Correctly distinguish between bool? and bool in C#

Question

I am trying to find out if a variable is either a simple bool or a Nullable<bool>.

It seems that

if(val is Nullable<bool>)

returns true for both bool and Nullable<bool> variables and

if(val is bool)

also returns true for both bool and Nullable<bool>.

Basically, I am interesting in finding out if a simple bool variable is true OR if a Nullable<bool> variable is not null.

What's the way to do this?

Here is the full code:

List<string> values = typeof(InstViewModel).GetProperties()
                          .Where(prop => prop != "SubCollection" && prop != "ID" && prop != "Name" && prop != "Level")
                          .Select(prop => prop.GetValue(ivm, null))
                          .Where(val => val != null && (val.GetType() != typeof(bool) || (bool)val == true))      //here I'm trying to check if val is bool and true or if bool? and not null
                          .Select(val => val.ToString())
                          .Where(str => str.Length > 0)
                          .ToList();

The InstViewModel object:

 public class InstViewModel
    {
        public string SubCollection { get; set; }
        public string ID { get; set; }
        public string Name { get; set; }
        public string Level { get; set; }
        public bool Uk { get; set; }
        public bool Eu { get; set; }
        public bool Os { get; set; }
        public Nullable<bool> Mobiles { get; set; }
        public Nullable<bool> Landlines { get; set; }
        public Nullable<bool> UkNrs { get; set; }
        public Nullable<bool> IntNrs { get; set; }
}

The point of my code here is to find out if all of the object's values are null (more specifically, to find out any values that are not null and save them in a List<string>). This presents a complication in the lambda expression, however, when trying to distinguish between bool and bool? types in my object (second Where statement).

Additionally, since the object contains some string types as well, I am trying to exclude those in my first .Where statement (which I am probably not doing right at present as it doesn't seem to be working). But my main goal is to distinguish between bool and bool? types.

Answer 1

There is a simple way to check whether a variable is declared as T or T?:

private static bool IsNullable<T>(T val)
{
    return false;
}

private static bool IsNullable<T>(T? val)
    where T : struct
{
    return true;
}

Usage:

bool? val = false;

if (IsNullable(val))
{
    ...
}

EDIT
Try the following code for edited question:

var boolProps = typeof (InstViewModel).GetProperties()
    .Where(prop => prop.PropertyType == typeof(bool))
    .Select(prop => (bool)prop.GetValue(ivm, null))
    .Select(v => v ? v.ToString() : String.Empty);

var nullableBoolProps = typeof(InstViewModel).GetProperties()
    .Where(prop => prop.PropertyType == typeof(bool?))
    .Select(prop => (bool?)prop.GetValue(ivm, null))
    .Select(v => v.HasValue ? v.ToString() : String.Empty);

List<string> values = boolProps.Concat(nullableBoolProps)
              .Where(str => str.Length != 0)
              .ToList();

Answer 2

Code for getting class instance values:

// create class instance
InstViewModel model = new InstViewModel()
{
    Uk = true,
    UkNrs = false,
};

// check all boolean fields are false or null
bool isAllNullOrFalse = (from property in typeof(InstViewModel).GetProperties()
                         let type = property.PropertyType
                         let isBool = type == typeof(bool)
                         where isBool || type == typeof(bool?)
                         let value = property.GetValue(model)
                         select value == null || (isBool && bool.Equals(value, false))).All(e => e);

Console.WriteLine("All values are null or false = {0}", isAllNullOrFalse);