如何将方法存储在哈希表中？

Question

我正在尝试将方法列表存储在 C# 中的哈希表中，以便在用户输入所需的密钥后立即执行该方法。我想知道我将如何做到这一点。有人告诉我，我可以同时使用匿名接口或委托来执行此操作。哪个更好？为什么？不过，我还没有找到太多关于这实际上是如何完成的参考。

例子：

key = 方法

"+" = object.add

"-" = object.minus

Answer 1

这是一个过于简单的解决方案，但它说明了完成您的要求所需的步骤。

public class Test
{
    // Ok, we declare the hashtable here. It could be a Dictionary though, so we don't have to
    // cast it. But you requested a hashtable.
    private Hashtable hash = new Hashtable();

    // Were it a dictionary, we'd have:
    // private Dictionary<string, Calculation> dict = new Dictionary<string, Calculation>();

    // We declare the signature of the methods that we will store. This means that we accept any
    // methods which receive two decimal parameters and return a decimal output
    private delegate decimal Calculation(decimal x, decimal y);

    public Test()
    {
    }

    public void Run()
    {
        // A sample implementation of the delegate
        Calculation sum = (decimal x, decimal y) =>
        {
            return x + y;
        };

        // Another sample implementation
        Calculation minus = (decimal x, decimal y) =>
        {
            return x - y;
        };

        // Here we add both of them to the hashtable
        this.hash.Add("+", sum);
        this.hash.Add("-", minus);

        // Were it a dictionary, we'd have:
        // this.dict.Add("+", sum);
        // this.dict.Add("+", minus);

        // Note that in the hashtable you can put ANYTHING. Were it a dictionary, it would be strong-typed and
        // we'd be able to only add Calculation types

        // Now ask the user for input values
        Console.Write("X: ");
        var xInput = decimal.Parse(Console.ReadLine());

        Console.Write("Y: ");
        var yInput = decimal.Parse(Console.ReadLine());

        // Ask the user which method to execute
        Console.WriteLine("Which method to execute? Enter number:");
        Console.WriteLine("1. +");
        Console.WriteLine("2. -");
        Console.Write("> ");

        var choice = int.Parse(Console.ReadLine());

        // Get the selected method from the hashtable
        Calculation calc;
        if (choice == 1)
        {
            calc = (Calculation)this.hash["+"];
        }
        else if (choice == 2)
        {
            calc = (Calculation)this.hash["-"];
        }
        else
        {
            throw new ArgumentOutOfRangeException();
        }

        // Were it a dictionary, we'd have (note that we don't have to cast it):
        // calc = this.dict["-"];

        // execute it, and output the result
        Console.WriteLine("Result: " + calc(xInput, yInput));

        Console.ReadKey();
    }
}

Answer 2

在 C# 中存储方法引用有一个类型叫做 Delegate。您应该使用代表字典。首先，您必须定义一个与您的方法签名匹配的委托。想象一下，您有一个返回 int 并接受两个 int 作为参数的方法列表。首先，您为此定义委托。

 public delegate int SomeMethodsHandler(int a,int b);

然后你创建你的方法。

public int MethodA(int a,int b)
{
      // do some work here
      return 0;
}

 public int MethodB(int a,int b)
{
      // do some work here
      return 1;
}

 public int MethodC(int a,int b)
{
      // do some work here
      return 2;
}

然后你创建 Dictionary 来存储这些方法。

 Dictionary<string,SomeMethodsHandler> methods = new Dictionary<string,SomeMethodsHandler>();

 methods["A"] = MethodA;
 methods["B"] = MethodB;
 methods["C"] = MethodC;

再次调用该方法。

 int a = methods["A"](5,7);