导航抽屉的切换按钮不工作

Question

导航视图的切换按钮不起作用，但如果我从左滑动它会显示导航视图 导航视图的切换按钮不起作用，但如果我从左滑动它会显示导航视图

MainActivity.java

public class DashboardActivity extends AppCompatActivity {
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_dashboard);
        Toolbar toolbar = findViewById(R.id.toolbar);
        setSupportActionBar(toolbar);

        NavigationView nav = findViewById(R.id.nav_view);
        DrawerLayout drawerLayout = findViewById(R.id.drawer);
        ActionBarDrawerToggle toggle = new ActionBarDrawerToggle(this, drawerLayout, toolbar, R.string.navigation_drawer_open, R.string.navigation_drawer_close);
        drawerLayout.addDrawerListener(toggle);
        toggle.syncState();
    }
}

MainActivity.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:id="@+id/drawer"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".MainActivity"
    android:fitsSystemWindows="true"
    tools:openDrawer="start">
    <RelativeLayout
        android:layout_width="wrap_content"
        android:layout_height="wrap_content">
        <androidx.appcompat.widget.Toolbar
            android:id="@+id/toolbar"
            android:background="#2f4475"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:gravity="start"
            app:title="ToolBar" />
    </RelativeLayout>

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

    <ScrollView
        android:layout_width="match_parent"
        android:layout_height="match_parent">

        <TextView
            android:id="@+id/textView"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_gravity="center"
            android:text="welcome"
            android:textSize="40sp" />
    </ScrollView>

</androidx.drawerlayout.widget.DrawerLayout>