C#中的Action<>和Func<>

来源：互联网发布：编程打印空心字符菱形编辑：程序博客网时间：2024/04/26 08:33

其实他们两个都是委托【代理】的简写形式。

一、【action<>】指定那些只有输入参数，没有返回值的委托

Delegate的代码：

[csharp]

public delegate void myDelegate(string str);

public static void HellowChinese(string strChinese)

{

Console.WriteLine("Good morning," + strChinese);

Console.ReadLine();

}

myDelegate d = new myDelegate(HellowChinese);

d("Mr wang");

用了Action之后呢：

[csharp]

public static void HellowChinese(string strChinese)

{

Console.WriteLine("Good morning," + strChinese);

Console.ReadLine();

}

Action<string> action = HellowChinese;

action("Spring.");

就是相当于省去了定义委托的步骤了。

二、func<> 这个和上面的那个是一样的，区别是这个有返回值！

[csharp]

public static string HelloEnglish(string strEnglish)

{

return "Hello." + strEnglish;

}

Func<string, string> f = HelloEnglish;

Console.WriteLine(f("Srping ji"));

Console.ReadLine();

private void button5_Click(object sender, EventArgs e)
        {
            //类似委托功能
            Func<string, int> test = TsetMothod;

Console.WriteLine(test("123"));

Func<string, int> test1 = TsetMothod;

//只需要调用这个类就可以减少重复的代码
CallMethod<string>(test1, "123");

//或者采用这种
CallMethod<string>(new Func<string, int>(TsetMothod), "123");

CallMethod(new Func<string, int>(TsetMothod), "123");

}

public static void CallMethod<T>(Func<T, int> func, T item)
        {
            try
            {
                int i = func(item);
                Console.WriteLine(i);
            }
            catch (Exception e)
            {

            }
            finally
            {

}
}

        public static int TsetMothod(string name)
        {
            if (string.IsNullOrEmpty(name))
            {
                return 1;
            }
            return 0;

}

----------------------------------Func例-------------------------------------------

private void button6_Click(object sender, EventArgs e)
        {
                 // Note that each lambda expression has no parameters.
              LazyValue<int> lazyOne = new LazyValue<int>(() => ExpensiveOne());
              LazyValue<long> lazyTwo = new LazyValue<long>(() => ExpensiveTwo("apple"));

Console.WriteLine("LazyValue objects have been created.");

              // Get the values of the LazyValue objects.
              Console.WriteLine(lazyOne.Value);
              Console.WriteLine(lazyTwo.Value);

}

         static int ExpensiveOne()
           {
              Console.WriteLine("\nExpensiveOne() is executing.");
              return 1;
           }

       static long ExpensiveTwo(string input)
       {
          Console.WriteLine("\nExpensiveTwo() is executing.");
          return (long)input.Length;
       }

}

    class LazyValue<T> where T : struct
    {
        private Nullable<T> val;
        private Func<T> getValue;

        // Constructor.
        public LazyValue(Func<T> func)
        {
            val = null;
            getValue = func;
        }

        public T Value
        {
            get
            {
                if (val == null)
                    // Execute the delegate.
                    val = getValue();
                return (T)val;
            }
        }
    }