使用字符串作为类型的参数，当调用构造函数时

Question

我正在尝试基于字符串参数创建类型，并将其传递给构造函数的类型参数。仅使用if语句进行检查时，它会变得很讨厌，我不知道该如何通过编程/通用方式进行。

我尝试了反射，但是仅返回一个对象并将对象传递给显然不起作用。

没有人知道如何在没有成千上万的if语句的情况下以更巧妙的方式解决此问题吗？

对象创建看起来像这样：

                if (Options.Input1Type == "int" && Options.Output1Type == "int") return BlockBuilder.Build<int, int>(Kind, Options, TransformToSelf);
                if (Options.Input1Type == "bool" && Options.Output1Type == "bool") return BlockBuilder.Build<bool, bool>(Kind, Options, TransformToSelf);
                if (Options.Input1Type == "string" && Options.Output1Type == "string") return BlockBuilder.Build<string, string>(Kind, Options, TransformToSelf);

                if (Options.Input1Type == "bool" && Options.Output1Type == "int") return BlockBuilder.Build<bool, int>(Kind, Options, TransformToInt);
                if (Options.Input1Type == "bool" && Options.Output1Type == "string") return BlockBuilder.Build<bool, string>(Kind, Options, TransformToString);

                if (Options.Input1Type == "int" && Options.Output1Type == "bool") return BlockBuilder.Build<int, bool>(Kind, Options, TransformToBool);
                if (Options.Input1Type == "int" && Options.Output1Type == "string") return BlockBuilder.Build<int, string>(Kind, Options, TransformToString);

                if (Options.Input1Type == "string" && Options.Output1Type == "int") return BlockBuilder.Build<string, int>(Kind, Options, TransformToInt);
                if (Options.Input1Type == "string" && Options.Output1Type == "bool") return BlockBuilder.Build<string, bool>(Kind, Options, TransformToBool);

BlockBuilder看起来像这样：

public static IDataflowBlock Build<TIn, TOut>(string kind, BlockOptions blockOptions, Func<TIn, TOut> singleOutputExecutionFunction = null, Func<TIn, IEnumerable<TOut>> multipleOutputExecutionFunction = null)
    {
        if (singleOutputExecutionFunction == null && multipleOutputExecutionFunction == null)
            throw new ArgumentException("Missing function to execute");

        Enum.TryParse(kind, out TransformationBlocks Kind);

        switch (Kind)
        {
            case TransformationBlocks.Undefined:
                throw new ArgumentException("No block type was specified");
            case TransformationBlocks.TransformBlock:
                return new TransformBlock<TIn, TOut>(param => { return singleOutputExecutionFunction(param); }, new ExecutionDataflowBlockOptions()
                {
                    MaxMessagesPerTask = blockOptions.MaxMessagesPerTask,
                    BoundedCapacity = blockOptions.BoundedCapacity,
                    MaxDegreeOfParallelism = blockOptions.MaxDegreeOfParallelism,
                });
            case TransformationBlocks.TransformManyBlock:
                return new TransformManyBlock<TIn, TOut>(param => { return multipleOutputExecutionFunction(param); }, new ExecutionDataflowBlockOptions()
                {
                    MaxMessagesPerTask = blockOptions.MaxMessagesPerTask,
                    BoundedCapacity = blockOptions.BoundedCapacity,
                    MaxDegreeOfParallelism = blockOptions.MaxDegreeOfParallelism,
                });
            default:
                return default;
        }
    }

和代表/功能看起来像这样：

    private static T TransformToSelf<T>(T obj)
    {
        return obj;
    }

    private static string TransformToString<T>(T obj)
    {
        return Convert.ToString(obj);
    }

    private static int TransformToInt<T>(T obj)
    {
        return Convert.ToInt32(obj);
    }

    private static bool TransformToBool<T>(T obj)
    {
        return Convert.ToBoolean(obj);
    }

Answer 1

这不容易，但是可行。

如果您可以将Input1Type和Input2Type的类型更改为System.Type而不是字符串，则容易得多。

如果没有，那么我建议您创建一个@neil所建议的映射函数，该函数将字符串映射到类型，然后使用MethodInfo.MakeGenericType()调用您的Build()函数。

请参见下面的MakeGenericType()的简单示例。

using System;
using System.Reflection;

namespace make_generic_type
{
    class Program
    {
        static void Main(string[] args)
        {
            // Normal C# usage
            var host = new Host();
            Console.WriteLine(host.GenericMethod<int, string>("Test"));

            // Use reflection to get type definition
            var unboundMethod = typeof(Host).GetMethod(nameof(Host.GenericMethod));
            // As the method is generic, you need to pass the type parameters in.
            // We do this by binding the type parameters with MethodInfo.MakeGenericMethod();
            var boundMethod = unboundMethod.MakeGenericMethod(new Type[]{ typeof(int), typeof(string) });

            // Now we have a method that we can invoke via reflection as normal
            Console.WriteLine(boundMethod.Invoke(new Host(), new object[]{ "Test"}));
        }


    }

    class Host{
        public string GenericMethod<TIn, TOut>(string kind)
        {
            return $"{typeof(TIn).Name}; {typeof(TOut).Name}; {kind};";
        }
    }
}