Intent - if activity is running, bring it to front, else start a new one (from notification)

Question

My app has notifications, which - obviously - without any flags, start a new activity every time so I get multiple same activities running on top of each other, which is jus

Answer 1

This is old thread, but for all those who is still seeking for answer, here is my solution. It is purely in code, without manifest settings:

private static PendingIntent prepareIntent(Context context) {
  Intent intent = new Intent(context, MainActivity.class);
  intent.setFlags(Intent.FLAG_ACTIVITY_SINGLE_TOP | Intent.FLAG_ACTIVITY_CLEAR_TOP);      
  return PendingIntent.getActivity(context, NON_ZERO_REQUEST_CODE, intent, 
    PendingIntent.FLAG_UPDATE_CURRENT);
}

Here FLAG_ACTIVITY_SINGLE_TOP opens existing activity if it is at the top of task stack. If it is not at the top, but inside stack, FLAG_ACTIVITY_CLEAR_TOP will remove all activities on top of target activity and show it. If activity is not in the task stack, new one will be created. A crucially important point to mention - second parameter of PendingIntent.getActivity(), i.e. requestCode should have non-zero value (I even called it NON_ZERO_REQUEST_CODE in my snippet), otherwise those intent flags will not work. I have no idea why it is as it is. Flag FLAG_ACTIVITY_SINGLE_TOP is interchangeable with android:launchMode="singleTop" in activity tag in manifest.