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);
}
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);
}
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; }
}
□ Action<>规定输入的泛型委托
ction<string> MyAction = x => Console.WriteLine(x);
MyAction("Hello World");
□ 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);
}
□ 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();