使用防爆pressions获得获取财产Acessor [英] Using Expressions to get a Get Acessor of a property

问题描述

我想要得到的获取属性的Acessor（的PropertyInfo ），并将其编译成 Func键＆LT;对象，对象＆gt; 。声明类型仅在运行时称。

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.

我目前的code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，我必须把＆LT;对象，对象＆gt; 作为泛型参数，因为有时候我会得到的键入<属性/ code>，如的typeof（T）.GetProperties（）[0] .GetProperties（），其中第一个的GetProperties（）[]返回一个自定义类型的对象，我必须体现出这一点。

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code，我获得OS 3.0的错误：

When I run the code above, I getthis 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]]'.

所以，我能做些什么来返回 Func键＆LT;对象，对象＆gt;

推荐答案

您可以添加类型转换预期的类型和使用的返回类型防爆pression.Convert ：

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();
}

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