Question

当我使用虚拟数据时，我的RecyclerView正在工作，但在连接到Firebase数据库时显示RecyclerView的空结果。请帮助解决这个问题。

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

        var adapter = qponAdapter(generateData())
        val layoutManager = LinearLayoutManager(context)
        qponRecyclerView?.layoutManager = layoutManager
        qponRecyclerView?.itemAnimator = DefaultItemAnimator()

        qponRecyclerView?.adapter = adapter
        adapter.notifyDataSetChanged()
}

private fun generateData(): ArrayList<Company> {

    var companyReg = Company(name = "qqqqq", br = "", country = "", city = "", address = "", tel = "", value = "", qponQuantity = 0, email = "", advApproved = "false", advPassword = "", startDate = "", endDate = "", conditions = "", postApproved = "false", order = 10000, authPhone = "",nodeID = "")
    companyList.add(companyReg)
    companyList.add(companyReg)
    companyList.add(companyReg)
    companyList.add(companyReg)
    companyList.add(companyReg)
}

运行良好，在Recyclerview中显示5条记录。

private fun generateData(): ArrayList<Company> {
            val postListener = object : ValueEventListener {
                override fun onDataChange(dataSnapshot: DataSnapshot) {
                    // Get Post object and use the values to update the UI
                    //val post = dataSnapshot.getValue<Post>(Post::class.java!!)
                    // ...
                    val td = dataSnapshot.value as HashMap<*, *>



                    for (key in td.keys){
                        val post = td[key] as HashMap<*, *>

                        val companyReg = Company(name = "", br = "", country = "", city = "", address = "", tel = "", value = "", qponQuantity = 0, email = "", advApproved = "false", advPassword = "", startDate = "", endDate = "", conditions = "", postApproved = "false", order = 10000, authPhone = "",nodeID = "")

                        companyReg.name = post["Name"].toString()
                        companyReg.address = post["Address"].toString()
                        companyReg.country = post["Country"].toString()
                        companyReg.city = post["City"].toString()
                        companyReg.tel = post["Tel"].toString()
                        companyReg.value = post["qponValue"].toString()
                        //companyReg.qponQuantity = qponQuantity
                        companyReg.email = post["Email"].toString()
                        companyReg.advPassword = post["advPassword"].toString()

                        companyReg.startDate = post["startDate"].toString()
                        companyReg.endDate = post["endDate"].toString()
                        companyReg.conditions = post["Conditions"].toString()

                        companyReg.postApproved = post["PostApproved"].toString()
                        companyReg.advApproved = post["advApproved"].toString()
                        //companyReg.order = post["Order"] as! Int
                        companyReg.authPhone = post["authPhone"].toString()
                        companyReg.nodeID = key.toString()

                        println(companyReg.nodeID)
                        println(companyReg.address)


                        companyList.add(companyReg)
                    }


                }

                override fun onCancelled(databaseError: DatabaseError) {
                    // Getting Post failed, log a message
                    Log.w(TAG, "loadPost:onCancelled", databaseError.toException())
                    // ...
                }
            }
            myRef.addValueEventListener(postListener)


        return companyList
    }

它连接到Firebase数据库，但RecyclerView显示0记录。我确信它连接到数据库，因为它打印出控制台中的每个记录。

Answer 1

您现在无法返回尚未加载的内容。换句话说，您不能简单地在companyList函数之外使用onDataChange()列表，因为由于此函数的异步行为，它始终为empty。这意味着当您尝试在该函数之外使用该列表时，数据尚未从数据库中完成加载，这就是无法访问的原因。

快速解决此问题的方法是仅在onDataChange()函数中使用该列表，否则我建议您从 post 中查看我的anwser的最后一部分我在其中解释了如何使用自定义回调来完成它。您还可以查看此 video 以获得更好的理解。它适用于Android，但同样的原则适用。

Answer 2

将数据添加到列表时，需要让适配器知道其数据集发生了变化。只有这样才能重新绘制视图。

这意味着在onDataChange结束时，您应该致电notifyDataSetChanged。类似的东西：

override fun onDataChange(dataSnapshot: DataSnapshot) {
    val td = dataSnapshot.value as HashMap<*, *>

    for (key in td.keys){
        val post = td[key] as HashMap<*, *>

        ...

        println(companyReg.nodeID)
        println(companyReg.address)


        companyList.add(companyReg)
    }

    adapter.notifyDataSetChanged()
}

这很可能意味着您必须使适配器成为类的成员字段，以便可以在onDataChange()中访问它。

Android Kotlin Firebase实时数据库：RecyclerView显示空结果

2 个答案: