when ever i try to use firebase in my flutter app it crush and stop working.

here is the only code im using:

final CollectionReference numbersdb= Firestore.instance.collection("main");

   getnumbers() {
    print(  numbersdb.snapshots().map((event){
      return numbersfromQS(event);

  List<VisrusNumbers> numbersfromQS(QuerySnapshot snapshot){
    return snapshot.documents.map((doc){
      return VisrusNumbers(
        numberIndecator: doc.data['title'],
        number: doc.data['number']

and if counts i used http before and kept the dependence but even after i removed it didnt work