Firebase Storage URL is FutureString

Question

in my flutter app, the user picture is loaded by Cached Network image command, which gets its url by stream builder from firestore.

I am trying to add the functionality to the user of changing his pic by pressing on the pic as following:

1. Selecting his pic with image picker.
2. upload it to firebase storage.
3. updating firestore usercollection document with new image url.

I created the below code. The problem is getDownloadURL() is not returning actual string, but "Instance of 'Future'".

so the new link stored in firestore is not correct to be used by Cached Network Image.

how can I get the actual URl String?

My Future Function Code:

Future ChangeProfilePic() async {
  String newimageurl = "";
  FirebaseStorage storage = FirebaseStorage.instance;
  Reference ref =
      storage.ref().child("ProfileImages/$globaluserid".toString());
  CollectionReference userscollectionref =
      FirebaseFirestore.instance.collection('UsersCollection');
  final ImagePicker _picker = ImagePicker();
  final XFile? image = await _picker.pickImage(source: ImageSource.gallery);
  File imagefile = File(image!.path);
  UploadTask uploadTask = ref.putFile(imagefile);
  uploadTask.whenComplete(() {
    newimageurl = ref.getDownloadURL().toString();
    print("Image Uploaded");
    userscollectionref
        .doc(globaluserid)
        .update({'User_image_link': newimageurl});
    print("Link is Updated");
  }).catchError((onError) {
    print("Error");
    print(onError);
  });
}