问题
How to know if an activity is currently running in windows phone 7?
回答1:
As of now there is no API to get the currently running task as the assumption is that you invoked the task yourself and thus have no need to retrieve this programmaticaly. It is also important to note that unless you are working with native code or interop there is no supported way to interact with other applications other than those defined in Microsoft.Phone.Tasks
来源：https://stackoverflow.com/questions/8679250/how-to-know-the-which-activity-is-ruuning-in-windows-phone-7