問題描述
如何在 C# 中使用“param”來獲取這個示例？ (How can I get this example using "param" in C# to work?)
I am trying to understand the meaning and use of the param parameter in this line taken from a RelayCommand example:
return new RelayCommand(param => MessageBox.Show("It worked."));
First, I understand that the "param" parameter has nothing to do with the "params" keyword, is this correct?
public int Add(params int[] list)
{
int sum = 0;
foreach (int i in list)
sum += i;
return sum;
}
Second, what kind of delegate code do I have to add to get the following example to work?
using System;
using System.Collections.Generic;
namespace TestParam222
{
class Program
{
static void Main(string[] args)
{
Console.WriteLine("The total is {0}.", Tools.GetTest(param => 23));
Console.ReadLine();
}
}
class Tools
{
public static string GetTest(List<int> integers)
{
return "ok";
}
}
}
‑‑‑‑‑
參考解法
方法 1:
param isn't a keyword. It's the parameter for a lambda expression in your sample. You'd need to make your method take a delegate or an expression tree, e.g.
using System;
using System.Collections.Generic;
namespace TestParam222
{
class Program
{
static void Main(string[] args)
{
Console.WriteLine("The total is {0}.", Tools.GetTest(param => 23));
Console.ReadLine();
}
}
class Tools
{
public static string GetTest(Func<int, int> integers)
{
return "ok";
}
}
}
The Func<int,int> could actually be any Func<T,int> (or Func<T,long> etc) because your lambda expression doesn't use param anywhere. Alternatively it could be an Expression<Func<int,int>> etc.
I suggest you read up on lambda expressions for more details, for instance in any of these SO questions:
- Can you explain lambda expressions
- What is a lambda
- C# lambda expression, why should I use this
(by Edward Tanguay、Jon Skeet)