我正在尝试用碎片创建导航抽屉。我想在下一个片段中隐藏/删除工具栏。我想要没有工具栏的完整的空片段。但每当我尝试我的导航抽屉不起作用。我想要带工具栏+导航抽屉的前三页菜单（片段）和带导航抽屉的下两个片段活动（不包括工具栏）

Below is my code activity_main.xml <?xml version="1.0" encoding="utf-8"?>

<androidx.drawerlayout.widget.DrawerLayout
    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"
    android:id="@+id/drawer_layout"
    android:fitsSystemWindows="true"
    tools:context=".MainActivity"
    tools:openDrawer="start">

<LinearLayout
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical">

    <androidx.appcompat.widget.Toolbar
        android:id="@+id/toolbar"
        android:layout_width="match_parent"
        android:layout_height="?attr/actionBarSize"
        android:background="#ffffff"
        />
    <FrameLayout
        android:id="@+id/fragment_container"
        android:layout_width="match_parent"
        android:layout_height="match_parent">
    </FrameLayout>
</LinearLayout>
    <FrameLayout
        android:id="@+id/fragment_container2"
        android:layout_width="match_parent"
        android:layout_height="match_parent">
    </FrameLayout>

    <com.google.android.material.navigation.NavigationView
        android:layout_width="wrap_content"
        android:layout_height="match_parent"
        app:headerLayout="@layout/nav_header"
        app:menu="@menu/drawer_menu"
        android:id="@+id/nav_view"
        android:layout_gravity="start">

        </com.google.android.material.navigation.NavigationView>

</androidx.drawerlayout.widget.DrawerLayout>

这是mainactivity.java

package com.example.guvi;

    import androidx.annotation.NonNull;
    import androidx.appcompat.app.ActionBarDrawerToggle;
    import androidx.appcompat.app.AppCompatActivity;
    import androidx.appcompat.widget.Toolbar;
    import androidx.core.view.GravityCompat;
    import androidx.drawerlayout.widget.DrawerLayout;

    import android.annotation.SuppressLint;
    import android.content.Intent;
    import android.os.Bundle;
    import android.view.MenuItem;

    import com.google.android.material.navigation.NavigationView;

    public class MainActivity extends AppCompatActivity implements NavigationView.OnNavigationItemSelectedListener {

        private DrawerLayout drawer;
        Toolbar toolbar;

        @Override
        protected void onCreate(Bundle savedInstanceState) {
            super.onCreate(savedInstanceState);
           setContentView(R.layout.activity_main);

           toolbar = findViewById(R.id.toolbar);
           setSupportActionBar(toolbar);

           drawer = findViewById(R.id.drawer_layout);
           ActionBarDrawerToggle toggle = new ActionBarDrawerToggle(this, drawer, toolbar,R.string.navigation_drawer_open,R.string.navigation_drawer_close);
           drawer.addDrawerListener(toggle);
           toggle.syncState();

          this.setTitle("");
          getSupportFragmentManager().beginTransaction().replace(R.id.fragment_container,new CoursesFragment()).commit();

            NavigationView naview = findViewById(R.id.nav_view);
            naview.setNavigationItemSelectedListener(this);

        }

        @Override
        public void onBackPressed() {
            if (drawer.isDrawerOpen(GravityCompat.START)) {
                drawer.closeDrawer(GravityCompat.START);
            } else {
                super.onBackPressed();
            }
        }

        @SuppressLint("NonConstantResourceId")
        @Override
        public boolean onNavigationItemSelected(@NonNull MenuItem item) {

            switch (item.getItemId()){
                case R.id.nav_course:
                    getSupportFragmentManager().beginTransaction().replace(R.id.fragment_container,new CoursesFragment()).commit();
                    break;
                case R.id.nav_invfriends:
                    getSupportFragmentManager().beginTransaction().replace(R.id.fragment_container,new InviteFragment2()).commit();
                    break;
                case R.id.nav_contactus:
                    getSupportFragmentManager().beginTransaction().replace(R.id.fragment_container,new ContactFragment()).commit();
                    break;

            }

            drawer.closeDrawer(GravityCompat.START);

            return true;
        }

    }