"想做什么"
我想在未与SetContentView链接的活动中获取android：id =“@+id/drawer_layout2”，因为我想使用按钮打开导航？DrawerLayout？。我已经知道drawer.OpenDrawer（GravityCompat.Start），但drawer为空。

关系

主要活动. cs-活动_主要. xml
NaviDrawer.cs -绘图文件. xml

错误消息

System.NullReferenceException: 'Object reference not set to an instance of an object.'

代码

主要活动

public class MainActivity : AppCompatActivity, NavigationView.IOnNavigationItemSelectedListener, TabLayout.IOnTabSelectedListener
{
    private Context context;
    DrawerLayout m_drawer;

protected override void OnCreate(Bundle savedInstanceState)
    {
        base.OnCreate(savedInstanceState);
        Xamarin.Essentials.Platform.Init(this, savedInstanceState);
        SetContentView(Resource.Layout.activity_main);
        context = this;

        m_drawer = FindViewById<DrawerLayout>(Resource.Id.drawer_layout2);

        btn_drawer = FindViewById<Button>(Resource.Id.btn_drawer);
        btn_drawer.Click += Btn_Drawer_Click;
    }

    private void Btn_Drawer_Click(object sender, EventArgs args)
    {
        m_drawer.OpenDrawer(GravityCompat.Start);
    }

Drawer.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_layout2"
                                    android:layout_width="match_parent"
                                    android:layout_height="match_parent"
                                    android:fitsSystemWindows="true"
                                    tools:openDrawer="start">

  <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">

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

        <TextView
            android:id="@+id/test"
            android:layout_width="match_parent"
            android:layout_height="58dp"
            android:text="test"
            android:textSize="12dp"
            android:gravity="center">
        </TextView>
    </LinearLayout>

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

</androidx.drawerlayout.widget.DrawerLayout>