Delegate.Create Delegate 示例

main.cs

using System.Diagnostics;
using System.Reflection;
using System.Runtime.CompilerServices;

namespace Playground;

internal static class Program
{
    private static void Main()
    {
        Processor.Process(12); // ==> Process int
        Processor.Process("string"); // ==> Process string
        Processor.Process(1.0); // ==> Process double
    }
}

[AttributeUsage(AttributeTargets.Method)]
internal class ProcessorAttribute : Attribute
{
    public readonly Type Type;

    public ProcessorAttribute(Type type)
    {
        Type = type;
    }
}

internal static class Processor
{
    public static Dictionary<Type, Action<object>> Dict { get; private set; } = null!;

    [ModuleInitializer]
    public static void Init()
    {
        Dict = typeof(Processor).GetMethods(BindingFlags.Static | BindingFlags.Public)
            .SelectMany(methodInfo =>
            {
                if (methodInfo.GetCustomAttribute<ProcessorAttribute>() is not { } attribute)
                    return Enumerable.Empty<(Type type, Action<object> action)>();
                var action = (Action<object>) Delegate.CreateDelegate(typeof(Action<object>), null, methodInfo);
                return new[] { (attribute.Type, action) };
            })
            .ToDictionary(tuple => tuple.type, tuple => tuple.action);
    }

    public static void Process(object o)
    {
        Dict[o.GetType()].Invoke(o);
    }

    [Processor(typeof(int))]
    public static void ProcessInt(object value)
    {
        Debug.Assert(value is int);
        Console.Out.WriteLine("Process int");
    }

    [Processor(typeof(double))]
    public static void ProcessDouble(object value)
    {
        Debug.Assert(value is double);
        Console.Out.WriteLine("Process double");
    }

    [Processor(typeof(string))]
    public static void ProcessString(object value)
    {
        Debug.Assert(value is string);
        Console.Out.WriteLine("Process string");
    }
}