如何为 Fragment 声明的变量赋值，来自 onBindViewHolder 的值？

Question

我想从位置的值中为 Fragment 声明的变量赋值：从 onBindViewHolder 设置的 Int 变量。我的策略是获取 position: Int 的值来传递从 RecyclerView 列表中单击的项目的值分配，而 ListHolder 的 onClick 函数将值用于进一步的任务。

我的源代码导致异常：

androidx.fragment.app.Fragment$InstantiationException: Unable to instantiate fragment info.shutterpress.idols.DetailFragment: calling Fragment constructor caused an exception

caused by
java.lang.IllegalStateException: Fragment DetailFragment{f172e1b} (89c2cac6-2fcc-45ba-993c-e955b8a8fd6f) has null arguments

我认为 onBindViewHolder 在 Fragment 的 onClick 执行之前没有执行，或者出现问题，所以 bind.apply { _position = position } 不起作用。因此，_position 未设置，Safe Args 不起作用并导致上述异常。

源码如下：

package info.shutterpress.idols

import android.content.res.TypedArray
import android.os.Bundle
import android.view.LayoutInflater
import android.view.View
import android.view.ViewGroup
import android.widget.ImageView
import android.widget.TextView
import androidx.databinding.DataBindingUtil
import androidx.fragment.app.Fragment
import androidx.navigation.findNavController
import androidx.recyclerview.widget.RecyclerView
import info.shutterpress.idols.databinding.FragmentRecyclerviewBinding

class ListFragment : Fragment() {
    lateinit var bind: FragmentRecyclerviewBinding
    var title: Array<String>? = null
    var image: TypedArray? = null
    var _position: Int = 0

    override fun onCreateView(inflater: LayoutInflater, container: ViewGroup?, savedInstanceState: Bundle?): View? {
        super.onCreateView(inflater, container, savedInstanceState)
        bind = DataBindingUtil.inflate(inflater, R.layout.fragment_recyclerview, container, false)
        title = resources.getStringArray(R.array.idols_title_array)
        image = resources.obtainTypedArray(R.array.idols_list_image_array)
        var adapter = IdolsListAdapter(image, title)
        bind.idolsList.adapter = adapter
        return bind.root
    }

    inner class ListHolder(view: View) : RecyclerView.ViewHolder(view), View.OnClickListener {
        var titleTextView: TextView = view.findViewById(R.id.detail_item_title)
        var imageView: ImageView = view.findViewById(R.id.detail_item_image)

        init {
            view.setOnClickListener(this)
        }

        override fun onClick(v: View) {
            val action = ListFragmentDirections.actionRecyclerviewFragmentToDetailFragment().setPositionDatum(_position)
            v.findNavController().navigate(action)
        }

        fun bind(position: Int) {
            _position = position
        }
    }

    inner class IdolsListAdapter(var image: TypedArray?, var title: Array<String>?) : RecyclerView.Adapter<ListHolder>() {
        override fun onCreateViewHolder(parent: ViewGroup, viewType: Int) : ListHolder {
            val view = layoutInflater.inflate(R.layout.item_view, parent, false)
            return ListHolder(view)
        }

        override fun getItemCount() = title!!.size

        override fun onBindViewHolder(holder: ListHolder, position: Int) {
            var mImage = image!!.getResourceId(position, -1)
            var mTitle = title!![position]
            holder.apply {
                titleTextView.text = mTitle
                imageView.setImageResource(mImage)
            }
            holder.bind(_position)
        }
    }
}

XML：

<?xml version="1.0" encoding="utf-8"?>
<navigation 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:id="@+id/nav_main"
    app:startDestination="@id/main_fragment">

    <fragment
        android:id="@+id/main_fragment"
        android:name="info.shutterpress.idols.MainFragment"
        tools:layout="@layout/fragment_main">
        <action
            android:id="@+id/action_main_fragment_to_recyclerview_fragment"
            app:destination="@id/recyclerview_fragment" />
    </fragment>
    <fragment
        android:id="@+id/recyclerview_fragment"
        android:name="info.shutterpress.idols.ListFragment"
        tools:layout="@layout/fragment_recyclerview">
        <action
            android:id="@+id/action_recyclerview_fragment_to_detail_fragment"
            app:destination="@id/detail_fragment" />
    </fragment>
    <fragment
        android:id="@+id/detail_fragment"
        android:name="info.shutterpress.idols.DetailFragment"
        tools:layout="@layout/fragment_detail">
        <argument
            android:name="positionDatum"
            app:argType="integer"
            android:defaultValue="0" />
    </fragment>
</navigation>

如何使用 ListHolder 中的 onClick 函数将位置和 Int 数据发送给它？

Answer 1

尝试使用 click 监听器或使用 lamba 监听器。将侦听器从 ListFragment 传递到 IdolsListAdapter。单击事件将传递给片段，您可以在其中导航到具有位置的 DetailFragment

例如：

inner class IdolsListAdapter(var image: TypedArray?, var title: Array<String>?) : RecyclerView.Adapter<ListHolder>() {
        
        var clickListener: (Int) -> Unit = {}

        // other code

        override fun onBindViewHolder(holder: ListHolder, position: Int) {
            var mImage = image!!.getResourceId(position, -1)
            var mTitle = title!![position]
            holder.apply {
                titleTextView.text = mTitle
                imageView.setImageResource(mImage)
            }
            holder.bind(_position)
            holder.itemView.setOnClickListener {
                 clickListener(position)
            }
        }
    }

在片段中：

 override fun onCreateView(inflater: LayoutInflater, container: ViewGroup?, savedInstanceState: Bundle?): View? {
        super.onCreateView(inflater, container, savedInstanceState)
        // other code
        var adapter = IdolsListAdapter(image, title).apply {
            clickListener = { position -> navigateToDetailFragment(position) }
        }
        bind.idolsList.adapter = adapter
        return bind.root
    }
 
 fun navigateToDetailFragment(position: Int) {
      val action = ListFragmentDirections.actionRecyclerviewFragmentToDetailFragment().setPositionDatum(position)
      v.findNavController().navigate(action)
}