Console.WriteLine("***********************************************");            {                //1.0获取方法                MethodInfo method = typeof(string).GetMethod("Substring", new[] { typeof(int), typeof(int) });                //2.0构造表达式树的参数                ParameterExpression target = Expression.Parameter(typeof(string), "s");                ParameterExpression firstParam = Expression.Parameter(typeof(int), "a");                ParameterExpression secondParam = Expression.Parameter(typeof(int), "b");                //3.0构造方法的参数                Expression[] methodArgs = new[] { firstParam, secondParam };                Expression call = Expression.Call(target, method, methodArgs);                Console.WriteLine(call);//  s.Substring(a,b);                //4.0将表达式树的参数构造成 lambda表达式的参数                var lambdaParam = new[] { target, firstParam, secondParam };                foreach (var parameterExpression in lambdaParam)                {                    Console.WriteLine(parameterExpression);//s,a,b                }                //5.0构造 lambda表达式树                var lambda = Expression.Lambda
     
      
       >(call, lambdaParam);                Console.WriteLine(lambda);//    (s,a,b)=>s.Substring(a,b);                //6.0将 lambda表达式树转换成 lambda表达式                var compile = lambda.Compile();                //7.0执行委托                var result = compile("wjire", 0, 3);                Console.WriteLine(result);            }            Console.WriteLine("***********************************************");            {                //1.0获取方法                MethodInfo method = typeof(string).GetMethod("Substring", new[] { typeof(int), typeof(int) });                //2.0构造表达式树的参数                ParameterExpression target = Expression.Parameter(typeof(string), "s");                //2.5设置表达式树的常量                ConstantExpression firstParam = Expression.Constant(0);                ConstantExpression secondParam = Expression.Constant(3);                //3.0构造方法的参数                Expression[] methodArgs = new[] { firstParam, secondParam };                Expression call = Expression.Call(target, method, methodArgs);                Console.WriteLine(call);//  s.Substring(0,3);                //4.0将表达式树的参数构造成 lambda表达式的参数                var lambdaParam = new[] { target };                foreach (var parameterExpression in lambdaParam)                {                    Console.WriteLine(parameterExpression);//s                }                //5.0构造 lambda表达式树                var lambda = Expression.Lambda
       
        
         >(call, lambdaParam);                Console.WriteLine(lambda);//    s=>s.Substring(0,3);                //6.0将 lambda表达式树转换成 lambda表达式                var compile = lambda.Compile();                //7.0执行委托                var result = compile("wjire");                Console.WriteLine(result);            }            Console.WriteLine("***********************************************");            {                PropertyInfo property = typeof(Person).GetProperty("Id");                var target = Expression.Parameter(typeof(Person), "p");                var pro = Expression.Property(target, property);                Console.WriteLine(pro);//   p.Id                var lambdaParam = new[] { target };                var lambda = Expression.Lambda
         
          
           >(pro, lambdaParam); Console.WriteLine(lambda);// p=>p.Id var compile = lambda.Compile(); var result = compile(new Person { Id = 123 }); Console.WriteLine(result); }