.net - 为什么我不能用 Ninjects ConstructorArgument 注入(inject) null 值？

Question

使用 Ninjects ConstructorArgument 时，您可以指定要注入(inject)特定参数的确切值。为什么这个值不能为空，或者我怎样才能让它工作？也许这不是您想做的事情，但我想在我的单元测试中使用它。示例:

public class Ninja
{
    private readonly IWeapon _weapon;
    public Ninja(IWeapon weapon)
    {
        _weapon = weapon;
    }
}

public void SomeFunction()
{
    var kernel = new StandardKernel();
    var ninja = kernel.Get<Ninja>(new ConstructorArgument("weapon", null));
}

Answer 1

查看源代码(以及我通过复制获得的堆栈跟踪，您省略了:P)

这是因为它绑定(bind)到 ConstructorArgument 的不同重载。 ctor 比正常用法(即，您传递值类型或非空引用类型的地方)所做的。

解决方法是将 null 转换为 Object:-

var ninja = kernel.Get<Ninja>( new ConstructorArgument( "weapon", (object)null ) );

忍者 2 来源:

public class ConstructorArgument : Parameter
{
    /// <summary>
    /// Initializes a new instance of the <see cref="ConstructorArgument"/> class.
    /// </summary>
    /// <param name="name">The name of the argument to override.</param>
    /// <param name="value">The value to inject into the property.</param>
    public ConstructorArgument(string name, object value) : base(name, value, false) { }

    /// <summary>
    /// Initializes a new instance of the <see cref="ConstructorArgument"/> class.
    /// </summary>
    /// <param name="name">The name of the argument to override.</param>
    /// <param name="valueCallback">The callback to invoke to get the value that should be injected.</param>
    public ConstructorArgument(string name, Func<IContext, object> valueCallback) : base(name, valueCallback, false) { }
}

复制:

public class ReproAndResolution
{
    public interface IWeapon
    {
    }

    public class Ninja
    {
        private readonly IWeapon _weapon;
        public Ninja( IWeapon weapon )
        {
            _weapon = weapon;
        }
    }

    [Fact]
    public void TestMethod()
    {
        var kernel = new StandardKernel();
        var ninja = kernel.Get<Ninja>( new ConstructorArgument( "weapon", (object)null ) );
    }
}

课？如果您不下载最新的源代码并查看它，您会发疯的。很棒的评论，干净的代码库。再次感谢@Ian Davis 的提示/刺激!