Caliburn Micro：如何在 Windows Phone silverlight 中导航

Question

我正在尝试在我的 Windows Phone 7 项目中使用 Caliburn Micro。 但我在导航页面时遇到了 nullreferenceException。

namespace Caliburn.Micro.HelloWP7 {
    public class MainPageViewModel {
        readonly INavigationService navigationService;

        public MainPageViewModel(INavigationService navigationService) {
            this.navigationService = navigationService;
        }

        public void GotoPageTwo() {
            /*navigationService.UriFor<PivotPageViewModel>()
                .WithParam(x => x.NumberOfTabs, 5)
                .Navigate();*/
            navigationService.UriFor<Page1ViewModel>().Navigate();
        }
    }
}

namespace Caliburn.Micro.HelloWP7
{
    public class Page1ViewModel
    {
         readonly INavigationService navigationService;

         public Page1ViewModel(INavigationService navigationService)
         {
            this.navigationService = navigationService;
        }
    }
}

谁能告诉我我的代码有什么问题吗？提前致谢。

这是引导程序：

public class ScheduleBootstrapper : PhoneBootstrapper
{
    PhoneContainer container;

    protected override void Configure()
    {
        container = new PhoneContainer(RootFrame);

        container.RegisterPhoneServices();
        container.PerRequest<MainPageViewModel>();
        container.PerRequest<MainContentViewModel>();
        container.PerRequest<Page1ViewModel>();
        AddCustomConventions();
    }

    static void AddCustomConventions()
    {
        ConventionManager.AddElementConvention<Pivot>(Pivot.ItemsSourceProperty, "SelectedItem", "SelectionChanged").ApplyBinding =
            (viewModelType, path, property, element, convention) =>
            {
                if (ConventionManager
                    .GetElementConvention(typeof(ItemsControl))
                    .ApplyBinding(viewModelType, path, property, element, convention))
                {
                    ConventionManager
                        .ConfigureSelectedItem(element, Pivot.SelectedItemProperty, viewModelType, path);
                    ConventionManager
                        .ApplyHeaderTemplate(element, Pivot.HeaderTemplateProperty, viewModelType);
                    return true;
                }

                return false;
            };

        ConventionManager.AddElementConvention<Panorama>(Panorama.ItemsSourceProperty, "SelectedItem", "SelectionChanged").ApplyBinding =
            (viewModelType, path, property, element, convention) =>
            {
                if (ConventionManager
                    .GetElementConvention(typeof(ItemsControl))
                    .ApplyBinding(viewModelType, path, property, element, convention))
                {
                    ConventionManager
                        .ConfigureSelectedItem(element, Panorama.SelectedItemProperty, viewModelType, path);
                    ConventionManager
                        .ApplyHeaderTemplate(element, Panorama.HeaderTemplateProperty, viewModelType);
                    return true;
                }

                return false;
            };
    }

    protected override object GetInstance(Type service, string key)
    {
        return container.GetInstance(service, key);
    }

    protected override IEnumerable<object> GetAllInstances(Type service)
    {
        return container.GetAllInstances(service);
    }

    protected override void BuildUp(object instance)
    {
        container.BuildUp(instance);
    }
}

Answer 1

我也遇到了这个问题，并进行了如下跟踪：

如您所知，Caliburn.Micro 使用约定优于配置来定位 ViewModel 的视图，反之亦然，这意味着我们需要遵循约定。我的错误是 View 和 ViewModel 的 namespace 不一致。

在我的例子中，我有

MyWP7App.DetailsViewModel 和

MyWP7App.Views.DetailsView代码>

-->我将虚拟机的命名空间重命名为 MyWP7App.ViewModels.DetailsViewModel，效果很好。我认为我也可以将视图移动到 MyWP7App.DetailsView 中以获得良好的结果...

---

在幕后

调用 Navigate() 调用 DeterminePageName() ，而后者又调用 ViewLocator.LocateTypeForModelType

这与 CM 的其余部分一样是可重写的，但默认实现如下所示：

public static Func<Type, DependencyObject, object, Type> LocateTypeForModelType = (modelType, displayLocation, context) => {
    var viewTypeName = modelType.FullName.Substring(
        0,
        modelType.FullName.IndexOf("`") < 0
            ? modelType.FullName.Length
            : modelType.FullName.IndexOf("`")
        );

    Func<string, string> getReplaceString;
    if (context == null) {
        getReplaceString = r => { return r; };
    }
    else {
        getReplaceString = r => {
            return Regex.Replace(r, Regex.IsMatch(r, "Page$") ? "Page$" : "View$", ContextSeparator + context);
        };
    }

    var viewTypeList = NameTransformer.Transform(viewTypeName, getReplaceString);
    var viewType = (from assembly in AssemblySource.Instance
                    from type in assembly.GetExportedTypes()
                    where viewTypeList.Contains(type.FullName)
                    select type).FirstOrDefault();

    return viewType;
};

如果您遵循通过调试器，您最终会得到一个包含 MyWP7App.DetailsView 的集合 viewTypeList，以及一个全名为 MyWP7App.Views.DetailsView 的类型，因此返回的 viewType 为 null...这就是 NullReferenceException 的原因。

我 99% 确信 NameTransformer.Transform 调用将执行模式匹配，并将虚拟机命名空间中的 ViewModels 转换为 Views在它试图定位的视图的命名空间中...