更改 LiveData 后如何更新 RecyclerView 的适配器？

Question

我创建了一个片段，它在 onActivityCreated 方法中通过将查询限制为日历日期来获取 Firebase 数据。然后我将 Observers 放在我的 ViewModel 内的 LiveData 上，这会将列表传送到我的适配器。

如果我在同一个列表中添加、删除或更新项目，更改将发送到 firebase 并且适配器将它们反映在屏幕上。没问题。

但是，我正在尝试开发一个过滤器按钮，它基本上会更改 Firebase 查询的截止日期。当我 select 一个特定的过滤器时，viewModel 需要从 Firebase 检索仅限于过滤日期的数据。这会生成一个新列表，其大小与之前的列表不同。

但是，当查询发生时，Adapter 的getItemCount() 方法存储最后一个列表的大小。这个事实混淆了适配器，函数 notifyItemInserted 和 notifyItemRemoved 最终在更改过滤器后在屏幕上制作令人困惑的动画。不知道怎么回事

如何正确观察LiveData并告诉适配器？我是在 MVVM 架构上犯了错误还是忘记了一些功能？

我的片段：

class HistoryFragment : Fragment(), OnItemMenuRecyclerViewClickListener {

private lateinit var mSecurityPreferences: SecurityPreferences
private lateinit var viewModel: BalancesViewModel
private lateinit var adapter: BalancesAdapter

override fun onCreateView(
    inflater: LayoutInflater,
    container: ViewGroup?,
    savedInstanceState: Bundle?
): View? {
    setHasOptionsMenu(true)

    viewModel = ViewModelProvider(this).get(BalancesViewModel::class.java)
    adapter = BalancesAdapter(requireContext())
    mSecurityPreferences = SecurityPreferences(requireContext())

    return inflater.inflate(R.layout.fragment_history, container, false)
}

override fun onActivityCreated(savedInstanceState: Bundle?) {
    super.onActivityCreated(savedInstanceState)

    setupFilter()

    //Setup adapter
    adapter.listenerMenu = this
    recycler_view_history.adapter = adapter

    //Fetch data based in filter by date
    viewModel.fetchBalances(mSecurityPreferences.getStoredLong(FILTER_DATE))

    // Put logic to listen RealTimeUpdates
    viewModel.getRealTimeUpdates(mSecurityPreferences.getStoredLong(FILTER_DATE))

    viewModel.balances.observe(viewLifecycleOwner, Observer {
        adapter.setBalances(it)
    })

    viewModel.balance.observe(viewLifecycleOwner, Observer {
        adapter.addBalance(it)
    })

}

override fun onCreateOptionsMenu(menu: Menu, inflater: MenuInflater) {
    inflater.inflate(R.menu.history_menu_filter, menu)
    super.onCreateOptionsMenu(menu, inflater)
}

override fun onOptionsItemSelected(item: MenuItem): Boolean {
    when (item.itemId) {
        R.id.item_menu_filter_this_month -> {
            updateFilter(THIS_MONTH)
        }
        R.id.item_menu_filter_two_months -> {
            updateFilter(TWO_MONTHS)
        }
        R.id.item_menu_filter_last_six_months -> {
            updateFilter(LAST_SIX_MONTHS)
        }
        R.id.item_menu_filter_all -> {
            updateFilter(ALL_MONTHS)
        }
    }
    return super.onOptionsItemSelected(item)
}

private fun setupFilter() {
    var filterOption = mSecurityPreferences.getStoredLong(FILTER_DATE)
    if (filterOption == 0L){
        filterOption = HandleDate.getLongToFilter(LAST_SIX_MONTHS)
        mSecurityPreferences.storeLong(FILTER_DATE, filterOption)
    }
}

private fun updateFilter(filterOption: Int){
    val newFilterOption = HandleDate.getLongToFilter(filterOption)
    mSecurityPreferences.storeLong(FILTER_DATE, newFilterOption)
    updateUI()
}

private fun updateUI(){
    viewModel.fetchBalances(mSecurityPreferences.getStoredLong(FILTER_DATE))
    viewModel.getRealTimeUpdates(mSecurityPreferences.getStoredLong(FILTER_DATE))

}
}

我的视图模型：

class BalancesViewModel : ViewModel() {

private val userReference = FirebaseAuth.getInstance().currentUser!!.uid
private val dbUserReference = FirebaseDatabase.getInstance().getReference(userReference)

private val _balances = MutableLiveData<List<Balance>>()
val balances: LiveData<List<Balance>>
    get() = _balances

private val _balance = MutableLiveData<Balance>()
val balance: LiveData<Balance>
    get() = _balance

private val _result = MutableLiveData<Exception?>()
val result: LiveData<Exception?>
    get() = _result


fun addBalance(balance: Balance) {
    balance.id = dbUserReference.push().key
    dbUserReference.child(NODE_BALANCES).child(balance.id!!).setValue(balance)
        .addOnCompleteListener {
            if (it.isSuccessful) {
                _result.value = null
            } else {
                _result.value = it.exception
            }

        }
}

private val childEventListener = object : ChildEventListener {
    override fun onCancelled(error: DatabaseError) {
    }

    override fun onChildMoved(snapshot: DataSnapshot, p1: String?) {
    }

    override fun onChildChanged(snapshot: DataSnapshot, p1: String?) {
        val balance = snapshot.getValue(Balance::class.java)
        balance?.id = snapshot.key
        _balance.value = balance
    }

    override fun onChildAdded(snapshot: DataSnapshot, p1: String?) {
        val balance = snapshot.getValue(Balance::class.java)
        balance?.id = snapshot.key
        _balance.value = balance
    }

    override fun onChildRemoved(snapshot: DataSnapshot) {
        val balance = snapshot.getValue(Balance::class.java)
        balance?.id = snapshot.key
        balance?.isDeleted = true
        _balance.value = balance
    }
}

fun getRealTimeUpdates(longLimitDate: Long) {
    dbUserReference.child(NODE_BALANCES).orderByChild(COLUMN_DATE_MILLI)
        .startAt(longLimitDate.toDouble()).addChildEventListener(childEventListener)
}

fun fetchBalances(longLimitDate: Long) {
    dbUserReference.child(NODE_BALANCES).orderByChild(COLUMN_DATE_MILLI)
        .startAt(longLimitDate.toDouble())
        .addListenerForSingleValueEvent(object : ValueEventListener {
            override fun onCancelled(error: DatabaseError) {}

            override fun onDataChange(snapshot: DataSnapshot) {
                if (snapshot.exists()) {
                    val listBalances = mutableListOf<Balance>()
                    for (balanceSnapshot in (snapshot.children)) {
                        val balance = balanceSnapshot.getValue(Balance::class.java)
                        balance?.id = balanceSnapshot.key
                        balance?.let { listBalances.add(it) }
                    }
                    listBalances.sortByDescending { it.dateMilli }
                    _balances.value = listBalances
                   
                }
            }

        })
}

fun updateBalance(balance: Balance) {
    dbUserReference.child(NODE_BALANCES).child(balance.id!!).setValue(balance)
        .addOnCompleteListener {
            if (it.isSuccessful) {
                _result.value = null
            } else {
                _result.value = it.exception
            }

        }
}

fun deleteBalance(balance: Balance) {
    dbUserReference.child(NODE_BALANCES).child(balance.id!!).setValue(null)
        .addOnCompleteListener {
            if (it.isSuccessful) {
                _result.value = null
            } else {
                _result.value = it.exception
            }

        }
}

我的适配器：

class BalancesAdapter(private val context: Context) :
RecyclerView.Adapter<BalancesAdapter.BalanceViewModel>() {

private var balances = mutableListOf<Balance>()

override fun onCreateViewHolder(parent: ViewGroup, viewType: Int) =
    BalanceViewModel(
        LayoutInflater.from(parent.context)
            .inflate(R.layout.item_recyclerview_balance, parent, false)
    )
override fun getItemCount() = balances.size

override fun onBindViewHolder(holder: BalanceViewModel, position: Int) {
    holder.view.text_view_value_balance_item.text = balances[position].value
    holder.view.text_view_date_item.text = balances[position].date
}

fun setBalances(balances: List<Balance>) {
    this.balances = balances as MutableList<Balance>
    notifyDataSetChanged()
}

fun addBalance(balance: Balance) {
    val index = balances.indexOf(balance)
    if (!balances.contains(balance)) {
        balances.add(balance)
        notifyItemInserted(index)
    } else {
        if (balance.isDeleted) {
            balances.removeAt(index)
            notifyItemRemoved(index)
        } else {
            balances[index] = balance
        }
    }
    notifyItemRangeChanged(index, itemCount)
}

class BalanceViewModel(val view: View) : RecyclerView.ViewHolder(view)

}

感谢您的关注。

Answer 1

好的，我问这个问题已经 4 天了，在对这个项目感到有点沮丧之后，我回到 Whosebug 来post 我自己的答案。

我显示的代码中的问题出在我的适配器的 addBalance 方法中。

当我创建 Balance 数据模型时，我设置了 isDeleted 属性来标识它已被删除。进入 Firebase 后，它会收到 NULL 值，因此它不再存在。

然后，因为我有两个侦听器（一个在 addListenerForSingleValueEvent 方法中定义，另一个在 addChildEventListener 方法中定义），当 Firebase 数据发生变化时，一个最终会触发另一个，但我没有想详细讨论那个问题。事实上，我检查过我的 addBalance 方法在我删除一个对象后被调用，导致该对象被插入回适配器的数据列表，甚至在 Firebase 中的删除操作结束之前。

所以我改变了我的方法的逻辑，以确保我的对象被删除，并且只在检查 isDeleted 属性后将它包含在我的适配器列表中。

fun dealWithBalance(balance: Balance){

    val index = balances.indexOf(balance)
    if(balance.isDeleted && balances.contains(balance)){
        balances.removeAt(index)
        notifyItemRemoved(index)
    } else if(!balance.isDeleted && !balances.contains(balance)){
        balances.add(balance)
    } else if(index >= 0){
        balances[index] = balance
        notifyItemChanged(index)
    }
}

我将 addBalance 重命名为 dealWithBalance...

更改 LiveData 后如何更新 RecyclerView 的适配器？

How I can update my adapter for RecyclerView after change my LiveData?

observers

mvvm

android-adapter

android-livedata