c# - MEF 在导入程序集的构造函数中导入程序集不起作用 - 通过调用方法导入是否有效？

Question

我很好奇为什么会发生以下情况:

当我在导入的程序集中使用 ImportMany 并在导入的程序集的构造函数中调用 compose 方法时，我可以看到 ImportMany IEnumerable 已被填充但是一旦我走出构造函数并返回父程序集的代码，移动鼠标光标悬停在刚刚导入的程序集上，它的 ImportMany IENumerable 是空的!

如果我在从“父”程序集调用的方法中进行组合，一切正常。

意味着以下内容不起作用:示例代码(父级):

    private CompositionContainer modules;
    private AggregateCatalog catalogOfModules = new AggregateCatalog();
    #region MEF Imports
    [Import(typeof(IMyTypedInterface<someOtherInterface>),AllowDefault=true)]
    public someOtherInterface someObject;
    public void StartProgram()
    {
        try
        {
            catalogOfModules.Catalogs.Add(new DirectoryCatalog(System.IO.Path.GetDirectoryName(System.Reflection.Assembly.GetExecutingAssembly().Location) + System.IO.Path.DirectorySeparatorChar + "directoryWichContainsMyAssembly"));
            modules = new CompositionContainer(catalogOfModules);
            modules.ComposeParts(this); 
            someObject.listOfModules.Count; # is 0              
        }
        catch (CompositionException)
        {
        }
    }

示例代码(子):

[Export(typeof(IMyTypedInterface<someOtherInterface>))]
public class ExampleChild{
    [ImportMany(typeof(someInterface))]
    private IEnumerable<someInterface> listOfModules;
    private CompositionContainer modules;
    private AggregateCatalog catalogOfModules = new AggregateCatalog();
    public ExampleChild()
    {
        catalogOfModules.Catalogs.Add(new DirectoryCatalog(System.IO.Path.GetDirectoryName(System.Reflection.Assembly.GetExecutingAssembly().Location) + System.IO.Path.DirectorySeparatorChar + "someDirectoryWithAssemblies"));
        modules = new CompositionContainer(catalogOfModules);
        modules.ComposeParts(this);
        listOfModules.Count; # is 2
    }
}

===========================================

但这确实有效

示例代码(父级):

    private CompositionContainer modules;
    private AggregateCatalog catalogOfModules = new AggregateCatalog();
    #region MEF Imports
    [Import(typeof(IMyTypedInterface<someOtherInterface>),AllowDefault=true)]
    public someOtherInterface someObject;
    public void StartProgram()
    {
        try
        {
            catalogOfModules.Catalogs.Add(new DirectoryCatalog(System.IO.Path.GetDirectoryName(System.Reflection.Assembly.GetExecutingAssembly().Location) + System.IO.Path.DirectorySeparatorChar + "directoryWichContainsMyAssembly"));
            modules = new CompositionContainer(catalogOfModules);
            modules.ComposeParts(this);     
            if (someObject != null)
            {
                someObject.ComposeMethod();
                someObject.listOfModules.Count; # is 2
            }
        }
        catch (CompositionException)
        {
        }
    }

示例代码(子):

[Export(typeof(IMyTypedInterface<someOtherInterface>))]
public class ExampleChild : IMyTypedInterface<someOtherInterface>, someOtherInterface{
    [ImportMany(typeof(someInterface))]
    private IEnumerable<someInterface> listOfModules;
    private CompositionContainer modules;
    private AggregateCatalog catalogOfModules = new AggregateCatalog();
    public void ComposeMethod()
    {
        catalogOfModules.Catalogs.Add(new DirectoryCatalog(System.IO.Path.GetDirectoryName(System.Reflection.Assembly.GetExecutingAssembly().Location) + System.IO.Path.DirectorySeparatorChar + "CM"));
        modules = new CompositionContainer(catalogOfModules);
        modules.ComposeParts(this);
        listOfModules.Count; # is 2
    }
}

有人可以向我解释这种行为的原因吗？

Answer 1

我的错误是在每个具有子模块的模块中调用“modules.ComposeParts”。相反，只需调用“核心”中的 ComposePart。其他一切都由 MEF 处理。于是 child 的代码就变成了这样:

[Export(typeof(IMyTypedInterface<someOtherInterface>))]
public class ExampleChild : IMyTypedInterface<someOtherInterface>, someOtherInterface
{
    [ImportMany(typeof(someInterface))]
    private IEnumerable<someInterface> listOfModules;        
}