c# - 如何从 Action<T> 获取方法的自定义属性？

Question

如何从 Action<T> 中获取方法的自定义属性代表？

例子:

//simple custom attribute
public class StatusAttribute : Attribute
{

    public string Message { get; set; } = string.Empty;
}

// an extension methodto wrap MethodInfo.GetCustomAttributes(Type, Bool) with
// generics for the custom Attribute type
public static class MethodInfoExtentions
{
    public static IEnumerable<TAttribute> GetCustomAttributes<TAttribute>(this MethodInfo methodInfo, bool inherit) where TAttribute : Attribute
    {
        object[] attributeObjects = methodInfo.GetCustomAttributes(typeof(TAttribute), inherit);
        return attributeObjects.Cast<TAttribute>();
    }
}

// test class with a test method to implment the custom attribute
public class Foo
{
    [Status(Message="I'm doing something")]
    public void DoSomething()
    {
        // code would go here       
    }
}

// creates an action and attempts to get the attribute on the action
private void CallDoSomething()
{
    Action<Foo> myAction = new Action<Foo>(m => m.DoSomething());
    IEnumerable<StatusAttribute> statusAttributes = myAction.Method.GetCustomAttributes<StatusAttribute>(true);

    // Status Attributes count = 0? Why?
}

我意识到我可以通过在 Foo 上使用反射来做到这一点，但是对于我要创建的内容，我必须使用 Action<T> .

Answer 1

问题是这个 Action 没有直接指向Foo.DoSomething .它指向编译器生成的以下形式的方法:

private static void <>__a(Foo m)
{
    m.DoSomething();
}

此处的一个选项是将其更改为 Expression<Action<T>> ，然后您可以在之后剖析表达式树并提取属性:

Expression<Action<Foo>> myAction = m => m.DoSomething();
var method = ((MethodCallExpression)myAction.Body).Method;
var statusAttributes = method.GetCustomAttributes<StatusAttribute>(true);
int count = statusAttributes.Count(); // = 1