即使SelectedAssembly被重写，也找不到ViewModel的视图

由于某种原因，我得到了Cannot find view for CaliburnPractice.ViewModel错误。我已经看了这里的一些答案，但没有一个对我有效。我已经将视图和视图模型放在单独的命名文件夹中，并且已经覆盖了SelectedAssembly方法。发生了什么事？请参阅下面的代码。

ViewModel.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using Caliburn.Micro;
namespace CaliburnPractice
{
    public class ViewModel : PropertyChangedBase
   {
   }
}

应用程序xaml

<Application x:Class="CaliburnPractice.App"
         xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
         xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
         xmlns:local="clr-namespace:CaliburnPractice"
         >
<Application.Resources>
    <ResourceDictionary>
        <ResourceDictionary.MergedDictionaries>
            <ResourceDictionary>
                <local:Bootstrapper x:Key="bootstrapper" />
            </ResourceDictionary>
        </ResourceDictionary.MergedDictionaries>
    </ResourceDictionary>
</Application.Resources>

实践视图.xaml

<UserControl x:Class="CaliburnPractice.PracticeView"
         xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
         xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
         xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006" 
         xmlns:d="http://schemas.microsoft.com/expression/blend/2008" 
         mc:Ignorable="d" 
         d:DesignHeight="300" d:DesignWidth="300">
<Grid Width="300" Height="300" Background="LightBlue">
</Grid>

引导程序.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using Caliburn.Micro;
using System.Reflection;
namespace CaliburnPractice
{
    public class Bootstrapper : BootstrapperBase
    {
        public Bootstrapper()
        {
            Initialize();
        }
        protected override void OnStartup(object sender,         System.Windows.StartupEventArgs e)
        {
            base.OnStartup(sender, e);
            DisplayRootViewFor<ViewModel>();
        }
        protected override IEnumerable<System.Reflection.Assembly>     SelectAssemblies()
        {
            return new[]
            {
                Assembly.GetExecutingAssembly()
            };
        }
    }
}