委托、多播委托、泛型委托Func,Action,Predicate,ExpressionTree

当试图通过一个事件触发多个方法，抽象出泛型行为的时候，或许可以考虑使用委托。

 

  通过委托构造函数或委托变量把方法赋值给委托

        private delegate double DiscountDelegate(double discount);

        private static DiscountDelegate dd = getDiscountRate;

        static void Main(string[] args)

        {

            double discountPercent;

            discountPercent = dd.Invoke(80);

            Console.WriteLine("打折比例是{0}",discountPercent);

            DiscountDelegate dd1 = new DiscountDelegate(getDiscountRate);

            discountPercent = dd1(90);

            Console.WriteLine("打折比例是{0}", discountPercent);

            Console.ReadKey();

        }

        static double getDiscountRate(double discount)

        {

            return (discount/100);

        }

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  多播委托

        private delegate double CalculateDelegate(double x, double y);

        private static CalculateDelegate cd = getPlus;

        static void Main(string[] args)

        {

            double result1 = cd.Invoke(1, 2);

            Console.WriteLine(result1);

            cd += new CalculateDelegate(getMinus);

            double result2 = cd.Invoke(1, 2);

            Console.WriteLine(result2);

            Console.ReadKey();

        }

        static double getPlus(double x, double y)

        {

            return (x + y);

        }

        static double getMinus(double x, double y)

        {

            return (x - y);

        }

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  泛型委托

□ Func<>规定输入输出的泛型委托

    Func<Calculate, double> func = c => c.X*3 + c.Y;

    Calculate calculate = new Calculate(){X = 2,Y=3};

    double result = func(calculate);

    Console.WriteLine(result);

    class Calculate

    {

        public double X { get; set; }

        public double Y { get; set; }

    }       

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□ Action<>规定输入的泛型委托

    ction<string> MyAction = x => Console.WriteLine(x);

     MyAction("Hello World");    

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□ Predicate<>规定输出为bool类型的泛型委托

   string date = "2012/05/10";

    Predicate<string> isDate = d => IsDate(d);

    if (isDate(date))

    {

        Console.WriteLine("有效");

    }

    else

    {

        Console.WriteLine("无效");

    }

    private static bool IsDate(string date)

    {

        DateTime dt;

        return DateTime.TryParse(date, out dt);

    }   

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□ ExpressionTree泛型委托

    //(5+4)-(2-1)

    //5+4

    BinaryExpression exp1 = Expression.MakeBinary(ExpressionType.Add, Expression.Constant(5),Expression.Constant(4));

    //2-1

    BinaryExpression exp2 = Expression.MakeBinary(ExpressionType.Subtract, Expression.Constant(2),Expression.Constant(1));

    //(5+4)-(2-1)

    BinaryExpression resultExp = Expression.MakeBinary(ExpressionType.Subtract, exp1, exp2);

    int result = Expression.Lambda<Func<int>>(resultExp).Compile()();

    Console.WriteLine(result);

    Console.ReadKey();     

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