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I'm trying to develop an android app for the SDK version 30 that (when a button is clicked) starts listening to what apps are opened on the phone. If it detects the user opening Whatsapp, it is supposed to show a LockScreen activity over Whatsapp that makes you answer a math question before being able to use Whatsapp.

I know this can be done as their are apps like QualityTime or Forest that have similar features to restrict you from using certain apps, but I am a newbie when it comes to programming (probably obvious from my code) and feel totally stuck.

I have already figured out how to detect what app the user opened in the last second with code from stack overflow:

public String getCurrentApp() {
    String topPackageName = "None";
    if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.LOLLIPOP) {
        UsageStatsManager mUsageStatsManager = (UsageStatsManager) getSystemService("usagestats");
        long time = System.currentTimeMillis();
        List<UsageStats> stats = mUsageStatsManager.queryUsageStats(UsageStatsManager.INTERVAL_DAILY, time - 1000 * 1, time);
        // Sort the stats by the last time used
        if (stats != null) {
            SortedMap<Long, UsageStats> mySortedMap = new TreeMap<Long, UsageStats>();
            for (UsageStats usageStats : stats) {
                mySortedMap.put(usageStats.getLastTimeUsed(), usageStats);
            }
            if (!mySortedMap.isEmpty())
            {
                topPackageName = mySortedMap.get(mySortedMap.lastKey()).getPackageName();
            }
        }
    }
    return topPackageName;
}

I have another function that is started when the user clicks the button in my app to "activate" the listening process. This function keeps checking if the user opens Whatsapp and is then supposed to display the Lockscreen activity on top:

public void startListening(View view)
{
    System.out.println("Lock activated.");
    while (activated) {
        String currentlyRunningApp;
        currentlyRunningApp = getCurrentApp();
        if (currentlyRunningApp.equals("com.whatsapp"))
        {
            System.out.println("Whatsapp detected. Showing Lockscreen...");
            Intent i = new Intent(this,LockScreen.class);
            startActivity(i);
        }

        try {
            Thread.sleep(800);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
    }
}

(All of the code I have shown is in my MainActivity btw.)

I have the following permissions granted to my app:

  1. android.permission.PACKAGE_USAGE_STATS (for the getCurrentApp() function)
  2. android.permission.SYSTEM_ALERT_WINDOW (as suggested here)
  3. android.permission.ACTION_MANAGE_OVERLAY_PERMISSION (although I am not sure I even need this one)

My problem is, that instead of showing the Lockscreen activity I created, it only shows a blackscreen for the user. The Lockscreen activity itself works fine if I let the user open it through a button on the mainActivity, so the issue seems to really be that I can not properly show an activity if my app is running in the background and I want to display it on top of Whatsapp.

I have tried to look through similar questions, but all of the posts on here with similar use cases seem to be very old and outdated (i.e. this or this), as the newer versions seem to have way tighter security restrictions.

I also tried to do it with a screen overlay instead of an activity (using this source), but this doesn't even give me a blackscreen - just does nothing...

I am also aware that there are probably better ways to program the whole "listening and checking for whatsapp" part - i.e. with a service instead of a while-loop or something, but I only found out about services while researching this problem and I'd like to fix the blackscreen issue first.

tabea0806
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1 Answers1

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After lots of trial and error I figured out that the issues was indeed caused by a missing permission, but one that I could not find on any stack overflow answer related to black screen problems. On top of that, I believe it's an issue that only occurred because I used a Xiaomi device for testing.

There are currently two separate permissions for displaying screens over other apps that you will need to grant:

  1. Display over other apps, also called Display pop-up window. This is the android.permission.ACTION_MANAGE_OVERLAY_PERMISSION that I wasn't sure was even needed. So to emphasize, I definetly do need this permission.
  2. Display pop-up windows while running in the background. This is the permission I was missing.

After I allowed them both (which you can do under Settings > Apps > Manage Apps > Your App > Other Permissions) everything worked fine.

To direct the user directly to the settings menu where they can allow these permissions, I used the code from this stack overflow answer. This is also where I got the info that it's a xiaomi-specific "issue".

tabea0806
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