C# Conditional Attribute Testing

Code

using System;
using System.Diagnostics;

namespace TestingConditionalAttribute
{
    /// <summary>
    /// Testing Conditional Attribute
    /// author  :   Jave.Lin
    /// date    :   2018-06-08
    /// </summary>
    class Program
    {
        static void Main(string[] args)
        {
#if DEBUG
            WL("Had Defined 'DEBUG' compile symbol");
#endif
#if !RELEASE
            WL("Have No Defined 'RELEASE' compile symbol", ConsoleColor.Yellow);
#endif
            TestCls.TestDebugMethod("This is [Debug] Message.");
            TestCls.TestReleaseMethod("This is [Release] Message."); // cann't output, due to Conditional("RELEASE")
            var methodInfo = typeof(TestCls).GetMethod("TestDebugMethod");
            WL($"GetMethod(\"TestDebugMethod\"): {methodInfo?.Name}");
            methodInfo = typeof(TestCls).GetMethod("TestReleaseMethod");
            WL($"GetMethod(\"TestReleaseMethod\"): {methodInfo?.Name}");
            methodInfo.Invoke(null, new object[] { $"Reflection to call {methodInfo?.Name}, This is [Release] Message", ConsoleColor.Yellow });

            WL("Press any key to exit.");
            Console.Read();
        }

        public static void WL(string msg, ConsoleColor? color = null)
        {
            if (color.HasValue)
            {
                var srcColor = Console.ForegroundColor;
                Console.ForegroundColor = color.Value;
                Console.WriteLine(msg);
                Console.ForegroundColor = srcColor;
            }
            else
            {
                Console.WriteLine(msg);
            }
        }
    }

    class TestCls : Attribute
    {
        [Conditional("DEBUG")]
        public static void TestDebugMethod(string msg)
        {
            Program.WL($"TestDebugMethod msg : {msg}");
        }
        [Conditional("RELEASE")]
        public static void TestReleaseMethod(string msg, ConsoleColor? color = null)
        {
            Program.WL($"TestReleaseMethod msg : {msg}", color);
        }
    }
}

Running

Others Attribute

• Obsolete 一般用于警告、错误的方式编译提示：过期的API
• Conditional 上述示例，不再多讲，有点类似：#define xxx, #if xxx #endif的方式，但代码是编进去的，IL可以看到。
• AttributeUsage (DOCS) 是方便C#用户扩展自定义Attribute是定位该Attribute的特性：
  
  • 用于什么位置：类、方法、字段、参数、返回值、等等；
  • 能否让派生类有持有该Attribute，或是能否多Attribute都可以限定。