通过反射创建通用功能 [英] Create generic Func from reflection

问题描述

我在变量中指定了类型: Type hiddenType .我需要创建一个 Func< T> 委托，其中 T 是上述变量中​​指定的类型，并分配一个方法:

I've specified type in a variable: Type hiddenType. I need to create a Func<T> delegate where T is of type specified in mentioned variable and assign an method:

var funcType = typeof(Func<>).MakeGenericType(hiddenType);
Func<object> funcImplementation = () => GetInstance(hiddenType);

var myFunc= Delegate.CreateDelegate(funcType , valueGenerator.Method);

它不起作用-因为 funcImplementation 返回的是 object ，而不是所需的.在运行时，它肯定是 hiddenType 中指定的类型的实例.

It doesn't works - because funcImplementation is returns object instead of desired. At runtime, it will surely be an instance of type specified in hiddenType.

GetInstance 返回 object ，并且不能更改签名.

GetInstance returns object and signaure cannot be changed.

推荐答案

您可以通过手动构建表达式树并将类型转换插入 hiddenType 来解决此问题.构造表达式树时，这是允许的.

You can solve this by building an expression tree manually, and inserting a cast to hiddenType. This is allowed when you construct an expression tree.

var typeConst = Expression.Constant(hiddenType);
MethodInfo getInst = ... // <<== Use reflection here to get GetInstance info
var callGetInst = Expression.Call(getInst, typeConst);
var cast = Expression.Convert(callGetInst, hiddenType);
var del = Expression.Lambda(cast).Compile();

注意:以上代码假定 GetInstance 是 static .如果不是静态的，则更改构造 callGetInst 的方式以传递在其上调用方法的对象.

Note: the above code assumes that GetInstance is static. If it is not static, change the way you construct callGetInst to pass the object on which the method is invoked.

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