swift - 未捕获的异常“NSInvalidArgumentException”，原因:“试图滚动到无效的索引路径

由于意外异常而终止应用程序
'NSInvalidArgumentException'，reason:'尝试滚动到无效
索引路径：{length=2，path=0-9}'
我收到这个错误我猜我需要做一个守卫或者如果让语句来避免崩溃，但是在哪里做这样的语句最好呢？

func observeMessages() {
        guard let uid = Auth.auth().currentUser?.uid, let toId = user?.id else {
            return
        }

        let userMessagesRef = Database.database().reference().child("user-messages").child(uid).child(toId)
        userMessagesRef.observe(.childAdded, with: { (snapshot) in

            let messageId = snapshot.key
            let messagesRef = Database.database().reference().child("messages").child(messageId)
            messagesRef.observeSingleEvent(of: .value, with: { (snapshot) in

                guard let dictionary = snapshot.value as? [String: AnyObject] else {
                    return
                }

                self.messages.append(Message(dictionary: dictionary))
                DispatchQueue.main.async(execute: {
                    self.collectionView?.reloadData()
                    //scroll to the last index

                    let indexPath = IndexPath(item: self.messages.count - 1, section: 0)

                    self.collectionView?.scrollToItem(at: indexPath, at: .bottom, animated: true)

                })

            }, withCancel: nil)

        }, withCancel: nil)
    }

最佳答案

请更新你的代码如下。。。
您正在后台更新self.message。收主线

func observeMessages() {
    guard let uid = Auth.auth().currentUser?.uid, let toId = user?.id else {
        return
    }

    let userMessagesRef = Database.database().reference().child("user-messages").child(uid).child(toId)
    userMessagesRef.observe(.childAdded, with: { (snapshot) in

        let messageId = snapshot.key
        let messagesRef = Database.database().reference().child("messages").child(messageId)
        messagesRef.observeSingleEvent(of: .value, with: { (snapshot) in

            guard let dictionary = snapshot.value as? [String: AnyObject] else {
                return
            }


            DispatchQueue.main.async(execute: {
                self.messages.append(Message(dictionary: dictionary))
                self.collectionView?.reloadData()
                //scroll to the last index

                let indexPath = IndexPath(item: self.messages.count - 1, section: 0)

                self.collectionView?.scrollToItem(at: indexPath, at: .bottom, animated: true)

            })

        }, withCancel: nil)

    }, withCancel: nil)
}

关于swift - 未捕获的异常“NSInvalidArgumentException”，原因:“试图滚动到无效的索引路径，我们在Stack Overflow上找到一个类似的问题：https://stackoverflow.com/questions/50948226/