Android studio 尝试显示其他活动时出现NullPointerException错误

错误是：

E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.example.aplicativostartup, PID: 9927
java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.aplicativostartup/com.example.aplicativostartup.MainActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.Button.setOnClickListener(android.view.View$OnClickListener)' on a null object reference
    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:3488)
    at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3635)
    at android.app.servertransaction.LaunchActivityItem.execute(LaunchActivityItem.java:83)
    at android.app.servertransaction.TransactionExecutor.executeCallbacks(TransactionExecutor.java:135)
    at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:95)
    at android.app.ActivityThread$H.handleMessage(ActivityThread.java:2175)
    at android.os.Handler.dispatchMessage(Handler.java:107)
    at android.os.Looper.loop(Looper.java:237)
    at android.app.ActivityThread.main(ActivityThread.java:7860)
    at java.lang.reflect.Method.invoke(Native Method)
    at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:493)
    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1075)
 Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.Button.setOnClickListener(android.view.View$OnClickListener)' on a null object reference
    at com.example.aplicativostartup.MainActivity.onCreate(MainActivity.java:55)
    at android.app.Activity.performCreate(Activity.java:7955)
    at android.app.Activity.performCreate(Activity.java:7944)
    at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1307)
    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:3463)
    at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3635) 
    at android.app.servertransaction.LaunchActivityItem.execute(LaunchActivityItem.java:83) 
    at android.app.servertransaction.TransactionExecutor.executeCallbacks(TransactionExecutor.java:135) 
    at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:95) 
    at android.app.ActivityThread$H.handleMessage(ActivityThread.java:2175) 
    at android.os.Handler.dispatchMessage(Handler.java:107) 
    at android.os.Looper.loop(Looper.java:237) 
    at android.app.ActivityThread.main(ActivityThread.java:7860) 
    at java.lang.reflect.Method.invoke(Native Method) 
    at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:493) 
    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1075) 

主要活动：

package com.example.aplicativostartup;

import android.content.Intent;
import android.os.Bundle;
import android.view.View;
import android.view.Menu;
import android.widget.Button;

import com.example.aplicativostartup.ui.gallery.ListaActivity;
import com.google.android.material.floatingactionbutton.FloatingActionButton;
import com.google.android.material.snackbar.Snackbar;
import com.google.android.material.navigation.NavigationView;

import androidx.navigation.NavController;
import androidx.navigation.Navigation;
import androidx.navigation.ui.AppBarConfiguration;
import androidx.navigation.ui.NavigationUI;
import androidx.drawerlayout.widget.DrawerLayout;
import androidx.appcompat.app.AppCompatActivity;
import androidx.appcompat.widget.Toolbar;

public class MainActivity extends AppCompatActivity {

private AppBarConfiguration mAppBarConfiguration;
/* private Button buttonFrios;
private Button buttonMassas;
private Button buttonHigiene;*/




@Override
protected void onCreate(Bundle savedInstanceState) {

    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    Toolbar toolbar = findViewById(R.id.toolbar);
    setSupportActionBar(toolbar);
    FloatingActionButton fab = findViewById(R.id.fab);
    fab.setOnClickListener(view -> Snackbar.make(view, "Replace with your own action", Snackbar.LENGTH_LONG)
            .setAction("Action", null).show());
    DrawerLayout drawer = findViewById(R.id.drawer_layout);
    NavigationView navigationView = findViewById(R.id.nav_view);
    // Passing each menu ID as a set of Ids because each
    // menu should be considered as top level destinations.
    mAppBarConfiguration = new AppBarConfiguration.Builder(
            R.id.nav_home, R.id.nav_gallery, R.id.nav_slideshow)
            .setDrawerLayout(drawer)
            .build();
    NavController navController = Navigation.findNavController(this, R.id.nav_host_fragment);
    NavigationUI.setupActionBarWithNavController(this, navController, mAppBarConfiguration);
    NavigationUI.setupWithNavController(navigationView, navController);

    Button ButtonCarnes = findViewById(R.id.ButtonCarnes);
    ButtonCarnes.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View view) {
            Intent intent = new Intent(getApplicationContext(), ListaActivity.class);
            startActivity(intent);
        }
    });
}

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

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

我在AndroidStudio中做这个项目只是作为旁注，我真的需要帮助

按钮的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=".ui.gallery.GalleryFragment">

<Button
    android:id="@+id/ButtonCarnes"
    android:layout_width="210dp"
    android:layout_height="50dp"
    android:layout_marginBottom="4dp"
    android:text="carnes"
    app:layout_constraintBottom_toTopOf="@+id/buttonFrios"
    app:layout_constraintStart_toStartOf="parent"
    app:layout_constraintTop_toTopOf="parent"
    app:layout_constraintVertical_chainStyle="packed" />

<Button
    android:id="@+id/buttonFrios"
    android:layout_width="210dp"
    android:layout_height="50dp"
    android:layout_marginBottom="4dp"
    android:text="frios"
    app:layout_constraintBottom_toTopOf="@+id/buttonMassas"
    app:layout_constraintStart_toStartOf="parent"
    app:layout_constraintTop_toBottomOf="@+id/ButtonCarnes" />

<Button
    android:id="@+id/buttonMassas"
    android:layout_width="210dp"
    android:layout_height="50dp"
    android:layout_marginBottom="4dp"
    android:text="massas"
    app:layout_constraintBottom_toTopOf="@+id/buttonHigiene"
    app:layout_constraintStart_toStartOf="parent"
    app:layout_constraintTop_toBottomOf="@+id/buttonFrios" />

<Button
    android:id="@+id/buttonHigiene"
    android:layout_width="210dp"
    android:layout_height="50dp"
    android:layout_marginBottom="452dp"
    android:text="higiene"
    app:layout_constraintBottom_toBottomOf="parent"
    app:layout_constraintStart_toStartOf="parent"
    app:layout_constraintTop_toBottomOf="@+id/buttonMassas" />

<ImageView
    android:id="@+id/imageView3"
    android:layout_width="201dp"
    android:layout_height="50dp"
    android:layout_marginBottom="4dp"
    android:scaleType="centerCrop"
    android:src="@drawable/carnes"
    app:layout_constraintBottom_toTopOf="@+id/imageView4"
    app:layout_constraintEnd_toEndOf="parent"
    app:layout_constraintTop_toTopOf="parent"
    app:layout_constraintVertical_chainStyle="packed" />

<androidx.constraintlayout.widget.Guideline
    android:id="@+id/guideline"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:orientation="vertical" />

<ImageView
    android:id="@+id/imageView4"
    android:layout_width="201dp"
    android:layout_height="50dp"
    android:layout_marginBottom="4dp"
    android:scaleType="centerCrop"
    android:src="@drawable/frios"
    app:layout_constraintBottom_toTopOf="@+id/imageView5"
    app:layout_constraintEnd_toEndOf="parent"
    app:layout_constraintTop_toBottomOf="@+id/imageView3" />

<ImageView
    android:id="@+id/imageView5"
    android:layout_width="201dp"
    android:layout_height="50dp"
    android:layout_marginBottom="4dp"
    android:scaleType="centerCrop"
    android:src="@drawable/massas"
    app:layout_constraintBottom_toTopOf="@+id/imageView6"
    app:layout_constraintEnd_toEndOf="parent"
    app:layout_constraintTop_toBottomOf="@+id/imageView4" />

<ImageView
    android:id="@+id/imageView6"
    android:layout_width="201dp"
    android:layout_height="50dp"
    android:layout_marginBottom="452dp"
    android:scaleType="centerCrop"
    android:src="@drawable/unnamed"
    app:layout_constraintBottom_toBottomOf="parent"
    app:layout_constraintEnd_toEndOf="parent"
    app:layout_constraintTop_toBottomOf="@+id/imageView5" />
</androidx.constraintlayout.widget.ConstraintLayout>

程序甚至在打开之前就崩溃了，我得到了NullPointerException错误，我不知道我做错了什么，但我到处搜索它都说这是因为有一个null对象或类似的东西，但我对这方面还不熟悉，不知道这意味着什么，也不知道如何修复它