app.xaml中的StaticResource在app.xaml引用的资源字典中找不到

Question

我有一种情况，我试图解析资源字典中引用的数据模板中的可视化组件，引用app.xaml标记的静态资源，请参阅下面的示例。

/App.xaml

<Application 
    x:Class="App" 
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation" 
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"      
    xmlns:composition="clr-namespace:Composition"
    ShutdownMode="OnMainWindowClose">
    <Application.Resources>
        <ResourceDictionary>
            <composition:ApplicationContainer x:Key="ApplicationContainer"/>
            <ResourceDictionary.MergedDictionaries>
                <ResourceDictionary Source="pack://application:,,,/MyApp;component/Composition/DataTemplates.xaml"/>
            </ResourceDictionary.MergedDictionaries>
        </ResourceDictionary>
    </Application.Resources>
</Application>

/Composition/DataTemplates.xaml

<ResourceDictionary xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
                    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
                    xmlns:projectvm="clr-namespace:ViewModels.ProjectManagement"
                    xmlns:unity="clr-namespace:Extensions">
    <DataTemplate DataType="{x:Type projectvm:ProjectDocument}">
        <ContentControl>
            <!-- Custom Extension that resolves a component from the composition container -->
            <unity:Resolve Container="{StaticResource ApplicationContainer}" TargetType="{x:Type projectvm:ProjectDocument}" ContractName="ProjectDocument"/>
        </ContentControl>
    </DataTemplate>
</ResourceDictionary> 

ERROR就在上面，统一：Resolve行找不到ApplicationContainer静态资源，我不明白为什么。