無法從RecyclerView配接器啟動Fragment

在 RecyclerView 配接器中有一個 NameListHolder 類的代碼

class NameListHolder(val binding: NameListItemBinding) : RecyclerView.ViewHolder(binding.root) {

    fun bind(paginationLocalModel: PaginationLocalModel, position: Int, context: NameListFragment){

        binding.name.text = paginationLocalModel.name
        itemView.setOnClickListener{

            val fragment = DescriptionFragment()
            val bundle = Bundle()
            bundle.putInt("position", position)
            fragment.setArguments(bundle)

            val activity=context.context as AppCompatActivity
            activity.supportFragmentManager
                .beginTransaction()
                .replace(R.id.rd_fragment, fragment)
                .commitNow()

            Log.d("OnClick", "произошло нажатие по позиции $position")
        }

    }

}

片段內部itemView.setOnClickListener應該觸發，但是當我單擊串列項時，NullPointerException會拋出 a：

E/AndroidRuntime: FATAL EXCEPTION: main
    Process: com.sem.receivedata, PID: 5484
    java.lang.NullPointerException
        at com.sem.receivedata.presentation.DescriptionFragment.<init>(DescriptionFragment.kt:22)
        at com.sem.receivedata.presentation.adapters.NameListAdapter$NameListHolder.bind$lambda-0(NameListAdapter.kt:49)
        at com.sem.receivedata.presentation.adapters.NameListAdapter$NameListHolder.$r8$lambda$FuXGFWDKhm2ZD3YhtF7Xh98aUvc(Unknown Source:0)
        at com.sem.receivedata.presentation.adapters.NameListAdapter$NameListHolder$$ExternalSyntheticLambda0.onClick(Unknown Source:4)

DescriptionFragment.kt:22指向片段val position: Int = bundle!!.getInt("position", 0)內的字串DescriptionFragment

NameListAdapter.kt:49指向val fragment = DescriptionFragment()里面的線NameListHolder

Unknown Source:0并且Unknown Source:4始終指向第 0 行和第 4 行，無論那里有什么（在newInstance()匯入之前）

整個資料鏈：

NameListFragment：

class NameListFragment : Fragment() {

...

    private fun initRecyclerExchangeRate(){
    
        binding?.listNameRV?.layoutManager =
            LinearLayoutManager(context)
        nameListAdapter = NameListAdapter(this)
    
        binding?.listNameRV?.adapter = nameListAdapter
    }

...

}

NameListAdapter：

class NameListAdapter(var context: NameListFragment
) : RecyclerView.Adapter<NameListAdapter.NameListHolder>() {

...

    override fun onBindViewHolder(holder: NameListHolder, position: Int) {
        holder.bind(pagination[position], position, context)
    }

...


    class NameListHolder(val binding: NameListItemBinding) : RecyclerView.ViewHolder(binding.root) {
    
        fun bind(paginationLocalModel: PaginationLocalModel, position: Int, context: NameListFragment){
    
            binding.name.text = paginationLocalModel.name
            itemView.setOnClickListener{
    
                val fragment = DescriptionFragment()
                val bundle = Bundle()
                bundle.putInt("position", position)
                fragment.setArguments(bundle)
    
                val activity=context.context as AppCompatActivity
                activity.supportFragmentManager
                    .beginTransaction()
                    .replace(R.id.rd_fragment, fragment)
                    .commitNow()
    
                Log.d("OnClick", "произошло нажатие по позиции $position")
            }
    
        }
    
    }

...

}

DescriptionFragment：

class DescriptionFragment : Fragment() {

...

    val bundle: Bundle? = this.getArguments();
    val position: Int = bundle!!.getInt("position", 0)

...

}

從 Activity 啟動第一個片段是在標記內完成的：

<?xml version="1.0" encoding="utf-8"?>
<layout 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"
    tools:context=".presentation.MainActivity">

    <androidx.constraintlayout.widget.ConstraintLayout
        android:layout_width="match_parent"
        android:layout_height="match_parent">

    <androidx.appcompat.widget.LinearLayoutCompat
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:orientation="vertical">

        <FrameLayout
            android:id="@ id/framelayout"
            xmlns:android="http://schemas.android.com/apk/res/android"
            android:layout_width="match_parent"
            android:layout_height="match_parent" >

            <fragment
                android:id="@ id/rd_fragment"
                android:name="com.sem.receivedata.presentation.NameListFragment"
                android:layout_width="match_parent"
                android:layout_height="match_parent" />



        </FrameLayout>

    </androidx.appcompat.widget.LinearLayoutCompat>

    </androidx.constraintlayout.widget.ConstraintLayout>

</layout>

uj5u.com熱心網友回復：

您正在此行中創建新片段

val fragment = DescriptionFragment()

所以它被創建并在開始時嘗試決議包

val bundle: Bundle? = this.getArguments();
val position: Int = bundle!!.getInt("position", 0)

尚未設定，您將在Fragment創建后的下一行執行此操作。但是您一開始就被迫從 bundle ( !!) 中讀取，就null在此時，所以NullPointerException發生了

您的方法是錯誤的，您應該在某些生命周期方法中讀取引數，例如onCreateor onCreateView，當您Fragment創建、設定（例如Bundle引數集）、添加到布局和運行時（因為它正在呼叫生命周期方法）

標籤：安卓 科特林 安卓片段 android-recyclerview 空指针异常

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