Kotlin中RecyclerView点击触发Toast报错问题求助

问题描述 #

使用Kotlin开发时，想要实现RecyclerView条目点击弹出Toast消息，但触发了如下报错：

None of the following functions can be called with the arguments supplied: 
public open fun makeText(p0: Context!, p1: CharSequence!, p2: Int): Toast! defined in android.widget.Toast 
public open fun makeText(p0: Context!, p1: Int, p2: Int): Toast! defined in android.widget.Toast

相关代码 #

PrintActivity.kt #

package com.questionbank

class PrintActivity : AppCompatActivity() {

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        val vBinding = ActivityPrintBinding.inflate(layoutInflater)
        setContentView(vBinding.root)
        val helper = SqliteHelper(this, "myDB.sql", 1)

        var recyclerViewAdapter = CustomAdapter()
        recyclerViewAdapter.listData = helper.select()
        vBinding.myRecyclerView.adapter = recyclerViewAdapter
        vBinding.myRecyclerView.layoutManager = LinearLayoutManager(this)
        vBinding.myRecyclerView.addItemDecoration(
            DividerItemDecoration(this, DividerItemDecoration.VERTICAL)

        )

    }

    class CustomAdapter : RecyclerView.Adapter<CustomAdapter.Holder>() {
        var listData = ArrayList<questionType>()

        inner class Holder(val vBinding: QuestionLayoutRecyclerBinding) :
            RecyclerView.ViewHolder(vBinding.root) {
            fun setData(id:Int?, question: String, answer: String, exp: String) {
                vBinding.printId.text=id.toString()

                
                vBinding.myLinear.setOnClickListener {
                    // error occur
                    Toast.makeText(this@PrintActivity, "test", Toast.LENGTH_SHORT).show()
                }

            }
        }

        override fun onCreateViewHolder(parent: ViewGroup, viewType: Int): Holder {
            val vBinding = QuestionLayoutRecyclerBinding.inflate(
                LayoutInflater.from(parent.context),
                parent,
                false
            )
            return Holder(vBinding)
        }

        override fun onBindViewHolder(holder: Holder, position: Int) {
            val question = listData[position]
            holder.setData(question.id, question.question, question.answer, question.exp)
        }

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

    }

}

activity_print.xml #

<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".PrintActivity">

    <androidx.recyclerview.widget.RecyclerView
        android:id="@+id/myRecyclerView"
        android:layout_width="0dp"
        android:layout_height="0dp"
        android:layout_marginStart="32dp"
        android:layout_marginTop="32dp"
        android:layout_marginEnd="32dp"
        android:layout_marginBottom="32dp"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent"
        />
</androidx.constraintlayout.widget.ConstraintLayout>

question_layout_recycler.xml #

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:id="@+id/myLinear"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:orientation="vertical"
    android:padding="10dp">

    <TextView
        android:id="@+id/printId"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text="TextView" />

</LinearLayout>

解决方案 #

报错原因是Toast.makeText的Context参数引用错误——你在Holder的点击事件中使用this@PrintActivity，但Holder是CustomAdapter的内部类，CustomAdapter又嵌套在PrintActivity中，这种多层嵌套的this引用无法正确指向有效的Context。

提供两种可行的解决方法：

方法一：从View获取Context（推荐） #

直接借助ViewHolder中绑定的View获取Context，代码简洁且无需额外传递参数：

vBinding.myLinear.setOnClickListener {
    Toast.makeText(vBinding.root.context, "test", Toast.LENGTH_SHORT).show()
}

每个View对象都持有自身关联的Context，用vBinding.root.context或者itemView.context都能正确获取到所需的Context。

方法二：给Adapter传递Context #

在创建Adapter时传入Activity的Context，后续在Holder中使用该Context：

1. 修改CustomAdapter的构造函数，添加Context参数：

class CustomAdapter(private val context: Context) : RecyclerView.Adapter<CustomAdapter.Holder>() {
    var listData = ArrayList<questionType>()

    inner class Holder(val vBinding: QuestionLayoutRecyclerBinding) :
        RecyclerView.ViewHolder(vBinding.root) {
        fun setData(id:Int?, question: String, answer: String, exp: String) {
            vBinding.printId.text=id.toString()
            
            vBinding.myLinear.setOnClickListener {
                Toast.makeText(context, "test", Toast.LENGTH_SHORT).show()
            }
        }
    }

    // 其余 onCreateViewHolder、onBindViewHolder、getItemCount 代码保持不变
}

2. 在PrintActivity中创建Adapter时传入当前Context：

var recyclerViewAdapter = CustomAdapter(this)

内容的提问来源于stack exchange，提问作者조영민