IEventAggregator Prism 激活错误

Question

我在 WPF 中使用 Prism。当我将 IEventAggregator 作为参数添加到 ViewModel 构造函数时，出现此错误：'Microsoft.Practices.ServiceLocation.ActivationException' 类型的异常发生在 Microsoft.Practices.ServiceLocation.dll 中。附加信息：尝试获取对象类型的实例时发生激活错误，密钥 "CategoriesView"

这一行触发了异常：

private void NavigateToCategoriesRadioButton_Click(object sender, RoutedEventArgs e)
{
    this.regionManager.RequestNavigate(RegionNames.ConfigurationContentRegion, categoriesViewUri);
}

其中 categoriesViewUri 是：

private static Uri categoriesViewUri = new Uri("/CategoriesView", UriKind.Relative);

这是我的视图模型class:

[Export]
public class CategoriesViewModel : BindableBase
{
    private readonly IRegionManager regionManager;
    private readonly IEventAggregator eventAggregator;
    private readonly IConfigurationCategoriesService categoriesService;
    private readonly ObservableCollection<Category> categoriesCollection;
    private readonly ICollectionView categoriesView;
    private readonly DelegateCommand<object> deleteCategoryCommand;

    [ImportingConstructor]
    public CategoriesViewModel(IEventAggregator eventAggregator, IConfigurationCategoriesService categoriesService, IRegionManager regionManager)
    {    
        this.categoriesService = categoriesService;
        this.regionManager = regionManager;
        this.eventAggregator = eventAggregator;

        this.deleteCategoryCommand = new DelegateCommand<object>(this.DeleteCategory, this.CanDeleteCategory);

        this.categoriesCollection = new ObservableCollection<Category>(categoriesService.GetCategories());
        this.categoriesView = new ListCollectionView(this.categoriesCollection);
        this.categoriesView.CurrentChanged += (s, e) => this.deleteCategoryCommand.RaiseCanExecuteChanged();

    }

    public ICollectionView Categories
    {
        get { return this.categoriesView; } 
    }

    public ICommand DeleteCategoryCommand
    {
        get { return this.deleteCategoryCommand; }
    }

    private void DeleteCategory(object ignored)
    {
        var category = this.categoriesView.CurrentItem as Category;
        if (category != null)
        {
            categoriesService.DeleteCategory(category);
        }
    }
    private bool CanDeleteCategory(object ignored)
    {
        return true;
    }
}

看起来 CatagoriesViewModel 无法在构造函数上获取 IEventAggregator 的实例，但这是由 Prism 自动完成的，不是吗？在我从 Prism 文档 (StockTraderRI_Desktop) 获得的示例中，我没有看到实例化 EventAggregator 的任何地方。任何人都可以看到我做错了什么吗？提前致谢

已编辑：

Navitagion 项目视图已在 CategoriesModule 中注册 class:

[ModuleExport(typeof(CategoriesModule))]
public class CategoriesModule : IModule
{
    [Import]
    public IRegionManager regionManager;

    public void Initialize()
    {
        this.regionManager.RegisterViewWithRegion(RegionNames.ConfigurationNavigationRegion, typeof(CategoriesNavigationItemView));
    }
}

而 CategoriesView 代码隐藏是：

[Export("CategoriesView")]
public partial class CategoriesView : UserControl
{
    public CategoriesView()
    {
        InitializeComponent();
    }

    [Import]
    public IRegionManager regionManager;

    [Import]
    public CategoriesViewModel ViewModel
    {
        get { return this.DataContext as CategoriesViewModel; }
        set { this.DataContext = value; }
    }
}

Answer 1

我通过添加以下 using 语句解决了这个问题：

using Microsoft.Practices.Prism.PubSubEvents;

而不是

using Prism.Events;

我也根据本网站的推荐切换到 Unity 而不是 MEF。

IEventAggregator Prism 激活错误

Activation error with IEventAggregator Prism

c#

wpf

prism

eventaggregator