加载的事件不会在用户控件中触发

我有一个用户控件，Loaded事件永远不会触发。为什么会这样？我怎样才能让它着火？

布局定义为：

<UserControl
    x:Class="MyProject.WP81.GenericPopup"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:local="using:MyProject.WP81"
    xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
    xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
    mc:Ignorable="d"
    d:DesignHeight="300"
    d:DesignWidth="400" Margin="0,1,0,-1"
    Loaded="GenericPopup_Loaded">
    <Popup Name="hostPopup">
        <Grid Name="contentGrid" VerticalAlignment="Center">
            <Grid.RowDefinitions>
                <RowDefinition x:Name="statusBarRow" Height="0" />
            </Grid.RowDefinitions>
            <ItemsControl Name="itemsControl" VerticalAlignment="Center" HorizontalAlignment="Center" />
            <Border Grid.Row="2" Background="#7F000000" />
        </Grid>
    </Popup>
</UserControl>

逻辑定义为：

namespace MyProject.WP81
{
    public sealed partial class GenericPopup : UserControl
    {
        public static bool IsOpen { get; private set; }
        public static GenericPopup Current { get; private set; }
        private UserControl _content;
        public GenericPopup(UserControl content)
        {
            Trace.trace("GenericPopup::Ctor()");
            _content = content;
            this.InitializeComponent();
            Initialise();
            SetContent(content);
        }
        private void Initialise()
        {
            Trace.trace("GenericPopup::Initialise()");
            RowDefinition rd = new RowDefinition();
            rd.MinHeight = Window.Current.Bounds.Height;
            rd.Height = new GridLength(Window.Current.Bounds.Height);
            contentGrid.RowDefinitions.Add(rd);
            contentGrid.Height = Window.Current.Bounds.Height;
            contentGrid.Width = Window.Current.Bounds.Width;
            contentGrid.Background = new SolidColorBrush(Colors.Black);
            contentGrid.Background.Opacity = 0.7;
            statusBarRow.MinHeight = Window.Current.Bounds.Height;
            statusBarRow.Height = new GridLength(Window.Current.Bounds.Height);
            Unloaded += (s, e) =>
            {
                Trace.trace("GenericPopup::Unloaded()");
                HardwareButtons.BackPressed -= HardwareButtons_BackPressed;
            };
            Trace.trace("GenericPopup::Initialised()");
        }
        private void GenericPopup_Loaded(object sender, RoutedEventArgs e)
        {
            Trace.trace("GenericPopup::GenericPopup_Loaded()");
            HardwareButtons.BackPressed += HardwareButtons_BackPressed;
            _content.Width = Window.Current.Bounds.Width;
        }
        public void SetContent(UserControl content)
        {
            Trace.trace("GenericPopup::SetContent()");
            _content = content;
            _content.Width = Window.Current.Bounds.Width;
            itemsControl.Items.Add(_content);
        }

        public async void Show()
        {
            Trace.trace("GenericPopup::Show()");
            this.Height = Window.Current.Bounds.Height;
            this.Width = Window.Current.Bounds.Width;
            hostPopup.IsOpen = true;
            IsOpen = hostPopup.IsOpen;
            Current = this;
        }
        public static void HideCurrent()
        {
            if (Current != null)
            {
                Current.Hide();
            }
        }
        internal void Hide()
        {
            //WinterfellToast.Show("msg popup:", "hide");
            hostPopup.IsOpen = false;
            IsOpen = hostPopup.IsOpen;
            Current = null;
        }
        void HardwareButtons_BackPressed(object sender, BackPressedEventArgs e)
        {
            Trace.trace("GenericPopup::HardwareButtons_BackPressed()");
            e.Handled = true;
            if (hostPopup.IsOpen)
            {
                hostPopup.IsOpen = false;                
            }
        }
    }
}

我按如下方式创建用户控件：

        var popopContent = new PopupContentUserControl(); 
        // any UserControl can be passed in as the content of the popup.
        // better if it's small though.
        _genericPopup = new GenericPopup(popopContent);
        _genericPopup.Show();    

我可以在跟踪中看到以下内容：

> 13:00:53.777  GenericPopup::Show() 
> 13:00:53.763  GenericPopup::SetContent() 
> 13:00:53.763  GenericPopup::Initialised() 
> 13:00:53.747  GenericPopup::Initialise() 
> 13:00:53.730  GenericPopup::Ctor()

因此，我们可以看到加载的事件不会触发。