如何使用表达式构建匿名类型? [英] How to use Expression to build an Anonymous Type?

问题描述

在C#3.0中，您可以使用Expression使用以下语法创建一个类:

In C# 3.0 you can use Expression to create a class with the following syntax:

var exp = Expression.New(typeof(MyClass));
var lambda = LambdaExpression.Lambda(exp);
object myObj = lambda.Compile().DynamicInvoke();

但是您如何使用Expression创建一个匿名类呢?

But how do you use Expression to create an Anonymous class?

//anonymousType = typeof(new{ Name="abc", Num=123});
Type anonymousType = Expression.NewAnonymousType???  <--How to do ?
var exp = Expression.New(anonymousType);
var lambda = LambdaExpression.Lambda(exp);
object myObj = lambda.Compile().DynamicInvoke();

推荐答案

您已经关闭，但是您必须知道匿名类型没有默认的构造函数.以下代码显示{ Name = def, Num = 456 }:

You're close, but you have to be aware that anonymous types don't have default constructors. The following code prints { Name = def, Num = 456 }:

Type anonType = new { Name = "abc", Num = 123 }.GetType();
var exp = Expression.New(
            anonType.GetConstructor(new[] { typeof(string), typeof(int) }),
            Expression.Constant("def"),
            Expression.Constant(456));
var lambda = LambdaExpression.Lambda(exp);
object myObj = lambda.Compile().DynamicInvoke();
Console.WriteLine(myObj);

如果您不必创建许多这种类型的实例，那么Activator.CreateInstance也会做得很好(一些实例更快，但许多实例则慢).这段代码显示{ Name = g Num = 789 }:

If you don't have to create many instances of this type, Activator.CreateInstance will do just as well (it's faster for a few instances, but slower for many). This code prints { Name = g Num = 789 }:

Type anonType = new { Name = "abc", Num = 123 }.GetType();
object myObj = Activator.CreateInstance(anonType, "ghi", 789);
Console.WriteLine(myObj);

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