How to develop Windows Phone 7.5 compatibile app?

Question

I am starting first project for Windows Phone and it should work on at least Windows Phone 7.5. My question is if should I write app on Windows Phone 7.5 or should I write two app versions - once for Windows Phone 7.5 and another for Windows Phone 8?

I know that app which works on WP7.5 will also work on WP8 but what would you recommend? What would you do?

If you think that writing two apps for both versions is a better idea then should I write app on WP8 first and at the end remove special WP8 features to downgrade it for WP7.5 or maybe I should write WP7.5 app and then add some WP8 features to upgrade it to WP8?

I am asking because I want to learn WP developement and I have two tutorials: "WP7 jumpstart" and "WP8 jumpstart" tutorials (from MSDN) and I am wondering If I can skip WP7 and start directly with WP8?

Answer 1

Standard way will be to create a Windows Phone Class Library that will contain all the code except Page, View or Windows 8 specific code and than create Windows Phone App and set dependency to above created Library project. Now as Rowland Shaw as suggested you can target the Windows Phone app to 7.5 so that it will work for Windows 8 as well and if you want to use any Windows 8 specific API you can create separate application with same Library reference so that all the common code will not be duplicated.

Referr MSDN Link for the same.

Answer 2

If you wish to normally support all screen sizes, you should create 2 apps. Because WP7.x supported only 1 screen resolution, and running on WP8.x with larger screen the app will remain small size.

Answer 3

You would have to use WP7.5 if you are not going to impelement any feature which is present in only WP8