使用表达式获取属性的 Get Acessor [英] Using Expressions to get a Get Acessor of a property

问题描述

我想获取属性的获取访问器 (PropertyInfo) 并将其编译为 Func.声明类型仅在运行时已知.

I want to get the Get Acessor of a Property (PropertyInfo) and compile it to a Func<object,object>. The declaring type is only known at runtime.

我当前的代码是:

public Func<Object, Object> CompilePropGetter(PropertyInfo info)
{
    MethodInfo getter = info.GetGetMethod();

    ParameterExpression instance = Expression.Parameter(info.DeclaringType, info.DeclaringType.Name);

    MethodCallExpression setterCall = Expression.Call(instance, getter);

    Expression getvalueExp = Expression.Lambda(setterCall, instance);


    Expression<Func<object, object>> GetPropertyValue = (Expression<Func<object, object>>)getvalueExp;
    return GetPropertyValue.Compile();

}

不幸的是，我不得不把作为通用参数，因为有时我会得到一个Type的属性，比如typeof(T).GetProperties()[0].GetProperties()，其中第一个 GetProperties()[] 返回一个自定义类型的对象，我必须反映它.

Unfortunately, I have to put <Object,Object> as generic parameters, because sometimes I will get the properties of a Type, like typeof(T).GetProperties()[0].GetProperties(), where the first GetProperties()[] returns a custom-type object, and I have to reflect it.

当我运行上面的代码时，我得到这个错误:

When I run the code above, I get this error:

Unable to cast object of type 'System.Linq.Expressions.Expression`1[System.Func`2[**CustomType**,**OtherCustomType**]]' to type 'System.Linq.Expressions.Expression`1[System.Func`2[System.Object,System.Object]]'.

那么，我该怎么做才能返回 Func?

So, what can I do to return a Func<Object,Object>?

推荐答案

您可以使用 Expression.Convert 将强制转换添加到预期类型和返回类型:

You can add casts to the expected type and from the return type using Expression.Convert:

public static Func<Object, Object> CompilePropGetter(PropertyInfo info)
{
    ParameterExpression instance = Expression.Parameter(typeof(object));
    var propExpr = Expression.Property(Expression.Convert(instance, info.DeclaringType), info);
    var castExpr = Expression.Convert(propExpr, typeof(object));
    var body = Expression.Lambda<Func<object, object>>(castExpr, instance);
    return body.Compile();
}

这篇关于使用表达式获取属性的 Get Acessor的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！