lateinit 属性绑定尚未初始化

Question

我知道有类似的问题，但我找不到类似的东西，我一直在研究新的东西来学习，在将 kotlin 合成器转换为 viewvbinding 模式时，我'我遇到了这个错误

kotlin.UninitializedPropertyAccessException: lateinit property binding has not been initialized
        at com.codepalace.chatbot.ui.MessagingAdapter.onBindViewHolder(MessagingAdapter.kt:60)
        at com.codepalace.chatbot.ui.MessagingAdapter.onBindViewHolder(MessagingAdapter.kt:17)

它说我必须初始化绑定，但我不知道把它放在哪里。

这是代码。

class MessagingAdapter: RecyclerView.Adapter<MessagingAdapter.MessageViewHolder>() {

var messagesList = mutableListOf<Message>()
private lateinit var binding: MessageItemBinding


inner class MessageViewHolder(itemView: View) : RecyclerView.ViewHolder(itemView) {
    init {
        itemView.setOnClickListener {

            //Remove message on the item clicked
            messagesList.removeAt(adapterPosition)
            notifyItemRemoved(adapterPosition)
        }
    }
}

override fun onCreateViewHolder(parent: ViewGroup, viewType: Int): MessageViewHolder {

    return MessageViewHolder(
        LayoutInflater.from(parent.context).inflate(R.layout.message_item, parent, false)
    )
}

override fun getItemCount(): Int {
    return messagesList.size
}

@SuppressLint("SetTextI18n")
override fun onBindViewHolder(holder: MessageViewHolder, position: Int) {
    val currentMessage = messagesList[position]


    when (currentMessage.id) {
        SEND_ID -> {
            holder.itemView.findViewById<View>(R.id.tv_message).apply {
                binding.tvMessage.text = currentMessage.message
                visibility = View.VISIBLE
            }
            holder.itemView.findViewById<View>(R.id.tv_bot_message).visibility = View.GONE
        }
        RECEIVE_ID -> {
            holder.itemView.findViewById<View>(R.id.tv_bot_message).apply {
                binding.tvBotMessage.text = currentMessage.message
                visibility = View.VISIBLE
            }
            holder.itemView.findViewById<View>(R.id.tv_message).visibility = View.GONE
        }
    }
}

fun insertMessage(message: Message) {
    this.messagesList.add(message)
    notifyItemInserted(messagesList.size)
}

Answer 1

private lateinit var binding: MessageItemBinding

你没有初始化binding对象，因为你定义它为lateinit，那么你应该定义它。

这通常在 onCreateViewHolder

override fun onCreateViewHolder(parent: ViewGroup, viewType: Int): TrackedActivityHolder {
    val inflater = LayoutInflater.from(parent.context)
    binding = DataBindingUtil.inflate<MessageItemBinding>(inflater, R.layout.message_item, parent, false)
    return MessageViewHolder(
        binding
    )
}

更新

您需要在 MessageViewHolder 构造函数中接受 MessageItemBinding 类型而不是 View，并使用 itemView.root 获取列表项的根视图。

inner class MessageViewHolder(itemView: MessageItemBinding) : RecyclerView.ViewHolder(itemView.root) {
    init {
        itemView.root.setOnClickListener {

            //Remove message on the item clicked
            messagesList.removeAt(adapterPosition)
            notifyItemRemoved(adapterPosition)
        }
    }
}

Answer 2

您收到此错误的原因是 MessageItemBinding 不应该在 Adapter 中，而应该在 ViewHolder class 中。你可以像这样制作 RecyclerView：

object MessageDiffCallback : DiffUtil.ItemCallback<Message>()
{
    override fun areItemsTheSame(
        oldItem: Message,
        newItem: Message
    ): Boolean =
            oldItem.id == newItem.id

    override fun areContentsTheSame(
        oldItem: Message,
        newItem: Message
    ): Boolean =
            oldItem == newItem
}

我假设Message是一个数据class。您必须创建此 MessageDiffCallback 并以与我类似的方式覆盖这两个方法。

现在创建 ViewHolder class:

class MessageViewHolder private constructor(
    private val binding: MessageItemBinding
) : RecyclerView.ViewHolder(binding.root)
{
    companion object
    {
        fun create(parent: ViewGroup): MessageViewHolder 
        {
            val layoutInflater = LayoutInflater.from(parent.context)
            val binding = MessageItemBinding.inflate(layoutInflater, parent, false)
            return MessageViewHolder(
                binding
            )
        }
    }

    fun bind(
        message: Messaage
    )
    {
        // Here You can do everything. 
        // You pass the message and based on this You can set up a view and use binding
    }
}

现在适配器 class

class MessageAdapter : ListAdapter<Message, MessageViewHolder>(MessageDiffCallback)
{
    override fun onCreateViewHolder(parent: ViewGroup, viewType: Int): MessageViewHolder =
            MessageViewHolder.create(parent)


    override fun onBindViewHolder(holder: MessageViewHolder, position: Int) =
            holder.bind(
                message = getItem(position),
            )
}

现在你应该有一个工作适配器。要将数据放入其中，请在 Fragment/Activity

中使用 messageAdapter.submitList(messages)

可能不是最佳答案，因为它更改了您的代码并使用了一些不同的逻辑，但它应该可以更好地工作。你可以检查google sample code here or take codelab here。注册后免费

lateinit 属性绑定尚未初始化

lateinit property binding has not been initialized

data-binding

android

kotlin

android-recyclerview

lateinit 属性 绑定尚未初始化

lateinit property binding has not been initialized

data-binding

android

kotlin

android-recyclerview

lateinit 属性绑定尚未初始化