Will WP Applications for 7.5 work on WP8 also?

Question

Will applications working on wp7.5 work on wp8 also?

Answer 1

Just as an additional information from my experiments with the currently available WP8 emulators and WP8 prototype devices. Not sure if the below will be changed in the final version:

1. Some UI controls for native Silverlight apps look different on the same WP8 emulator when app is compiled for 7.5 and 8. For example, check boxes look like WP7 when app is compiled to 7.5 and look more modern if app is compiled for WP8.

2. HTML5 apps and WebBrowser control. If your app is compiled for 7.5 it will continue to run old IE9 even on WP8. If you recompile it to WP8 the WebBrowser control will use IE10 with many improvements and optimizations. Confirmed by Microsoft WP IE team.

So there are some minor differences for WP7/8 apps run on WP8.

Answer 2

Yes, WP 7, WP 7.5 apps will continue to work on WP8, including apps using XNA framework. Although WP8 apps won't work on older platforms (which is expected).

Any of the existing WP devices will NOT receive the WP8 update. They will get the WP 7.8 update, which include the new start screen and 'user experience' but nothing else.

If you write an app targeting WP7.5, it will work on all devices.

UPDATE from BUILD 2012:

• Windows Phone 8 SDK is now publicly available.
• All your existing apps targeting WP 7 or WP 7.5 will 'just work'
• You can update your apps to WP8 platform the same way you've used to upgrade WP 7 to WP 7.5, although this will make your app only work with WP8 devices. (AFAIK. can't confirm this.)

If you mark your app as a WP8 app, it will not work on WP7 or WP 7.5. Although you can mark the app as WP7.5 app, then you can use reflection to find the APIs you want, and call them (and degrade properly on a WP7.5 device where these APIs won't be available.)

In my opinion, reflection is messy, but you still have an option to support both using the same code, until WP 7.5 devices fade away. (You may have to take extra care when using reflection, because AFAIK there are some limitations to reflection on WinRT to avoid security and stability issues, which may be still true for WP8+)