void LoadFragment(int id)
{
    Android.Support.V4.App.Fragment fragment = null;
    switch (id)
    {
        case Resource.Id.navigation_chats:
            fragment = Fragment1.NewInstance();
            break;
        case Resource.Id.navigation_user:
            fragment = Fragment2.NewInstance();
            break;
        case Resource.Id.navigation_users:
            fragment = Fragment3.NewInstance();
            break;
    }

    if (fragment == null)
        return;

    SupportFragmentManager.BeginTransaction()
        .Replace(Resource.Id.container, fragment)
        .Commit();
}

 public override View OnCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState)
        {
            var ignored = base.OnCreateView(inflater, container, savedInstanceState);
            return inflater.Inflate(Resource.Layout.fragment1, null);
        }

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:orientation="vertical"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent"
    android:id="@+id/frame_page">
    <!--список пользователей-->
</LinearLayout>

public override View OnCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState)
        {
            var ignored = base.OnCreateView(inflater, container, savedInstanceState);
            View _view = inflater.Inflate(Resource.Layout.fragment1, null);
            LinearLayout _list_msg = FindViewById<LinearLayout>(_view.Id.frame_page);
            
            return _list_msg;


        }