具有多个构造函数的 MEF 构造函数参数

发布于 2024-09-03 21:56:57 字数 683 浏览 5 评论 0原文

我开始使用 MEF，并且我有一个具有多个构造函数的类，如下所示：

[Export(typeof(ifoo))]
class foo : ifoo {
    void foo() { ... }
    [ImportingConstructor]
    void foo(object par1) { ... }
}

我在编写时使用 catalog.ComposeExportedValue() 来提供 par1 第二个构造函数的值：

...
catalog.ComposeExportedValue(par1Value);
catalog.ComposeParts(this);
...

保存我正在使用的组件：

[ImportMany(typeof(ifoo))]
public List<Lazy<ifoo, ifoometadata>> FooList { get; set; }

并创建我使用 value 属性 FooList[0].Value 的 foo 实例。

一切正常，除了 foo 类的第二个构造函数从未被调用。怎么了？

MEF 实例化类时如何选择要使用的构造函数？

原文

I'm starting to use MEF, and I have a class with multiple constructors, like this:

[Export(typeof(ifoo))]
class foo : ifoo {
    void foo() { ... }
    [ImportingConstructor]
    void foo(object par1) { ... }
}

I am using catalog.ComposeExportedValue() when composing to supply the par1
value to second constructor:

...
catalog.ComposeExportedValue(par1Value);
catalog.ComposeParts(this);
...

To hold the components I'm using:

[ImportMany(typeof(ifoo))]
public List<Lazy<ifoo, ifoometadata>> FooList { get; set; }

And to create the foo instance I'm using the value property, FooList[0].Value.

Everthing works fine, except that the second constructor of the foo class is never called. What's wrong?

How do I select the constructor I want to use when MEF instantiates the class?

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凑诗 2024-09-10 21:56:58

您是否将 foo 类的实例传递到 ComposeExportedValue 方法中？在这种情况下，对象已经被构造并且不能再次调用构造函数，因此 MEF 将忽略构造函数导入。

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秋叶绚丽 2024-09-10 21:56:57

MEF 应使用您放置 ImportingConstructorAttribute 的构造函数。我不确定您发生了什么，我无法重现该问题。这是一个测试，显示在也具有默认构造函数的类上使用 ImportingConstructor：

[TestClass]
public class MefTest
{
    public const string ConstructorParameterContract = "FooConstructorParameterContract";

    [TestMethod]
    public void TestConstructorInjectionWithMultipleConstructors()
    {
        string ExpectedConstructorParameterValue = "42";

        var catalog = new TypeCatalog(typeof(Foo), typeof(FooImporter));
        var container = new CompositionContainer(catalog);

        container.ComposeExportedValue<string>(ConstructorParameterContract, ExpectedConstructorParameterValue);

        var fooImporter = container.GetExportedValue<FooImporter>();

        Assert.AreEqual(1, fooImporter.FooList.Count, "Expect a single IFoo import in the list");
        Assert.AreEqual(ExpectedConstructorParameterValue, fooImporter.FooList[0].Value.ConstructorParameter, "Expected foo's ConstructorParameter to have the correct value.");
    }
}

public interface IFoo
{
    string ConstructorParameter { get; }
}

[Export(typeof(IFoo))]
public class Foo : IFoo
{
    public Foo()
    {
        ConstructorParameter = null;
    }

    [ImportingConstructor]
    public Foo([Import(MefTest.ConstructorParameterContract)]string constructorParameter)
    {
        this.ConstructorParameter = constructorParameter;
    }


    public string ConstructorParameter { get; private set; }
}

[Export]
public class FooImporter
{
    [ImportMany]
    public List<Lazy<IFoo>> FooList { get; set; }
}

MEF should use the constructor you put the ImportingConstructorAttribute on. I'm not sure what is happening for you, I wasn't able to reproduce the issue. Here is a test which shows using an ImportingConstructor on a class that also has a default constructor:

[TestClass]
public class MefTest
{
    public const string ConstructorParameterContract = "FooConstructorParameterContract";

    [TestMethod]
    public void TestConstructorInjectionWithMultipleConstructors()
    {
        string ExpectedConstructorParameterValue = "42";

        var catalog = new TypeCatalog(typeof(Foo), typeof(FooImporter));
        var container = new CompositionContainer(catalog);

        container.ComposeExportedValue<string>(ConstructorParameterContract, ExpectedConstructorParameterValue);

        var fooImporter = container.GetExportedValue<FooImporter>();

        Assert.AreEqual(1, fooImporter.FooList.Count, "Expect a single IFoo import in the list");
        Assert.AreEqual(ExpectedConstructorParameterValue, fooImporter.FooList[0].Value.ConstructorParameter, "Expected foo's ConstructorParameter to have the correct value.");
    }
}

public interface IFoo
{
    string ConstructorParameter { get; }
}

[Export(typeof(IFoo))]
public class Foo : IFoo
{
    public Foo()
    {
        ConstructorParameter = null;
    }

    [ImportingConstructor]
    public Foo([Import(MefTest.ConstructorParameterContract)]string constructorParameter)
    {
        this.ConstructorParameter = constructorParameter;
    }


    public string ConstructorParameter { get; private set; }
}

[Export]
public class FooImporter
{
    [ImportMany]
    public List<Lazy<IFoo>> FooList { get; set; }
}

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