Hide screen in 'Recent Apps List', but allow screenshots

I have tried this method and it's working. For making the screen blank in recent list and still allowing screen you can set the flag in onPause() and clear the flag in onResume().

@Override
protected void onPause() {
  super.onPause();
  getWindow().setFlags(WindowManager.LayoutParams.FLAG_SECURE,WindowManager.LayoutParams.FLAG_SECURE);
}

@Override
protected void onResume() {
    super.onResume();
    getWindow().clearFlags(WindowManager.LayoutParams.FLAG_SECURE);     
}

I think what you need is:

android:excludeFromRecents="true"

put that in your android manifest inside your <activity>(activity you want to exclude from recents)</activity>