Question

There are a class of Android applications that enable password protection on certain user-specified apps; for example, Android Protector. I need to approach this problem from a different direction.

Is it possible to create an application that blocks all activity launches unless they are on a predefined whitelist? Will there be unintended consequences with this approach? I am familiar with Android basics and have written a few reasonably simple apps, but I’m still trying to figure out how these “Protector” apps intercept the launch intents correctly. Would someone mind giving me a brief overview on the correct way to do this?

The basic problem is that we have a generic Android phone that needs to be locked down so that our clients (internal only) can access our custom applications without being able to play “Need for Speed”, etc. I would like to remove the carrier bloatware, but rooting the device seems like it would be a maintenance headache. We want the setup for each phone to be as simple as installing a few custom applications.

Answer 1

Edited to elaborate on the solution

Overview

My simple solution was to add a new service and activity to my application. The service uses Handler and postDelayed to continuously schedule the monitoring task. The monitoring task checks that the current activity is on the whitelist. Getting the currently running activity involves ActivityManager and a call to getRunningTasks. After finishing the check, the monitoring task schedules itself to run again after X seconds (1, in my case).

If the activity on top is not on the whitelist, we launch the blocking activity which pops up over whatever is currently running. The key part of the blocking activity is that it overrides onBackPressed, preventing the user from simply going back to the “bad” activity. Pressing the Home key is the only way (to my knowledge) to leave this screen.

Tips

• Build a backdoor into the lock screen. For example, my solution prompts for a password on a long-press of the back key. After entering the correct password, the monitor service goes to sleep for 5 minutes so I can do my administrative work
• Display the name of the blocked activity
• Gather a good whitelist before turning this on! Activities you should definitely whitelist: the launcher, package installer, your own app (obviously), the browser, if your app has a web-based component

I don’t like that my service is constantly looping in the background; it seems wasteful. I’d like to find some way to be notified when a new task is being launched, but I couldn’t find a way to do that. The battery usage for my particular value of the monitor period and my particular phone is acceptable; though you should definitely test before adopting this yourself.