Ive had an idea for an app I was going to write for the WP7. It was on the back burner till news of the Win8 came about.

 If I was going to start from scratch, should I write it for the phone and convert it later?

 Whats involved in converting it from WP7 to Win8?

Should I be applying certain models, patterns & practice for the transition?

 Any advice, useful links? 

Thanks 

If you strictly follow the MVVM pattern the majority of you code should port over with little effort. "Little effort" does not mean "no effort", though.

They're completely different user interfaces and require UIs to match the platform. Not sure that Windows Phone app would port to Windows 8 or vice versa.

I thought there was mention of being able to make your WP7 apps work on Win8 Metro. Im not so naive as to think there is a button click (wizard) to accomplish this but I thought it might be a feature/marketing tool to increase the app count for both OS to attract developers?

 Fine, Ill stick with MVVM. Thanks! 

Yeah, that was before when none of us knew what Windows 8 development would be like, and there was the speculation that WP7 apps, which are generally just Silverlight apps, would be able to just run on Windows 8.

In reality, you're web services will be the same, but Xaml/C# will be different for WP and Windows 8 metro. Yeah there are simlarities, but in reality I think you're solution would consist of, 1) Web Services projects, 2) Windows Phone project, 3) Metro App project. #2 and #3 would consume #1, but I think you're looking at two different projects.

Thanks mate, that cleared that up.

@mikexkearney:I'm just in the process of converting my 'Live tile Browser' windows phone app to WinRT:

Phone App (it's free): http://windowsphone.com/s?appid=d68906de-da5d-4f64-9b88-154f1f5d3c07

WinRT App (Screenshots): http://websurfaces.co.uk/2012/03/09/live-tile-browser-for-windows-8/

If you fire up the app on your phone then look at the WinRT screen shots of the WinRT App I am developing you will see that while the data is the same, nobody in their right mind would want to use the same  UI!. 

I  am finding there are lots more opportunities (quick wins if you like) with WinRT.

Incidentally I also have a Silverlight version of this app here which I am planning on converting to HTML5 (one day)

Needless to say all the back ends are the same although I didn't use MVVM as I don't like having that overhead on 'single developer' apps (controversial I know).

PS Shoot me  but so  far the WinRT app is "fast and fluid"!

Consider using Portable Class libraries.

"Using a Portable Class Library project, you can build portable assemblies that work without modification in .NET Framework, Metro style, Silverlight, Windows Phone 7, and Xbox 360 apps."

More Info here.

I am also currently looking into the MVPVM design pattern (note the P).

http://msdn.microsoft.com/en-us/magazine/hh580734.aspx