Access the value of a member expression

Access the value of a member expression

解答1

You can compile and invoke a lambda expression whose body is the member access:

private object GetValue(MemberExpression member)
{
    var objectMember = Expression.Convert(member, typeof(object));

    var getterLambda = Expression.Lambda<Func<object>>(objectMember);

    var getter = getterLambda.Compile();

    return getter();
}

Local evaluation is a common technique when parsing expression trees. LINQ to SQL does this exact thing in quite a few places.

 

 解答2

MemberExpression right = (MemberExpression)((BinaryExpression)p.Body).Right;
 Expression.Lambda(right).Compile().DynamicInvoke();

 会有同样的问题

 

尝试gist

https://gist.github.com/jcansdale/3d4b860188723ea346621b1c51fd8461#file-expressionutilities-cs-L13

UKERecognition.Infrastructure.Exceptions.UIException: UserInterface ---> System.Exception: Couldn't evaluate Expression without compiling: l

 

 

尝试Lambda表达式公共操作类(二)

  private static object GetMemberValue(MemberExpression expression)
        {
            if (expression == null)
                return null;
            var field = expression.Member as FieldInfo;
            if (field != null)
            {
                var constValue = GetConstantValue(expression.Expression);
                return field.GetValue(constValue);
            }
            var property = expression.Member as PropertyInfo;
            if (property == null)
                return null;
            var value = GetMemberValue(expression.Expression as MemberExpression);
            return property.GetValue(value);
        }

        private static object GetConstantValue(Expression expression)
        {
            var constantExpression = expression as ConstantExpression;
            if (constantExpression == null)
                return null;
            return constantExpression.Value;
        }

System.Reflection.TargetException: Non-static method requires a target.
at System.Reflection.RuntimeMethodInfo.CheckConsistency(Object target)
at System.Reflection.RuntimeMethodInfo.InvokeArgumentsCheck(Object obj, BindingFlags invokeAttr, Binder binder, Object[] parameters, CultureInfo culture)
at System.Reflection.RuntimeMethodInfo.Invoke(Object obj, BindingFlags invokeAttr, Binder binder, Object[] parameters, CultureInfo culture)
at System.Reflection.RuntimePropertyInfo.GetValue(Object obj, Object[] index)
at LISA.Custom.Infrastructure.LisaExpressionVisitor`1.GetMemberValue(MemberExpression expression) in

 

作者:Chuck Lu    GitHub