Recyclerview 未显示来自 Firebase Kotlin 的数据

Question

正如标题所说，我从昨天开始使用 Kotlin。我想用来自 Firebase 的数据填充 RecyclerView。

我尝试了一些方法，我构建了一个适配器并尝试填充 RecyclerView，我的数据将进入 Firebasebase 但未显示在 RecyclerView 中，并且我没有收到任何错误。

我找不到任何关于 Kotlin 语言问题的教程

这是我的适配器：

class QuestionAdapter(var items : ArrayList<Question>): RecyclerView.Adapter<QuestionAdapter.ViewHolder>() {

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

override fun onBindViewHolder(holder: ViewHolder?, position: Int) {
    var userDto = items[position]
    holder?.titleTextView?.text = userDto.titlu
    holder?.msgTextView?.text = userDto.uid
}

override fun onCreateViewHolder(parent: ViewGroup?, viewType: Int): ViewHolder {
    val itemView = LayoutInflater.from(parent?.context)
            .inflate(R.layout.conv_layout, parent, false)

    return ViewHolder(itemView)
}

class ViewHolder(row: View) : RecyclerView.ViewHolder(row) {
    var titleTextView: TextView? = null
    var msgTextView: TextView? = null

    init {
        this.titleTextView = row?.findViewById<TextView>(R.id.titleTextView)
        this.msgTextView = row?.findViewById<TextView>(R.id.msgTextView)
    }
}
}

这是我的 Activity 代码：

 private fun populalteQuestionsList() {
    val mChatDatabaseReference = FirebaseDatabase.getInstance().reference.child(Constants.USERS).child(mUserID).child(Constants.CHAT).child(Constants.QUESTION)
    val query = mChatDatabaseReference.orderByChild("time")
    query.addListenerForSingleValueEvent(object: ValueEventListener {
        override fun onDataChange(dataSnapshot: DataSnapshot?) {
            mRecyclerView.layoutManager = LinearLayoutManager(this@MainActivity)
            mRecyclerView.setHasFixedSize(true)
            val  questions = ArrayList<Question>()
            val adapter = QuestionAdapter(questions)
            mRecyclerView.adapter = adapter
        }
        override fun onCancelled(error: DatabaseError?) {
        }
    })
}

Answer 1

Recyclerview 未显示来自 Firebase Kotlin 的数据

因为您没有在 questions ArrayList<Question>()

中添加任何数据

签入您的代码

试试这个

override fun onDataChange(dataSnapshot: DataSnapshot?) {
            mRecyclerView.layoutManager = LinearLayoutManager(this@MainActivity)
            mRecyclerView.setHasFixedSize(true)
            val  questions = ArrayList<Question>()
            val adapter = QuestionAdapter(questions)
           // add data here inside your questions ArrayList<Question>()
            mRecyclerView.adapter = adapter
        }

Answer 2

我希望在您的 adater 中定义 getItemCount() 方法，然后您可以更改以下代码...

private fun populalteQuestionsList() {
    val mChatDatabaseReference = FirebaseDatabase.getInstance().reference.child(Constants.USERS).child(mUserID).child(Constants.CHAT).child(Constants.QUESTION)
    val query = mChatDatabaseReference.orderByChild("time")
    query.addListenerForSingleValueEvent(object: ValueEventListener {
        override fun onDataChange(dataSnapshot: DataSnapshot?) {
            mRecyclerView.layoutManager = LinearLayoutManager(this@MainActivity)
            mRecyclerView.setHasFixedSize(true)
            val  questions = ArrayList<Question>()
            val question = dataSnapshot.getValue(Question::class.java)
            questions.add(question)
            val adapter = QuestionAdapter(questions)
            mRecyclerView.adapter = adapter
            adapter.notifyDataSetChanged()        
        }
        override fun onCancelled(error: DatabaseError?) {
        }
    })
}

我希望适配器有以下方法...

@Override
public int getItemCount() {
    return items.size();
}