Recycler View 活动回调

Question

我正在尝试为单个回收器视图项实现单击侦听器，并从我的活动中使用单击的数据运行方法（单个借用者）。

如何处理？我是 kotlin 的新手，所以一步一步的指导会很有帮助:)

谢谢！

MainActivity：

val db by lazy { Database.getInstance(applicationContext).database }

fun startDebtActivity() {
    val intent = Intent(this, AddDebtActivity::class.java)
    startActivity(intent)
}

override fun onCreate(savedInstanceState: Bundle?) {
    super.onCreate(savedInstanceState)
    setContentView(R.layout.activity_main)

    addDebtBtn.setOnClickListener {
        startDebtActivity()
    }

    thread {
        var borrowers = db.borrowers()
            .getAll()

        runOnUiThread {
            val debtsSum = borrowers.sumByDouble { it.debt }

            // update sum of debts
            summary.text = debtsSum?.toBigDecimal().setScale(2, 2).toString()
            // update item list
            recycler.apply {
                layoutManager = LinearLayoutManager(this@MainActivity)
                adapter = BorrowersListAdapter(borrowers)
            }
        }
    }
}

适配器：

class BorrowersListVh(view: View): RecyclerView.ViewHolder(view) {
    fun refreshData(borrower: Borrower) {
        itemView.borrowersListName.text = borrower.name
        itemView.borrowersLisDebt.text = borrower.debt.toString()

        itemView.setOnClickListener {
            Log.e("info", "Clicked")
        }
    }

    public interface BorrowerClickCallbacks {
        fun onItemClick(position: Int)
    }
}

class BorrowersListAdapter(private val dane: List<Borrower>) :  RecyclerView.Adapter<BorrowersListVh>() {
    override fun onCreateViewHolder(parent: ViewGroup, viewType: Int): BorrowersListVh {
        return BorrowersListVh (
            LayoutInflater.from(parent.context).inflate(R.layout.borrowers_list_item, parent,false)
        )
    }

    override fun getItemCount(): Int = dane.size

    override fun onBindViewHolder(holder: BorrowersListVh, position: Int) {
        val borrower: Borrower = dane[position]
        holder.refreshData(borrower)

        // add notify
    }
}

Answer 1

1) 这里的答案适用于 Kotlin 和 Java：

How to implement click listener callback

2) 仅限 Kotlin（Lambda）：

在您的适配器中： 添加一个名为 listener 的属性，它是您从活动或片段传递的 lambda：

class MyAdapter(private val listener: (position: Int) -> Unit) : RecyclerView.Adapter<MyAdapter.MyViewHolder>() {

    ...

    inner class MyViewHolder(itemView: View) : RecyclerView.ViewHolder(itemView), View.OnClickListener {

        init {
            itemView.setOnClickListener(this)
        }

        override fun onClick(v: View?) {
            listener.invoke(adapterPosition)
            //or listener(adapterPosition)
        }
    }

}

在你的 Activity/Fragment onCreate() 设置 recyclerview 的布局管理器后：

recyclerView.adapter = MyAdapter { position ->
    //Do anything you like when some item gets click in your adapter you 
    //can use the position
}

小心使用内部类，因为它们可能会导致您的应用出现内存泄漏，为了更安全，您可以改用嵌套类。

Answer 2

您可以通过向您的Borrower 添加一个回调函数来轻松做到这一点。

给定类型：

// UI stands for User Interface
data class BorrowerUI(val borrower: Borrower, val onClick: (Borrower) -> Unit)

然后将您的RecyclerView.Adapter 更改为接收List<BorrowerUI> 而不是List<Borrower>。

之后稍微更改一下您的 refreshData 实现：

class BorrowersListVh(view: View): RecyclerView.ViewHolder(view) {
    fun refreshData(borrowerUI: BorrowerUI) {
        itemView.borrowersListName.text = borrower.name
        itemView.borrowersLisDebt.text = borrower.debt.toString()

        itemView.setOnClickListener {
            Log.e("info", "Clicked")
            borrowerUI.onClick(borrowerUI.borrower)
        }
    }
}

最后在您的Activity 中创建RecyclerView.Adapter

class YourActivity: AppCompatActivity() {


     override fun onCreate(savedInstanceState: Bundle?) {
         super.onCreate(savedInstanceState)
         thread {
              var borrowers = 
                  db.borrowers()
                     .getAll()
                     .map { BorrowerUI(it) { onBorrowerClick(it) } }

              runOnUiThread {
                  val debtsSum = borrowers.sumByDouble { it.debt }

                  // update sum of debts
                  summary.text = debtsSum?.toBigDecimal().setScale(2, 2).toString()
                  // update item list
                 recycler.apply {
                     layoutManager = LinearLayoutManager(this@MainActivity)
                     adapter = BorrowersListAdapter(borrowers)
                 }
               }
         }
     }

     fun onBorrowerClick(borrower: Borrower) {
         // Create a toast?
     }
}

Answer 3

为您的适配器构造函数提供一个附加属性，用于响应被点击的借款人的回调：

class BorrowersListAdapter(private val dane: List<Borrower>, val onItemClicked: (Borrower) -> Unit) //...

那么在绑定views的时候，你可以在item view上设置一个监听器来调用与新关联的Borrower的回调：

override fun onBindViewHolder(holder: BorrowersListVh, position: Int) {
    val borrower: Borrower = dane[position]
    holder.refreshData(borrower)
    holder.itemView.setOnClickListener {
        onItemClicked(borrower)
    }
}

然后在你的Activity中，你可以创建一个匹配回调函数签名的函数。名字无关紧要。

fun onBorrowerClick(borrower: Borrower) {
    Log.i("borrower clicked", borrower.toString())
}

当你实例化适配器时，将此函数作为回调传递给构造函数。

adapter = BorrowersListAdapter(borrowers, ::onBorrowerClick)

---

旁注，您应该使用lifecycleScope 来启动协程，而不是像您一样直接使用线程，这样您就不会将 Activity 泄漏到后台线程：

override fun onCreate(savedInstanceState: Bundle?) {
    super.onCreate(savedInstanceState)
    setContentView(R.layout.activity_main)

    addDebtBtn.setOnClickListener {
        startDebtActivity()
    }

    lifecycleScope.launch {
        val borrowers = withContext(Dispatchers.IO) {
            db.borrowers()
                .getAll()
        }

        val debtsSum = borrowers.sumByDouble { it.debt }

        // update sum of debts
        summary.text = debtsSum?.toBigDecimal().setScale(2, 2).toString()
        // update item list
        recycler.apply {
            layoutManager = LinearLayoutManager(this@MainActivity)
            adapter = BorrowersListAdapter(borrowers, ::onBorrowerClick)
        }
    }
}