Android: launch any activity to start in the background?

Question

If I'm writing my own Android app, I know how to structure it as a Service so it will start running in the background.

However, is there a way to launch an existing app (for example, any random .apk from the Play Store) so that it starts up in the background, without its screen taking over the display?

Alternatively, I'd be willing to launch the app, force it into the background, and redisplay the window of the previous app (whatever it might have been) that was running in the foreground. I don't know how to programmatically put the current app in the background and then determine the previous app and bring it back to the foreground.

I'm willing to do this any way possible: via Java, via one or more command-line utilities, via a Tasker plugin, via an Xposed module, or whatever.

Thank you in advance for any pointers to docs or any suggestions.

Answer 1

I discovered that the #0 entry of "dumpsys activity recents" gives the currently displayed activity ... at least on my rooted Marshmallow device. This gives me what I need.