Question

我尝试使用MEF完成一些事情，但现在，我遇到了一个需要帮助的问题。

描述：我有2个DLL和一个EXE文件。 ClassLibrary1（LoggerImpl.cs，SomeClass.cs） ClassLibrary2（ILogger.cs） WindowsApplicationForms1（WindowsApplicaitonForms1.cs，Program.cs）

我需要任何帮助或方向，为什么这不起作用？

// ClassLibrary1.dll
//SomeClass.cs
 public class SomeClass
    {
        [Import("Logging", typeof(ILogger))]
        public ILogger Log { get; set; } <-- ALWAYS NULL ???

        public void Print()
        {
            Log.Print();
        }

    }

// ClassLibrary1.dll
// LoggerImpl.cs
namespace ClassLibrary1
{
    [Export("Logging", typeof (ILogger))]
    public class LoggerImpl : ILogger
    {
        public void Print()
        {
            Console.WriteLine("print called");
        }
    }
}

// ClassLibrary2.dll
// ILogger.cs
namespace LogNamespace
{
    public interface ILogger
    {
        void Print();
    }
}

// WindowsFormsApplication1.exe
// WindowsFormsApplication1.cs
namespace WindowsFormsApplication1
{
    [Export("Form1",typeof(Form1))]
    public partial class Form1 : Form
    {

        [Import("Logging", typeof(ILogger))]
        public ILogger Log { set; get; }

        private CompositionContainer _container;

        public Form1()
        {
            InitializeComponent();
            Compose();
            Log.Print();

            SomeClass c = new SomeClass();
            c.Print();
        }

        private void Compose()
        {
            var catalog = new AggregateCatalog();

            catalog.Catalogs.Add(new DirectoryCatalog("."));
            catalog.Catalogs.Add(new AssemblyCatalog(System.Reflection.Assembly.GetExecutingAssembly()));
            _container = new CompositionContainer(catalog);

            try
            {
                _container.ComposeParts(this);
            }
            catch (CompositionException compositionException)
            {
                MessageBox.Show(compositionException.ToString());
            }
        }
    }
}

Answer 1

如果你自己创建一个新的类实例（new SomeClass（）），容器将不会知道它的任何内容，也不会组成它。

对于由MEF组成的部件，它需要由MEF创建，或者显式传递给容器。你可以手动告诉MEF满足SomeClass对象的导入，就像你告诉它满足表单的导入一样：

SomeClass c = new SomeClass();
_container.SatisfyImports(c);
c.Print();

但是，您需要直接访问容器来执行此操作，因此它在Form1类之外不能正常工作。通常，更好的方法是导出SomeClass，并在Form1类中为SomeClass创建一个导入：

[Export]
public class SomeClass
{
    [Import("Logging", typeof(ILogger))]
    public ILogger Log { get; set; }

    // etc.
}

public partial class Form1 : Form
{
    [Import("Logging", typeof(ILogger))]
    public ILogger Log { set; get; }

    [Import]
    SomeClass _someClass { get; set; }

    // etc.
}

Answer 2

您需要一个类似于以下内容的声明，以便在合成过程中使用SomeClass

// ClassLibrary1.dll
//SomeClass.cs
using System;
using System.ComponentModel.Composition;
using System.ComponentModel.Composition.Hosting;
using System.Windows.Forms;
using LogNamespace;

public class SomeClass
{
    [Import("Logging", typeof(ILogger))]
    public ILogger Log { get; set; } //<-- ALWAYS NULL ???

    public SomeClass()
    {
        var catalog = new AggregateCatalog();
        CompositionContainer _container;

        // catalog.Catalogs.Add(new DirectoryCatalog("."));
        catalog.Catalogs.Add(new AssemblyCatalog(System.Reflection.Assembly.GetExecutingAssembly()));
        _container = new CompositionContainer(catalog);

        _container.ComposeParts(this);
    }

    public void Print()
    {
        Log.Print();
    }

}

// ClassLibrary1.dll
// LoggerImpl.cs
namespace ClassLibrary1
{
    [Export("Logging", typeof(ILogger))]
    public class LoggerImpl : ILogger
    {
        public void Print()
        {
            Console.WriteLine("print called");
        }
    }
}

// ClassLibrary2.dll
// ILogger.cs
namespace LogNamespace
{
    public interface ILogger
    {
        void Print();
    }
}

// WindowsFormsApplication1.exe
// WindowsFormsApplication1.cs
namespace WindowsFormsApplication1
{
    [Export("Form1", typeof(Form1))]
    public partial class Form1 : Form
    {

        [Import("Logging", typeof(ILogger))]
        public ILogger Log { set; get; }

        private CompositionContainer _container;

        public Form1()
        {
            InitializeComponent();
            Compose();
            Log.Print();

            SomeClass c = new SomeClass();
            c.Print();
        }

        private void Compose()
        {
            var catalog = new AggregateCatalog();

            // catalog.Catalogs.Add(new DirectoryCatalog("."));
            catalog.Catalogs.Add(new AssemblyCatalog(System.Reflection.Assembly.GetExecutingAssembly()));
            _container = new CompositionContainer(catalog);

            try
            {
                _container.ComposeParts(this);
            }
            catch (CompositionException compositionException)
            {
                MessageBox.Show(compositionException.ToString());
            }
        }
    }
}

导入属性始终为null（MEF导入问题）

2 个答案: