WPF MVVM DataTemplates -视图未更新

我正在开发一个数字标牌WPF应用程序，基本结构设置如下:

我有一个视图，其中有一个网格绑定到一个播放列表对象。播放列表包含窗格，窗格包含播放列表项，每个播放列表项包含一个内容项。我使用DataTemplates为每个片段构建视图，例如

    <!-- This template represents a single content pane, no real display here, just empty space with a height and width -->
    <DataTemplate DataType="{x:Type entities:ContentPane}">
        <ContentControl 
            Content="{Binding CurrentPlaylistItem, Mode=OneWay}" 
            Height="{Binding Height, Mode=OneTime}" 
            Width="{Binding Width, Mode=OneTime}" 
            HorizontalAlignment="Left"
            VerticalAlignment="Top"                
            />
    </DataTemplate>
    <!-- This is a playlist item which is contained within a ContentPane.
         This also has no real display, just a placeholder for the content item, and will likely contain some transition information-->
    <DataTemplate DataType="{x:Type entities:PlaylistItem}">
        <inf:TransitionableContentControl Content="{Binding ContentItem}"></inf:TransitionableContentControl>
    </DataTemplate>

    <!-- image item template 
         the path can be any valid uri e.g. http://... or file://... -->
    <DataTemplate DataType="{x:Type contentTypes:ImageContentType}">
        <Grid Background="Transparent" x:Name="ImageType">
            <Image Source="{Binding Bitmap, Mode=OneTime}"></Image>
            <inf:BusinessAd
                        ContainerHeight="{Binding ImageHeight, Mode=OneTime}"
                        ContainerWidth="{Binding ImageWidth, Mode=OneTime}"                            
                        Visibility="{Binding AdText, Converter={StaticResource _VisibilityConverter}, Mode=OneWay}"
                        Text="{Binding AdText.Text, Mode=OneTime}"
                        AdFontSize="{Binding AdText.TextStyle.FontSize}"
                        AdFontFamily="{Binding AdText.TextStyle.FontFamily}">
                <ContentControl 
                    Content="{Binding AdText, Mode=OneTime}"                         
                    ContentTemplate="{StaticResource BusinessAdTextTemplate}">
                </ContentControl>
            </inf:BusinessAd>
        </Grid>
    </DataTemplate>

随着数据上下文的变化，每个窗格中的内容从一个项转换到下一个项。我遇到了一个问题，用户在一个窗格中连续放置两次相同的项目，无论是视频，图像等。发生的情况是，更改没有被检测到，UI也没有更新。在视频的情况下，它在第一个视频的最后一帧冻结，整个应用程序挂起。

我试过在PlaylistItem类中做一个OnPropertyChanged("ContentItem")，试着在我的数据模板上设置Shared="False"，我试着改变ContentItem对象的属性并引发PropertyChanged事件，似乎没有任何作用。我打开了对数据绑定的跟踪，看看发生了什么，一切似乎都工作正常。当我更改ContentItem的属性时，它会显示新项目的新散列，但UI上没有更改。

在PlaylistItem中的TransitionableContentControl中，当从一个内容项到同一个内容项时，OnContentChanged覆盖永远不会被击中。如果我把那个控件换成常规的ContentControl，没有变化

// CurrentPlaylistItem = pli ; -- not good
Application.Current.Dispatcher.Invoke (new Action (() =>
{
    // clear item
    // null doesn't work, because TransitionableContentControl's
    // inner ContentControl would be empty and the brush created 
    // from it would be a null brush (no visual effect)
    CurrentPlaylistItem = new PlaylistItem () ;
    this.OnPropertyChanged ("CurrentPlaylistItem") ;
    Application.Current.Dispatcher.Invoke (new Action (() =>
    {
        // set new item, possibly same as old item
        // but WPF will have forgotten that because
        // data bindings caused by the assignment above
        // have already been queued at the same DataBind 
        // level and will execute before this assignment
        CurrentPlaylistItem = pli ; 
        this.OnPropertyChanged ("CurrentPlaylistItem") ;
    }), DispatcherPriority.DataBind) ;
})) ;