How can i get a link to a running Activity of third-party application with reflection

I need to get a link to a running Activity of third-party application. Can anyone help me? I analyzed the android source code and i know that any activity has a PhoneWindow instance. Maybe this instance will be stored somewhere after creation... I need to get access to a view of Activity that is running at this moment. I tried to get access to the WindowManagerGlobal class to the mViews field but it seems like this field contain just views of my application because i think WindowsManager was created with my application context. Maybe there is a way to get WindowManager of other application or maybe i need to get access to PackageManagerService or other Service/Manager...Thanks for your help!