I'm trying to make a stopwatch & countdown app for WindowPhone 7 using Silverlight for WindowPhone SDK and trying to make it run in background when it's tombstoned. In Android, I can use android.app.Service to run it in background. According to MS AppHub Quickstart, "The Windows Phone operating system doesn't allow any third-party applications to run in the background". Please help me if you have any idea for keeping the countdown running when a phone call is received or the phone goes to sleep. Thank you.
At the moment, once your app is tombstoned, your app cannot continue with any custom processes such as having your countdown continue. The Mango SDK coming out this month allows for a bit more freedom in this respect. If, however, you want to run your app under a lock screen, this is possible. You can simply do this:
PhoneApplicationService.Current.ApplicationIdleDetectionMode = IdleDetectionMode.Disabled;
Jaime Rodriguez has a great post on running under a lock screen which you can read here.
Until Mango comes out, there's no way to have your program run in the background.