Basic example

XML: Layout:

<?xml version="1.0" encoding="UTF-8" ?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:background="@color/colorGray"
   android:layout_width="fill_parent"
   android:layout_height="fill_parent"
   android:orientation="vertical">
   <include layout="@layout/search_container" />
</LinearLayout>

search_container.xml

<?xml version="1.0" encoding="UTF-8" ?>
<com.google.android.material.appbar.AppBarLayout
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:android="http://schemas.android.com/apk/res/android"
    android:id="@+id/toolbar_container"
    android:layout_width="match_parent"
    android:layout_height="wrap_content">

    <FrameLayout
        android:layout_width="match_parent"
        android:layout_height="wrap_content">

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

        <com.miguelcatalan.materialsearchview.MaterialSearchView
            android:id="@+id/search_view"
            android:layout_width="match_parent"
            android:layout_height="wrap_content" />
    </FrameLayout>

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

Menu: menu_search.xml

<?xml version="1.0" encoding="UTF-8" ?>
<menu 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"
    tools:context="com.domain.myApp.YourClassActivity">
    <item
        android:id="@+id/action_search"
        android:icon="@drawable/ic_action_action_search"
        android:orderInCategory="100"
        android:title="@string/search_title"
        app:showAsAction="always" />
</menu>

C#:

public partial class YourClassActivity : AppCompatActivity
{
    private MaterialSearchView SearchView;
    protected override void OnCreate(Bundle savedInstanceState)
    {

        SearchView = FindViewById<MaterialSearchView>(Resource.Id.search_view);

        SearchView.SetOnQueryTextListener(new MaterialSearchViewListener(this));

        //Optional to enable voice search
        //SearchView.SetVoiceSearch(true);        
    }

    public override bool OnCreateOptionsMenu(IMenu menu)
    {
        MenuInflater.Inflate(Resource.Menu.menu_search, menu);

        SearchView.SetMenuItem(menu.FindItem(Resource.Id.action_search));

        return true;
    }
}

public partial class YourClassActivity
{
    public class MaterialSearchViewListener : Java.Lang.Object, MaterialSearchView.IOnQueryTextListener
    {
        public bool OnQueryTextChange(string p0)
        {
            return true;
        }

        public bool OnQueryTextSubmit(string p0)
        {
            return true;
        }
    }
}