遍历list.count后的Swift始终为0

Question

我尝试遍历id列表以获取值。在迭代时，我想将其存储在另一个列表中。迭代后，我尝试使用新列表开始下一个方法。不幸的是，大小始终为0，但是有诅咒值。如果我在循环中将其打印出来，则其大小正确，但之后不正确。这是我的代码：

 func getUsersForFences(geofenceObject: [GeofenceObject]){
    for fence in geofenceObject{
    let ref = Database.database().reference().child("UserInFences").child(fence.fenceName!)
    ref.observeSingleEvent(of: .value, with: { (snapshot) in
        if snapshot.childrenCount > 0{
            for users in snapshot.children.allObjects as! [DataSnapshot]{
                let userItem = users.value as? [String: AnyObject]
                let userid = users.key as! String
                let timestamp = userItem?["timestamp"] as! Int
                let timestampValidation = userItem?["timestampValidation"] as! Int


                if fence.timestamp! <= timestamp && fence.timestampValidation! <= timestampValidation && timestamp <= fence.timestampValidation! {
                    let userObjecti = UserFenceObject(timestamp: timestamp, timestampValidation: timestampValidation, userId: userid)
                    self.userObjects.append(userObjecti)


                }else if fence.timestamp! >= timestamp && fence.timestampValidation! >= timestampValidation && fence.timestamp! <= timestampValidation {
                    let userObject = UserFenceObject(timestamp: timestamp, timestampValidation: timestampValidation, userId: userid)
                    self.userObjects.append(userObject)
                }
            }

        }
    });
    }

// Here its always 0
    self.getUsersInterest( userObject: userObjects)
}