具有从ObservableCollection派生的类的xaml中存在未知类型错误

基于MSDN上的这个例子，我创建了一个"从ObservableCollection派生的非通用自定义集合类，并将其约束为特定类型。"它用作listview控件的ItemsSource属性。这一切都很完美，xaml设计视图显示了我加载到自定义集合类中的示例数据。

当我试图构建项目时，问题就出现了；我收到此错误："错误1 XML命名空间'clr namespace:Messaging_2_0中的未知类型'ThreadCollection'；assembly=Messaging 2.0.WindowsPhone，Version=1.0.0.0，Culture=neutral，PublicKeyToken=null'C:''Users''Wesley''Source''Repos''Messenging2.0''Messaging 2.0''Messing 2.0''WindowsPhone''MainPage.xaml 14 10 Messaging 2.0.Windows Phone.

此错误源自下面xaml代码的<c:ThreadCollection x:Key="MainThreadCollection"/>行。

<Page
x:Class="Messaging_2._0.MainPage"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:local="using:Messaging_2._0"
xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
xmlns:c="clr-namespace:Messaging_2._0"
mc:Ignorable="d"
Background="{ThemeResource ApplicationPageBackgroundThemeBrush}">
<Page.Resources>
    <c:ThreadCollection x:Key="MainThreadCollection"/>
</Page.Resources>
<The code for the listview control is here, I haven't included it because it works as I expect.>

以下是xaml:引用的C#代码

using System;
using System.Collections.Generic;
using System.IO;
using System.Linq;
using System.Runtime.InteropServices.WindowsRuntime;
using Windows.Foundation;
using Windows.Foundation.Collections;
using Windows.UI.Xaml;
using Windows.UI.Xaml.Controls;
using Windows.UI.Xaml.Controls.Primitives;
using Windows.UI.Xaml.Data;
using Windows.UI.Xaml.Input;
using Windows.UI.Xaml.Media;
using Windows.UI.Xaml.Navigation;
using System.Collections.ObjectModel;
// The Blank Page item template is documented at http://go.microsoft.com/fwlink/?LinkId=234238
namespace Messaging_2._0
{
    /// <summary>
    /// An empty page that can be used on its own or navigated to within a Frame.
    /// </summary>
    public sealed partial class MainPage : Page
    {
        public ThreadCollection MainThreadCollection = new ThreadCollection();
        public MainPage()
        {
            this.InitializeComponent();
            this.NavigationCacheMode = NavigationCacheMode.Required;
            this.DataContext = this;
        }
        /// <summary>
        /// Invoked when this page is about to be displayed in a Frame.
        /// </summary>
        /// <param name="e">Event data that describes how this page was reached.
        /// This parameter is typically used to configure the page.</param>
        protected override void OnNavigatedTo(NavigationEventArgs e)
        {
            // TODO: Prepare page for display here.
            // TODO: If your application contains multiple pages, ensure that you are
            // handling the hardware Back button by registering for the
            // Windows.Phone.UI.Input.HardwareButtons.BackPressed event.
            // If you are using the NavigationHelper provided by some templates,
            // this event is handled for you.
        }
        private void AddThread(object sender, RoutedEventArgs e)
        {
            MainThreadCollection.Add(new ThreadViewItem() { Name = "Tom Riddle", LatestMessage = "It worked!" });
        }
    }
    public class ThreadCollection : ObservableCollection<ThreadViewItem>
    {
        public ThreadCollection()
            : base()
        {
            Add(new ThreadViewItem() { Name = "Harry Potter", LatestMessage = "What's up?" });
        }
    }
    public class ThreadViewItem
    {
        public String Name
        {
            get;
            set;
        }
        public String LatestMessage
        {
            get;
            set;
        }
    }
}

因为设计视图正确地预览了哈利波特的信息，我认为问题相对较小，我只是不知道它到底是什么。