如何从RecyclerView适配器调用ViewModel.delete

Question

我想从Recyclerview Adapter调用ViewModel.delete(房间数据库(方法，但它不起作用。有什么想法吗？

我想在OnBindViewHolder中调用ViewModel，如下所示：holder.binding.ivItemWalletDelete.setOnClickListener{WalletViewModel。。。}

但我得到了错误：在一个空对象上

RecyclerView适配器(WalletListAdapter.kt(

class WalletListAdapter:
ListAdapter<Wallet, WalletListAdapter.ViewHolder>(WalletDiffCallback()){
override fun onCreateViewHolder(
parent: ViewGroup,
viewType: Int
): ViewHolder {
return ViewHolder.from(parent)
}

override fun onBindViewHolder(holder: ViewHolder, position: Int) {
val item = getItem(position)
holder.bind(item)
}
class ViewHolder private constructor(val binding: ItemWalletsBinding) :
RecyclerView.ViewHolder(binding.root) {
fun bind(item: Wallet) {
binding.wallet = item
binding.executePendingBindings()
}
companion object {
fun from(parent: ViewGroup): ViewHolder {
val layoutInflater = LayoutInflater.from(parent.context)
val binding = ItemWalletsBinding.inflate(layoutInflater, parent, false)
return ViewHolder(binding)
}
}
}
}
class WalletDiffCallback : DiffUtil.ItemCallback<Wallet>() {
override fun areItemsTheSame(oldItem: Wallet, newItem: Wallet): Boolean {
return oldItem.walletId == newItem.walletId
}
override fun areContentsTheSame(oldItem: Wallet, newItem: Wallet): Boolean {
return oldItem == newItem
}
}

ViewModel(WalletViewModel.kt(

class WalletViewModel(application: Application): AndroidViewModel(application) {
private val repository = WalletRepository(application)
private val liveWalletList = repository.getLiveDataWallets()
fun insert(wallet: Wallet){
viewModelScope.launch {
repository.insert(wallet)
}
}
fun update(wallet: Wallet){
viewModelScope.launch {
repository.update(wallet)
}
}
fun delete(wallet: Wallet){
viewModelScope.launch {
repository.delete(wallet)
}
}
fun getWalletById(walletId: Long): Wallet? {
var wallet: Wallet? = null
viewModelScope.launch {
wallet = repository.getWalletById(walletId)
}
return wallet
}
fun getAllWallets(): List<Wallet>? {
var wallets: List<Wallet>? = null
viewModelScope.launch {
wallets = repository.getAllWallets()
}
return wallets
}
fun getLiveWalletList(): LiveData<List<Wallet>> = liveWalletList
} 

Answer 1

解决这类问题的一种常见方法是创建一个将传递到适配器的回调。

在WalletListAdapter类中，传入一个接受Wallet对象的回调。

class WalletListAdapter(private val onDeleteCallback: (Wallet) -> Unit) {}

在ViewHolder中，您可以在每个回收器视图项上设置一个OnClickListener，并将Wallet对象传递给回调函数。看起来像这样：

binding.root.setOnClickListener { onDeleteCallback(item) }

最后，初始化WalletListAdapter的视图(活动、片段等(将传入一个接受Wallet对象的函数。然后在这里调用WalletViewModel的delete函数。

class WalletListActivity: Activity() {
@Inject
lateinit var viewModel: WalletViewModel
override fun onCreate(bundle: Bundle?) {
super.onCreate(savedInstanceState)

// initialize the WalletListAdapter and pass in the callback
val adapter = WalletListAdapter(::deleteWallet)
}
private fun deleteWallet(wallet: Wallet) {
viewModel.delete(wallet)
}
}

注意：您可以先用一个空构造函数初始化WalletListAdapter类，然后创建一个方法将回调函数从视图传递给WalletListAdapter类。重点是"；传播"；单击事件从适配器返回到视图，因此视图可以调用viewmodel的方法。