firebase - flutter / dart How can check if a document exists in firestore?

Question

I try to query using a bool if a document exists on the cloudfirestore or not. Unfortunately, my code does not work

I tried the following, but the bool does not change.

getok() {
  bool ok;
  Firestore.instance.document('collection/$name').get().then((onexist){
      onexist.exists ? ok = true : ok = false;
    }
  ); 
  if (ok = true) {
    print('exist');
  } else {
    print('Error');
  }
}

Answer 1

Waitting for answers