View Binding无法解析textview_first ID的问题求助

我是个编程新手，现在碰到一个头疼的问题：下面这行代码还没等我运行程序，IDE就直接报“cannot find symbol”错误，说textviewFirst是未知的：

TextView textView = binding.textviewFirst;

以下是我的MainActivity.java完整代码：

package com.example.rp;

import android.os.Bundle;

import com.google.android.material.snackbar.Snackbar;

import androidx.appcompat.app.AppCompatActivity;

import android.view.View;

import androidx.navigation.NavController;
import androidx.navigation.Navigation;
import androidx.navigation.ui.AppBarConfiguration;
import androidx.navigation.ui.NavigationUI;

import com.example.rp.databinding.ActivityMainBinding;

import android.view.Menu;
import android.view.MenuItem;

import com.example.rp.ApiService;
import com.example.rp.Post;

import java.util.List;

import retrofit2.Retrofit;  // Import Retrofit
import retrofit2.converter.gson.GsonConverterFactory;

import retrofit2.Call;  // Import Call
import retrofit2.Callback;  // Import Callback
import retrofit2.Response;  // Import Response

import android.widget.TextView;

public class MainActivity extends AppCompatActivity {

    private AppBarConfiguration appBarConfiguration;
    private ActivityMainBinding binding;
    private TextView textView;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);

        binding = ActivityMainBinding.inflate(getLayoutInflater());
        setContentView(binding.getRoot());
        //TextView textView = findViewById(R.id.textview_first);
        TextView textView = binding.textviewFirst;
        setSupportActionBar(binding.toolbar);

        NavController navController = Navigation.findNavController(this, R.id.nav_host_fragment_content_main);
        appBarConfiguration = new AppBarConfiguration.Builder(navController.getGraph()).build();
        NavigationUI.setupActionBarWithNavController(this, navController, appBarConfiguration);

        binding.fab.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                Snackbar.make(view, "Replace with your own action", Snackbar.LENGTH_LONG)
                        .setAnchorView(R.id.fab)
                        .setAction("Action", null).show();
            }
        });

        Retrofit retrofit = new Retrofit.Builder()
                .baseUrl("https://jsonplaceholder.typicode.com/")  // Base URL
                .addConverterFactory(GsonConverterFactory.create())  // Gson converter for JSON parsing
                .build();

// Create the API service instance
        ApiService apiService = retrofit.create(ApiService.class);

// Make the network request
        Call<List<Post>> call = apiService.getPosts();

// Execute the call (synchronously for simplicity here)
        call.enqueue(new Callback<List<Post>>() {
            @Override
            public void onResponse(Call<List<Post>> call, Response<List<Post>> response) {
                if (response.isSuccessful()) {
                    List<Post> posts = response.body();  // Get the list of users
                    try {
                        textView.setText(posts.toString());

                    } catch (Exception e) {
                        e.printStackTrace();
                    }
                    //
                    // Handle the response here
                }
            }

            @Override
            public void onFailure(Call<List<Post>> call, Throwable t) {
                // Handle failure
            }
        });
    }

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        // Inflate the menu; this adds items to the action bar if it is present.
        getMenuInflater().inflate(R.menu.menu_main, menu);
        return true;
    }

    @Override
    public boolean onOptionsItemSelected(MenuItem item) {
        // Handle action bar item clicks here. The action bar will
        // automatically handle clicks on the Home/Up button, so long
        // as you specify a parent activity in AndroidManifest.xml.
        int id = item.getItemId();

        //noinspection SimplifiableIfStatement
        if (id == R.id.action_settings) {
            return true;
        }

        return super.onOptionsItemSelected(item);
    }

    @Override
    public boolean onSupportNavigateUp() {
        NavController navController = Navigation.findNavController(this, R.id.nav_host_fragment_content_main);
        return NavigationUI.navigateUp(navController, appBarConfiguration)
                || super.onSupportNavigateUp();
    }
}

这个出问题的TextView是定义在fragment_first.xml布局文件里的，代码如下：

<?xml version="1.0" encoding="utf-8"?>
<androidx.core.widget.NestedScrollView 
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=".FirstFragment">

<androidx.constraintlayout.widget.ConstraintLayout
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:padding="16dp">

    <Button
        android:id="@+id/button_first"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="@string/next"
        app:layout_constraintBottom_toTopOf="@id/textview_first"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent" />

    <TextView
        android:id="@+id/textview_first"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginTop="16dp"
        android:text="@string/lorem_ipsum"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toBottomOf="@id/button_first" />
</androidx.constraintlayout.widget.ConstraintLayout>
</androidx.core.widget.NestedScrollView>

特别奇怪的是，如果我换成findViewById的方式来获取这个TextView，IDE就能正常识别这个ID，代码完全没问题：

//TextView textView = findViewById(R.id.textview_first);

备注：内容来源于stack exchange，提问作者Anunnaki Priest