CODEWITHSUNDEEP
c#.netsystem.reflection
Sandy
Sandy

Reputation: 231

How to check if a given value exists in list of constants

I have a class called Department which contains some constants, I need a method to check if a given value exists in this constants list.

public static class Department
{
  #region Public Constants
   
    public const int Paperback = 1;
    public const int Hardcover = 2;
    public const int Music = 3;

  #endregion
}

Now in another class I'm using or verify/passing values like below the value.

int? Dept = 4;
var availableDepartment= Department.Exists(Dept.Value);

Here availableDepartment should return false since 4 does not exists as department Constants.

I'm looking for an Exists method in class to check if value 4 exists as constants or not.

Please someone help on this.

Upvotes: 0

Views: 96

Answers (3)

wohlstad
wohlstad

Reputation: 28774

As mentioned by others, using reflection is quite an overkill and this problem can be solved in other ways.

However if for some reason you cannot use the other methods, and you must use reflection (since you explicitly tagged system.reflection), here is a way to do this:

using System;
using System.Collections.Generic;
using System.Linq;
using System.Reflection;

namespace Test
{
    public class Util
    {
        // Get the public constants of a type:
        public static List<FieldInfo> GetPublicConstants(Type type)
        {
            FieldInfo[] fieldInfos = type.GetFields(BindingFlags.Public | BindingFlags.Static | BindingFlags.FlattenHierarchy);
            return fieldInfos.Where(fi => fi.IsLiteral && !fi.IsInitOnly).ToList();
        }
    }
        
    public static class Department
    {
        public const int Paperback = 1;
        public const int Hardcover = 2;
        public const int Music = 3;

        public static bool Exists(int departmentNum)
        {
            var constants = Util.GetPublicConstants(typeof(Department));
            foreach (var constant in constants)
            {
                if ((int)constant.GetRawConstantValue() == departmentNum)
                {
                    return true;
                }
            }
            return false;
        }
    }

    class Program
    {
        private static void CheckDepartment(int departmentNum)
        {
            bool bExists = Department.Exists(departmentNum);
            Console.WriteLine("Department {0} exists: {1}", departmentNum,  bExists ? "yes" : "no");
        }

        static void Main(string[] args)
        {
            CheckDepartment(1);
            CheckDepartment(4);
        }
    }
}

Output:

Department 1 exists: yes
Department 4 exists: no

Notes:

  1. class Util with the method GetPublicConstants is general and can be used for any type.
  2. In Department.Exists method I assumed all the constants are ints, if this is not the actual case you need to cast the value to the proper type.
  3. The usage of Department.Exists is demostrated in the test method CheckDepartment.

Live demo

Upvotes: 2

Unknown Coder
Unknown Coder

Reputation: 392

You can use an enum and set it to your constants.

public static class Department {

    private enum DepartmentEnum
    {
        Paperback = 1,
        Hardcover = 2,
        Music = 3,
    }

    public const int Paperback = (int)DepartmentEnum.Paperback;
    public const int Hardcover = (int)DepartmentEnum.Hardcover;
    public const int Music = (int)DepartmentEnum.Music;
  
    public static bool Exists(int value) {
        return Enum.IsDefined<DepartmentEnum>(value);
    }

}

This solution relies on you defining each constant both in the class and in the enum. I don't know what is your use case nor the reason for your constraint on not using enums, but this should work, unless you have some other constraint you did not mention in the question.

Upvotes: 1

derpirscher
derpirscher

Reputation: 17397

If you can't use enum (which nonetheless should be the preferred way of doing such things), how about the straight forward way of implementing a static method in the static class Department? No need for reflection, because if you add an additional value to the Department class you can also adapt the Exists method ...

public static class Department {

  public const int Paperback = 1;
  public const int Hardcover = 2;
  public const int Music = 3;
  
  public static bool Exists(int val) {
    return val == Paperback || val == Hardcover || val == Music;
  }
}

which you then can call via

Department.Exists(3);  //returns true
Department.Exists(27); //returns false

See also this fiddle

Upvotes: 1

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