问题描述

我创建了一个简单的属性:

I've created a simple Attribute:

[AttributeUsage(AttributeTargets.Method)]
public class InitAttribute : System.Attribute
{
    public InitAttribute()
    {
        Console.WriteLine("Works!");
    }
}

我将其应用于一个简单的方法:

and I apply it to a simple method:

static class Logger
{
    public static string _severity;

    public static void Init(string severity)
    {
        _severity = severity;
    }

    [Init()]
    public static void p()
    {
        Console.WriteLine(_severity);
    }
}

正在发生的事情非常直接.只是，我希望该属性执行一个操作(打印 Works！)，但这不会发生.

What is going on is pretty streight-forward. Only, I expect the attribute to perform an action (printing Works!), but this does not happen.

另外，打印Works！"当然只是出于调试目的:我想访问 instance 的属性 _severity(例如，检查是否为 != null)，但我所做的一切继续阅读属性(对我来说很新)是关于通过反射访问类的方法或属性等等.一旦我评估了 _severity，我该如何修改被装饰方法的行为(在这种情况下，引发异常记录器未初始化"并且不执行它)?

Addictionally, printing "Works!" is of course just for debugging purposes: I'd like to access the instance's property _severity (to check if is != null, for example), but everything I keep reading about attributes (that are pretty new to me) is about accessing the class' methods or properties and so on via reflection. Once I've evaluated _severity, how can I modify the behavior of the decorated method (in this case, rise an exception "Logger is not initialized" and do not execute it)?

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推荐答案

如果您需要在控件进入方法时执行操作，您应该查看 面向方面的编程和框架，例如 PostSharp.属性并非旨在自行执行任何操作.它们只是附加在 IL 程序集中的东西上的一堆数据(或元数据，如果你愿意的话)，可以在运行时查询.

If you need to perform an action as control enters a method, you should look at aspect-oriented programming and frameworks such as PostSharp. Attributes are not designed to perform anything by themselves. They are just a bunch of data (or metadata if you will) attached to stuff in IL assemblies that can be queried at runtime.

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