如何在Fragment类中访问RecyclerView内的TextView控件ID？

问题场景 #

我在Fragment布局里使用了RecyclerView，对应的子项布局XML包含tvTitle等TextView控件。尝试在Fragment类中直接访问该TextView以执行Fragment事务，编写了如下代码：

var titleTextView = view.findViewById<TextView>(R.id.tvTitle)

val subjectFragment = SubjectFragment()

println(titleTextView.text)

运行后触发空指针异常，报错日志如下：

E/AndroidRuntime: FATAL EXCEPTION: main
    Process: com.example.samachar, PID: 7038
    java.lang.NullPointerException: Attempt to invoke virtual method 'java.lang.CharSequence android.widget.TextView.getText()' on a null object reference
        at com.example.samachar.NewsFragment.onViewCreated(NewsFragment.kt:86)
        at androidx.fragment.app.Fragment.performViewCreated(Fragment.java:2987)
        at androidx.fragment.app.FragmentStateManager.createView(FragmentStateManager.java:546)
        at androidx.fragment.app.FragmentStateManager.moveToExpectedState(FragmentStateManager.java:282)
        at androidx.fragment.app.FragmentManager.executeOpsTogether(FragmentManager.java:2189)
        at androidx.fragment.app.FragmentManager.removeRedundantOperationsAndExecute(FragmentManager.java:2100)
        at androidx.fragment.app.FragmentManager.execPendingActions(FragmentManager.java:2002)
        at androidx.fragment.app.FragmentManager.dispatchStateChange(FragmentManager.java:3138)
        at androidx.fragment.app.FragmentManager.dispatchActivityCreated(FragmentManager.java:3072)
        at androidx.fragment.app.FragmentController.dispatchActivityCreated(FragmentController.java:251)
        at androidx.fragment.app.FragmentActivity.onStart(FragmentActivity.java:502)
        at androidx.appcompat.app.AppCompatActivity.onStart(AppCompatActivity.java:248)
        at android.app.Instrumentation.callActivityOnStart(Instrumentation.java:1435)
        at android.app.Activity.performStart(Activity.java:8024)
        at android.app.ActivityThread.handleStartActivity(ActivityThread.java:3475)
        at android.app.servertransaction.TransactionExecutor.performLifecycleSequence(TransactionExecutor.java:221)
        at android.app.servertransaction.TransactionExecutor.cycleToPath(TransactionExecutor.java:201)
        at android.app.servertransaction.TransactionExecutor.executeLifecycleState(TransactionExecutor.java:173)
        at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:97)
        at android.app.ActivityThread$H.handleMessage(ActivityThread.java:2066)
        at android.os.Handler.dispatchMessage(Handler.java:106)
        at android.os.Looper.loop(Looper.java:223)
        at android.app.ActivityThread.main(ActivityThread.java:7656)
        at java.lang.reflect.Method.invoke(Native Method)
        at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:592)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:947)
I/Process: Sending signal. PID: 7038 SIG: 9

我的目标是通过FragmentManager执行事务切换布局：

// var fragment = parentFragmentManager?.beginTransaction()
// fragment?.replace(R.id.newsFrameLayout, subjectFragment)
// fragment?.commit()

但始终无法在Fragment类中直接访问到RecyclerView子项里的TextView控件。

RecyclerView子项的XML布局文件：

<?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:id="@+id/newsItem"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:paddingHorizontal="16dp"
    android:paddingVertical="12dp">

    <TextView
        android:id="@+id/tvTitle"
        android:layout_width="0dp"
        android:layout_height="wrap_content"
        android:text="@string/title_eg"
        android:textColor="@color/purple_200"
        android:textSize="14sp"
        android:textStyle="bold"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent" />

    <TextView
        android:id="@+id/tvDescription"
        android:layout_width="0dp"
        android:layout_height="wrap_content"
        android:text="@string/description_eg"
        android:textSize="12sp"
        android:textColor="@color/black"
        android:maxLines="2"
        android:justificationMode="inter_word"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toBottomOf="@+id/tvTitle" />

    <TextView
        android:id="@+id/tvCategory"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:background="@color/teal_700"
        android:padding="2dp"
        android:text="@string/category_eg"
        android:textColor="@color/white"
        android:textSize="10sp"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toBottomOf="@+id/tvDescription" />

    <TextView
        android:id="@+id/tvPublishedDate"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="@string/pub_date_eg"
        android:textSize="10sp"
        app:layout_constraintBottom_toBottomOf="@+id/tvCategory"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintTop_toBottomOf="@+id/tvDescription" />

</androidx.constraintlayout.widget.ConstraintLayout>

解决方法 #

在RecyclerView的Adapter类的onBindViewHolder方法中，为tvTitle设置点击事件，并通过控件的上下文获取Activity实例，调用supportFragmentManager执行Fragment事务。示例代码如下：

override fun onBindViewHolder(holder: ViewHolder, position: Int) {
    val item = dataList[position]
    holder.titleTextView.text = item.title

    holder.titleTextView.setOnClickListener {
        val subjectFragment = SubjectFragment()
        // 通过控件上下文获取Activity并执行Fragment事务
        (holder.itemView.context as AppCompatActivity).supportFragmentManager.beginTransaction()
            .replace(R.id.newsFrameLayout, subjectFragment)
            .commit()
    }
}

// ViewHolder定义示例
class ViewHolder(itemView: View) : RecyclerView.ViewHolder(itemView) {
    val titleTextView: TextView = itemView.findViewById(R.id.tvTitle)
}

内容的提问来源于stack exchange，提问作者Unish Raj.