从 Firebase android kotlin 获取数据时如何显示加载的项目

Posted 2023-04-19

【中文标题】从 Firebase android kotlin 获取数据时如何显示加载的项目

【英文标题】：How to display items loading while data is being fetched from Firebase android kotlin

【发布时间】：2022-01-07 08:49:37

【问题描述】：

我有一个RecyclerView 和我的Fragment。我正在从 Firebase Realtime Database 获取数据到 RecyclerView。

我需要这样做，以便在加载数据时，我看到某种加载效果。我该怎么做？

代码来自我的Fragment:

private var _binding: FragmentDayDetailBinding? = null
private val binding get() = _binding!!

private var ref: DatabaseReference? = null
private lateinit var adapter: DayDetailAdapter

override fun onCreateView(
    inflater: LayoutInflater, container: ViewGroup?,
    savedInstanceState: Bundle?
): View 
    _binding = FragmentDayDetailBinding.inflate(inflater, container, false)

    setupRecyclerView()
    initDatabase()

    return binding.root


override fun onViewCreated(view: View, savedInstanceState: Bundle?) 
    super.onViewCreated(view, savedInstanceState)

    readFromDatabase()


private fun setupRecyclerView() 
    adapter = DayDetailAdapter()
    binding.recyclerView.layoutManager = LinearLayoutManager(requireContext())
    binding.recyclerView.adapter = adapter


private fun initDatabase() 
    FirebaseApp.initializeApp(requireContext())

    ref = FirebaseDatabase.getInstance()
        .getReference("IMIT")
        .child("groups")


private fun readFromDatabase() 
    ref?.addValueEventListener(object: ValueEventListener 
        override fun onDataChange(snapshot: DataSnapshot) 
            if (snapshot.exists()) 

                val list = ArrayList<Day>()

                for (daySnapshot in snapshot.children) 
                    val day = daySnapshot.getValue(Day::class.java)

                    list.add(day!!)
                

                adapter.submitList(list)

             else 
                binding.apply 
                    lrDbEmpty.visibility = View.VISIBLE
                    recyclerView.visibility = View.INVISIBLE
                
            
        

        override fun onCancelled(error: DatabaseError) 

        
    )


override fun onDestroyView() 
    super.onDestroyView()
    _binding = null

来自RecyclerView Adapter:的代码

class ViewHolder(private val binding: ItemSubjectDetailBinding): RecyclerView.ViewHolder(binding.root) 

    fun bind(day: Day) = with(binding) 
        tvSubject.text = day.subject
        tvInfo.text = "$day.teacher, $day.type"
        tvTime.text = day.time
        tvAud.text = day.clas-s-room
    

    companion object 
        fun from(parent: ViewGroup): ViewHolder 
            val layoutInflater = LayoutInflater.from(parent.context)
            val binding = ItemSubjectDetailBinding.inflate(layoutInflater, parent, false)
            return ViewHolder(binding)
        
    


override fun onCreateViewHolder(parent: ViewGroup, viewType: Int): ViewHolder 
    return ViewHolder.from(parent)


override fun onBindViewHolder(holder: ViewHolder, position: Int) 
    with(holder) 
        bind(getItem(position))
    


class ItemComparator: DiffUtil.ItemCallback<Day>() 
    override fun areItemsTheSame(oldItem: Day, newItem: Day): Boolean 
        return oldItem == newItem
    

    override fun areContentsTheSame(oldItem: Day, newItem: Day): Boolean 
        return oldItem == newItem
    

【问题讨论】：

这段代码中到底有什么不符合您的预期？告诉我们共享代码有什么问题。你有什么错误吗？

我也认为repo 可能会有所帮助。

@AlexMamo 哇，这个 repo 对我有很大帮助，谢谢

【参考方案1】：

你已经走了一半

在片段中心创建一个progressBar

<ProgressBar
      android:id="@+id/progress_bar"
      android:layout_
      android:layout_
      />

在获取数据（onDataChange 调用）之前保持可见，然后隐藏进度条

override fun onDataChange(snapshot: DataSnapshot) 

    binding.progressBar.visibility = View.GONE

    if (snapshot.exists()) 
        // rest of your code