"想做什么"
在同一Activity中打开多个导航页面（drawerlayout）。
一个是从工具栏和其他是从按下正常按钮。我已经知道**OpenDrawer（GravityCompat.Start）;**帮助打开导航页面从按下按钮。因此，我正在寻找的方式打开多个导航页面在同一活动。

设定

创建一个带有默认导航的项目。
"我所做的一切"
将activity_main.xml的布局从DrawerLayout更改为FrameLayout，并在我制作的FrameLayout中制作了2个DrawerLayout。
此外，我在app_bar_main.xml中又创建了一个工具栏。
※文件的名称是默认的，我做了一个项目。

代码

activity_main.xml

<?xml version="1.0" encoding="utf-8"?>
<FrameLayout 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/frame_drawer"
                                    android:layout_width="match_parent"
                                    android:layout_height="match_parent">

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

    <include
        layout="@layout/app_bar_main"
        android:layout_width="match_parent"
        android:layout_height="match_parent" />

    <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"
        android:fitsSystemWindows="true"
        app:menu="@menu/activity_main_drawer" />

</androidx.drawerlayout.widget.DrawerLayout>

    <androidx.drawerlayout.widget.DrawerLayout
         android:layout_width="match_parent"
         android:layout_height="match_parent"
         android:id="@+id/drawer_layout2"
         android:fitsSystemWindows="true"
         tools:openDrawer="start">

    <include
        layout="@layout/app_bar_main"
        android:layout_width="match_parent"
        android:layout_height="match_parent" />

    <com.google.android.material.navigation.NavigationView
        android:id="@+id/nav_view2"
        android:layout_width="wrap_content"
        android:layout_height="match_parent"
        android:layout_gravity="start"
        android:fitsSystemWindows="true"
        app:menu="@menu/activity_main_drawer" />

</androidx.drawerlayout.widget.DrawerLayout>
</FrameLayout>

app_bar_main.xml

<?xml version="1.0" encoding="utf-8"?>
<androidx.coordinatorlayout.widget.CoordinatorLayout 
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">

<com.google.android.material.appbar.AppBarLayout
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:theme="@style/AppTheme.AppBarOverlay">

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

                <androidx.appcompat.widget.Toolbar
        android:id="@+id/toolbar"
        android:layout_width="match_parent"
        android:layout_height="?attr/actionBarSize"
        android:background="?attr/colorPrimary"
        app:popupTheme="@style/AppTheme.PopupOverlay" />

                <androidx.appcompat.widget.Toolbar
        android:id="@+id/toolbar2"
        android:layout_width="match_parent"
        android:layout_height="?attr/actionBarSize"
        android:background="?attr/colorPrimary"
        app:popupTheme="@style/AppTheme.PopupOverlay" />

</com.google.android.material.appbar.AppBarLayout>

<include layout="@layout/content_main" />

<com.google.android.material.floatingactionbutton.FloatingActionButton
    android:id="@+id/fab"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_gravity="bottom|end"
    android:layout_margin="@dimen/fab_margin"
    app:srcCompat="@android:drawable/ic_dialog_email" />

</androidx.coordinatorlayout.widget.CoordinatorLayout>

MainActivity.cs

[Activity(Label = "@string/app_name", Theme = "@style/AppTheme.NoActionBar", MainLauncher = true)]
public class MainActivity : AppCompatActivity, NavigationView.IOnNavigationItemSelectedListener
{
    DrawerLayout drawer2;
    protected override void OnCreate(Bundle savedInstanceState)
    {
        base.OnCreate(savedInstanceState);
        Xamarin.Essentials.Platform.Init(this, savedInstanceState);
        SetContentView(Resource.Layout.activity_main);
        Toolbar toolbar = FindViewById<Toolbar>(Resource.Id.toolbar);
        SetSupportActionBar(toolbar);
        SupportActionBar.Title = "Site 1";
        // for opening one more navigation page
        Toolbar toolbar2 = FindViewById<Toolbar>(Resource.Id.toolbar);
        SetSupportActionBar(toolbar2);
        SupportActionBar.Title = "Site 2";

        // for opening one more navigation page
        FloatingActionButton fab = FindViewById<FloatingActionButton>(Resource.Id.fab);
        fab.Click += FabOnClick;

        DrawerLayout drawer = FindViewById<DrawerLayout>(Resource.Id.drawer_layout);
        ActionBarDrawerToggle toggle = new ActionBarDrawerToggle(this, drawer, toolbar, Resource.String.navigation_drawer_open, Resource.String.navigation_drawer_close);
        drawer.AddDrawerListener(toggle);
        toggle.SyncState();
        NavigationView navigationView = FindViewById<NavigationView>(Resource.Id.nav_view);
        navigationView.SetNavigationItemSelectedListener(this);
        // for opening one more navigation page
        drawer2 = FindViewById<DrawerLayout>(Resource.Id.drawer_layout2);
        ActionBarDrawerToggle toggle2 = new ActionBarDrawerToggle(this, drawer2, toolbar2, Resource.String.navigation_drawer_open, Resource.String.navigation_drawer_close);
        drawer2.AddDrawerListener(toggle2);
        toggle2.SyncState();
        NavigationView navigationView2 = FindViewById<NavigationView>(Resource.Id.nav_view2);
        navigationView2.SetNavigationItemSelectedListener(this);
    }
        private void FabOnClick(object sender, EventArgs eventArgs)
        {
            drawer2.OpenDrawer(GravityCompat.Start);
        }
}