返回单元错误

Question

我正在尝试在swift中创建一个消息传递应用程序。但我在创建自定义tableview单元格时遇到错误，我不知道如何解决这个问题。我创建了2个自定义单元格，我正在检查代码中我必须使用的单元格。

代码：

    func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell {

    let uid = FIRAuth.auth()?.currentUser?.uid

    let ref = FIRDatabase.database().reference()
    let uidReference = ref.child("Users").child(uid!)

    uidReference.observeSingleEvent(of: .value, with: { (snapshot) in

        if let dictionary = snapshot.value as? [String: AnyObject] {
            let message = self.messages[indexPath.row]

            if message.Sender == dictionary["Username"] as? String {
                let cell = self.messagesTableView.dequeueReusableCell(withIdentifier: "otherMessageCell") as! OtherMessageTableViewCell

                let message = self.messages[indexPath.row]

                cell.sender.text = message.Sender
                cell.message.text = message.Message

                let uid = FIRAuth.auth()?.currentUser?.uid

                let ref = FIRDatabase.database().reference()
                let uidReference = ref.child("Users").child(uid!)

                uidReference.observeSingleEvent(of: .value, with: { (snapshot) in

                    if let dictionary = snapshot.value as? [String: AnyObject] {
                        if(message.Sender! == dictionary["Username"]! as! String) {
                            cell.sender.textAlignment = .right
                            cell.message.textAlignment = .right
                        }else{
                            cell.sender.textAlignment = .left
                            cell.message.textAlignment = .left
                        }
                    }
                }, withCancel: nil)

                let usernameReference = ref.child("Usernames").child(message.Sender!)

                usernameReference.observeSingleEvent(of: .value, with: { (snapshot) in

                    if let dictionary = snapshot.value as? [String: AnyObject] {
                        let uid = dictionary["UID"] as! String
                        let uidReference = ref.child("Users").child(uid)

                        uidReference.observeSingleEvent(of: .value, with: { (snapshot) in

                            if let dictionary = snapshot.value as? [String: AnyObject] {
                                let imageLink = dictionary["Image Link"] as! String

                                cell.profileImage.loadImageWithURLString(urlString: imageLink)
                            }
                        }, withCancel: nil)
                    }
                }, withCancel: nil)

                return cell
            }else{
                let cell = self.messagesTableView.dequeueReusableCell(withIdentifier: "selfMessageCell") as! SelfMessageTableViewCell

                let message = self.messages[indexPath.row]

                cell.sender.text = message.Sender
                cell.message.text = message.Message

                let uid = FIRAuth.auth()?.currentUser?.uid

                let ref = FIRDatabase.database().reference()
                let uidReference = ref.child("Users").child(uid!)

                uidReference.observeSingleEvent(of: .value, with: { (snapshot) in

                    if let dictionary = snapshot.value as? [String: AnyObject] {
                        if(message.Sender! == dictionary["Username"]! as! String) {
                            cell.sender.textAlignment = .right
                            cell.message.textAlignment = .right
                        }else{
                            cell.sender.textAlignment = .left
                            cell.message.textAlignment = .left
                        }
                    }
                }, withCancel: nil)

                let usernameReference = ref.child("Usernames").child(message.Sender!)

                usernameReference.observeSingleEvent(of: .value, with: { (snapshot) in

                    if let dictionary = snapshot.value as? [String: AnyObject] {
                        let uid = dictionary["UID"] as! String
                        let uidReference = ref.child("Users").child(uid)

                        uidReference.observeSingleEvent(of: .value, with: { (snapshot) in

                            if let dictionary = snapshot.value as? [String: AnyObject] {
                                let imageLink = dictionary["Image Link"] as! String

                                cell.profileImage.loadImageWithURLString(urlString: imageLink)
                            }
                        }, withCancel: nil)
                    }
                }, withCancel: nil)

                return cell
            }
        }

    }, withCancel: nil)
}

我得到的错误是：void函数中出现意外的非void返回值。

我希望有人可以帮助我，谢谢！