在Caliburn.Micro中使用PCL MEF2

Question

为了使用MEF2的PCL版本，我不确定如何连接Caliburn.Micro。我见过MefBootstrapper example，但它使用了许多不可用的类，我在转换到新的API时遇到了麻烦。

这是我到目前为止所知道的：

using System;
using System.Collections.Generic;
using System.Composition;
using System.Composition.Hosting;
using System.Linq;
using Caliburn.Micro;

namespace Test
{
    public class Bootstrapper : BootstrapperBase
    {
        private CompositionHost _host;

        public Bootstrapper()
        {
            Initialize();
        }

        protected override void Configure()
        {
            var config = new ContainerConfiguration();
            config.WithAssemblies(AssemblySource.Instance);

//            batch.AddExportedValue<IWindowManager>(new WindowManager());
//            batch.AddExportedValue<IEventAggregator>(new EventAggregator());
//            batch.AddExportedValue(container);

            _host = config.CreateContainer();
        }

        protected override object GetInstance(Type serviceType, string key)
        {
            string contract = string.IsNullOrEmpty(key) ? serviceType.ToString() : key;
            var exports = _host.GetExports<object>(contract).ToArray();

            if (exports.Any())
                return exports.First();

            throw new Exception(string.Format("Could not locate any instances of contract {0}.", contract));
        }

        protected override IEnumerable<object> GetAllInstances(Type serviceType)
        {
            return _host.GetExports<object>(serviceType.ToString());
        }

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

        protected override void OnStartup(object sender, System.Windows.StartupEventArgs e)
        {
            DisplayRootViewFor<IShell>();
        }
    }
}

但是，CompositionHost似乎没有任何导出，我也不知道如何向其中添加对象(WindowManager和EventAggregator)。

Answer 1

在尝试了一下之后，下面是我想出的方法，它似乎起作用了：

[Export(typeof(IWindowManager))]
public class MyWindowManager : WindowManager
{
}

[Export(typeof(IEventAggregator))]
public class MyEventAggregator : EventAggregator
{
}

public interface IShell
{
}

public class AppBootstrapper : BootstrapperBase
{
    private CompositionHost _host;

    public AppBootstrapper()
    {
        Initialize();
    }

    protected override IEnumerable<Assembly> SelectAssemblies()
    {
        // TODO: Add additional assemblies here
        yield return typeof(AppBootstrapper).GetTypeInfo().Assembly;
    }

    protected override void Configure()
    {
        var config = new ContainerConfiguration();
        var assemblies = AssemblySource.Instance.Union(SelectAssemblies());
        config.WithAssemblies(assemblies);

        _host = config.CreateContainer();
    }

    protected override object GetInstance(Type serviceType, string key)
    {
        var exports = _host.GetExports(serviceType, key).ToArray();

        if (exports.Any())
            return exports.First();

        throw new Exception(string.Format("Could not locate any instances of contract {0}.", serviceType.Name));
    }

    protected override IEnumerable<object> GetAllInstances(Type serviceType)
    {
        return _host.GetExports<object>(serviceType.ToString());
    }

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

    protected override void OnStartup(object sender, System.Windows.StartupEventArgs e)
    {
        DisplayRootViewFor<IShell>();
    }
}

Answer 2

我的回复肯定是晚了，但也许这对其他正在为可怜的MEF2文档而苦苦挣扎的人有帮助，当然它也可能对我有帮助，如果有人想出更好的实现，或者在这个解决方案中发现任何问题；所以就是这样。

对于面向属性较少的方法(这是基本的MEF2特性之一)，为了避免将CM注入包包装到自定义类中的麻烦，您必须配置程序集导出，如下所示：

protected override IEnumerable<Assembly> SelectAssemblies()
{
    return new[]
    {    
        typeof (IEventAggregator).GetTypeInfo().Assembly,
        typeof (IWindowManager).GetTypeInfo().Assembly,
        typeof (MefBootstrapper).GetTypeInfo().Assembly
    };
}    

protected override void Configure()
{
    var config = new ContainerConfiguration();

    // note that the event aggregator is in the core CM assembly,
    // while the window manager in the platform-dependent CM assembly,
    // so that we need 2 conventions for 2 assemblies.
    ConventionBuilder cmBuilder = new ConventionBuilder();
    cmBuilder.ForType<EventAggregator>().Export<IEventAggregator>();

    ConventionBuilder cmpBuilder = new ConventionBuilder();
    cmpBuilder.ForType<WindowManager>().Export<IWindowManager>();

    ConventionBuilder appBuilder = new ConventionBuilder();
    appBuilder.ForTypesMatching(t =>
        t.Name.EndsWith("ViewModel", StringComparison.OrdinalIgnoreCase)).Export();
    appBuilder.ForType<MainViewModel>().Export<IShell>();

    config.WithAssembly(typeof(IEventAggregator).GetTypeInfo().Assembly, cmBuilder);
    config.WithAssembly(typeof(IWindowManager).GetTypeInfo().Assembly, cmpBuilder);
    config.WithAssembly(typeof(MefBootstrapper).GetTypeInfo().Assembly, appBuilder);

    _host = config.CreateContainer();
}

从本质上讲，你必须注意几件事：

1. CM对象分布在不同的程序集中，因为一些对象在所有平台之间共享，而其他对象则更特定于平台。在这种情况下，事件聚合器在CM核心程序集中，而窗口管理器在Caliburn.Micro.Platform中。
2. 在MEF2中，您可以使用约定自动标记为导出所需的对象。在我的示例中，我将EventAggregator标记为exports，作为要为接口IEventAggregator选择的实现，对于窗口管理器也是如此；此外，我将主视图模型作为IShell接口的实现导出，并通过从我的应用程序集中导出名称以ViewModel结尾的所有类来导出所有视图模型。这样，我就不需要任何ExportAttribute.

了