very straight forward question. My company has developed a windows phone 7 app and have been testing it on a windows phone 7 device. Can we safely assume that the same app will be backwards compatible and work seamlessly on a windows phone 8 device such as a Nokia Lumia 920?
Thanks in advance!
Yes it will work. But it won't take advantage of all the WP8 features like a real WP8 app would. I'd suggest that you create a copy of the project and update it to WP8 for a better performence. Also replace any listboxes with LongListSelectors for example.
In most scenarios it should just work, but you should check this list of known breaking changes and you should also test your app on new devices thoroughly, just in case.
For example FMRadio class is no longer working on WP8 and there are other similar issues:
App platform compatibility for Windows Phone
来源：https://stackoverflow.com/questions/13724852/are-windows-phone-7-apps-compatible-on-windows-phone-8-devices