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#region 9-1用匿名方法来创建委托实例 Func<string, int> returnLength;//等价public delegate int SomeDelegate(string arg1)。当返回void时，使用Action<>系列委托 returnLength = delegate(string text) { return text.Length; }; Console.WriteLine(returnLength("Holle")); #endregion #region 9-2冗长的第一个Lambda表达式 Func<string, int> returnLength; returnLength = (string text) => { return text.Length; }; returnLength = (string text) => text.Length;//用单一表达式做为主体 returnLength = (text) => text.Length;//隐式类型的参数列表 returnLength = text => text.Length;//单一参数的快捷语法 Console.WriteLine(returnLength("Holle")); #endregion #region 9-4用Lambda处理一个电影列表 var films = new List<Film> { new Film{Name="Jaws1",Year=1975}, new Film{Name="Jaws2",Year=1975}, new Film{Name="Jaws5",Year=1975}, new Film{Name="Jaws4",Year=1976}, }; Action<Film> print = film => Console.WriteLine("Name={0},Year={1}", film.Name, film.Year); films.ForEach(print);//打印全部元素 films.FindAll(film => film.Year > 1975).ForEach(print);//过滤打印 films.Sort((f1, f2) => f1.Name.CompareTo(f2.Name));//排序打印 films.ForEach(print); #endregionpublic partial class Form1 : Form { public Form1() { InitializeComponent(); Button button = new Button { Text = "Click me" }; button.Click += (src, e) => Log("Click", src, e); button.KeyPress += (src, e) => Log("KeyPress", src, e); button.MouseClick+=(src,e)=>Log("MouseClick",src,e); Form form = new Form { AutoSize = true, Controls = { button } }; Application.Run(form); } static void Log(string title, object sender, EventArgs e) { Console.WriteLine("Event:{0}", title); Console.WriteLine("Sender:{0}", sender); Console.WriteLine("Argument:{0}", e); foreach (PropertyDescriptor prop in TypeDescriptor.GetProperties(e)) { string name = prop.DisplayName; object value = prop.GetValue(e); Console.WriteLine(" {0}={1}", name, value); } } static void Log(string title, object sender) { Console.WriteLine("Event:{0}", title); Console.WriteLine("Sender:{0}", sender); } }#region 9-6一个非常简单的表达式树 //System.Linq.Expressions命名空间包含了代表表达式的各个类，他们都继承至Expression Expression firstArg = Expression.Constant(2); Expression secondArg = Expression.Constant(3); Expression add = Expression.Add(firstArg, secondArg); Console.WriteLine(add); #endregion
#region 9-7编译并执行一个表达式 Expression firstArg = Expression.Constant(2); Expression secondArg = Expression.Constant(3); Expression add = Expression.Add(firstArg, secondArg); Func<int> compiled = Expression.Lambda<Func<int>>(add).Compile(); Console.WriteLine(compiled()); #endregion #region 9-8用Lambda表达式转换成表达式树 Expression<Func<int>> return5 = () => 5;//Lambda表达式 Func<int> compiled1 = return5.Compile(); Console.WriteLine(compiled1()); #endregion#region 9-9演示一个更复杂的表达式树 Expression<Func<string, string, bool>> expression = (x, y) => x.StartsWith(y); var compiled = expression.Compile(); Console.WriteLine(compiled("First", "Second")); Console.WriteLine(compiled("First", "Fir")); #endregion
#region 9-10用代码来构造一个方法调用表达式树 MethodInfo method = typeof(string).GetMethod("StartsWith", new[] { typeof(string) });//获取方法名为StartsWith，参数为string的公共方法 var target = Expression.Parameter(typeof(string), "x"); var methodArg = Expression.Parameter(typeof(string), "y"); Expression[] methodArgs = new[] { methodArg }; //Call(Expression instance, MethodInfo method, params Expression[] arguments) Expression call = Expression.Call(target, method, methodArgs);//x.StartsWith(y),以上部件创建CallExpression var lambdaParameters = new[] { target, methodArg };//这里使用的参数顺序就是调用委托所使用的参数顺序 var lambda = Expression.Lambda<Func<string, string, bool>>(call, lambdaParameters);//(x,y)=>x.StartsWith(y),lambdaParameters填充call集合 var compiled = lambda.Compile();//生成lambda表达式的委托 Console.WriteLine(compiled("First", "csend")); Console.WriteLine(compiled("First", "Fir")); #endregion #region 9-11 需要新的类型推断规则例子（用Lambda表达式调用一个泛型方法） static void PrintConvertedValue<TInput, TOutput>(TInput input, Converter<TInput, TOutput> converter) { Console.WriteLine(converter(input)); } #endregion #region 9-11 PrintConvertedValue("I‘m a string", x => x.Length);//C#2中，编译将失败，C#2类型推断单独针对每一个实参来进行的，从一个实参无法推断出另一个实参 #endregion #region 9-13根据一天当中的时间来选择返回int或object delegate T MyFunc<T>(); static void WriteResult<T>(MyFunc<T> function) { Console.WriteLine(function()); } #endregion #region 9-13 WriteResult(delegate { if (DateTime.Now.Hour < 22)//int { return 10; } else//object { return new object(); } });//编译器采用处理隐式数组的逻辑处理返回类型，对int进行了装箱，返回类型为object #endregion #region 9-14综合来自多个实参的信息，灵活地进行类型推断 static void PrintType<T>(T first, T second)//被强制转换为具体类型参数的最终固定变量类型 { Console.WriteLine(typeof(T)); } #endregion #region 9-14 PrintType(1,new object());//返回类型推断为object类型 #endregion
#region 9-15多级类型推断 static void ConvertTwice<TInput, TMiddle, TOutput>(TInput input, Converter<TInput, TMiddle> firstConversion, Converter<TMiddle, TOutput> secondConversion) { TMiddle middle = firstConversion(input); TOutput output = secondConversion(middle); Console.WriteLine(output); } #endregion #region 9-15 //第一阶段，编译器处理普通实参，得到TInput类型string，第一次执行阶段二，TInput固定为string类型，推断TMiddle为int，再次执行第二阶段，TMiddle固定为int，TOutput为double，推断结束 //lambda表达式主体只有在输入参数的类型已知后才能进行检查 ConvertTwice("Another string", text => text.Length, length => Math.Sqrt(length)); #endregion #region 9-16委托返回类型影响了重载选择 //如果一个匿名函数能转换成参数列表相同，但返回类型不同的两个委托类型，就根据从“推断的返回类型”到“委托的返回类型”的转换来判断哪个委托转换好 static void Execute(Func<int> action) { Console.WriteLine("action return an int:" + action()); } static void Execute(Func<double> action) { Console.WriteLine("action return a douban:" + action()); } #endregion #region 9-16 Execute(() => 1); #endregion
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原文地址：http://www.cnblogs.com/Tan-sir/p/5169217.html
