使用反射在运行时获取ConditionalAttribute的值

Question

I am working on a library that involves retrieving the methods of a given type. I have been using Type.GetMethods , but I've noticed an issue. Let's say that a method in the given type uses a ConditionalAttribute , and the value for this condition is false. GetMethods will still include this method, but I would like to ignore it.

Here is a simple example of what I am attempting. This program is ran in Debug mode, so I want to find a way where only foo() and fooDebug() are called while fooBar() is ignored.

using System;
using System.Diagnostics;
using System.Reflection;

namespace ConsoleApplication
{
    class ClassA
    {
        public static void foo()
        {
            Console.WriteLine("foo");
        }

        [Conditional("DEBUG")]
        public static void fooDebug()
        {
            Console.WriteLine("fooDebug");
        }

        [Conditional("BAR")]
        public static void fooBar()
        {
            Console.WriteLine("fooBar");
        }
    }

    class Program
    {
    //In this example, I want to find a way where only foo() and fooDebug() are called and fooBar() is ignored, when reflected.
        static void Main(string[] args)
        {
            //Call methods directly.
            //Methods are called/ignored as expected.
            ClassA.foo();//not ignored
            ClassA.fooDebug();//not ignored
            ClassA.fooBar();//ignored

            //Call methods with reflection
            MethodInfo[] methods = typeof(ClassA).GetMethods(BindingFlags.Static | BindingFlags.Public);
            foreach (MethodInfo method in methods)
            {
                //All methods are called, regardless of the ConditionalAttribute.
                method.Invoke(null, null);

                //I figured there would be some workaround like this:
                ConditionalAttribute conditional = 
                Attribute.GetCustomAttribute(method, typeof(ConditionalAttribute)) as ConditionalAttribute;

                if (conditional == null)
                {
                    //The method calls if it has no ConditionalAttribute
                    method.Invoke(null, null);
                }
                else
                {
                    //I can get the string of the condition; but I have no idea how, at runtime, to check if it's defined.
                    string conditionString = conditional.ConditionString;

                    //I also cannnot do a hardcoded (conditionString == "BAR") because the library would not know about BAR
                    bool conditionIsTrue = true;
                    //conditionIsTrue = ??

                    //If the method has a ConditionalAttribute, only call it if the condition is true
                    if (conditionIsTrue)
                    {
                        method.Invoke(null, null);
                    }
                }
            }
        }
    }
}

Ultimately, I would like to know which methods do not include false ConditionalAttributes.

EDIT

This idea is for a library that others would use, so assume that ClassA is a type that they define and pass into my library.

Answer 1

What this basically boils down to is: "can I determine, via reflection, the arbitrary conditional compilation symbols that were used to compile a given piece of code" - AFAIK, the answer to that is "no".

---

Note: everything under here no longer applies since the edit that makes it clear that the context here is library / caller.

If you have the luxury of being able to move the methods around (and make them non-public), then maybe:

partial class Program
{
    static partial void foo();
    static partial void fooDebug();
    static partial void fooBar();

    static partial void foo()
    {
        Console.WriteLine("foo");
    }

#if DEBUG
    static partial void fooDebug()
    {
        Console.WriteLine("fooDebug");
    }
#endif
#if BAR
    static partial void fooBar()
    {
        Console.WriteLine("fooBar");
    }
#endif
    //In this example, I want to find a way where only foo() and fooDebug() are called and fooBar() is ignored, when reflected.
    static void Main(string[] args)
    {
        //Call methods directly.
        //Methods are called/ignored as expected.
        foo();//not ignored
        fooDebug();//not ignored
        fooBar();//ignored

Now, the methods that aren't implemented do not exist after compile, so will not show in the reflection code. Note that you'd need use BindingFlags.Static | BindingFlags.NonPublic BindingFlags.Static | BindingFlags.NonPublic to find them now, since they are non-public:

MethodInfo[] methods = typeof(Program).GetMethods(BindingFlags.Static | BindingFlags.NonPublic);
foreach (MethodInfo method in methods)
{
    if(method.Name == "Main") continue; // yes, that is lazy
    method.Invoke(null, null);
}