Most efficient way to parse a flagged enum to a list

Question

I have a flagged enum and need to retrieve the names of all values set on it.

I am currently taking advantage of the enum's ToString() method which returns the elements comma-separated.

public void SetRoles(Enums.Roles role)
{
    IList<Entities.Role> roleList = role.ToString("G").Split(',')
        .Select(r => new Entities.Role(r.Trim()))
        .ToList();
    ...
}

I'm sure there must be a better way than this.

Answer 1

Try this:

public void SetRoles(Enums.Roles role)
{
  List<string> result = new List<string>();
  foreach(Roles r in Enum.GetValues(typeof(Roles)))
  {
    if ((role & r) != 0) result.Add(r.ToString());
  }
}

Answer 2

If you genuinely just want the strings, can't get much simpler than:

string[] flags = role.ToString().Split(',');

This is simpler than using LINQ and is still just a single line of code. Or if you want a list instead of an array as in the sample in the question you can convert the array into a list:

List<string> flags = new List<string>(role.ToString().Split(','));

In my case I needed a generic solution and came up with this:

value.ToString().Split(',').Select(flag => (T)Enum.Parse(typeof(T), flag)).ToList();

Answer 3

Enum.Parse will handle the concatenated values outputted by ToString just fine. Proof using the Immediate window:

? System.Enum.Parse(typeof(System.AttributeTargets), "Class, Enum")
Class | Enum

(the second line is the output, which is different in the debugger/immediate window from the generic Enum.ToString() output).

Answer 4

List<string> GetRoleNames(Roles roles) =>
    Enum.GetValues(typeof(Roles))
        .Cast<Roles>()
        .Where(role => roles.HasFlag(role))
        .Select(role => role.ToString())
        .ToList();

void TestRoleSelection()
{
    var selectedRoles = (Roles)6;
    var roleNames = GetRoleNames(selectedRoles);
    Console.WriteLine(string.Join(",", roleNames));
    // Output: Admin,User
}

[Flags]
enum Roles
{
    SuperAdmin = 1,
    Admin = 2,
    User = 4,
    Anonymous = 8
}

Answer 5

Why do you need a list? Everything is already stored in the flags:

[Flags]
enum Roles
{
    Read = 0x1,
    Write = 0x2,
    Delete = 0x4,
}

Then assign roles:

var roles = Roles.Read | Roles.Write;

And whenever you need to check if a given role has been you don't need to look in a list, but simply look in the roles enumeration:

if ((roles & Roles.Read) == Roles.Read)
{
    // The user has read permission
}
if ((roles & Roles.Write) == Roles.Write)
{
    // The user has write permission
}

Answer 6

Similar answer to Mick's but puts the operations into extensions and fixes/cleans up the extra space character (from the split).

Also as a bonus if the enum has a _ in it, the code changes it to a space.

public static class EnumExtensions
{  
    // Take anded flag enum and extract the cleaned string values.
    public static List<string> ToComparableStrings(this Enum eNum)
        =>  eNum.ToString()
                .Split(',')
                .Select(str => str.ToCleanString())
                .ToList();

    // Take an individual enum and report the textual value.
    public static string ToComparableString(this Enum eNum)
        => eNum.ToString()
               .ToCleanString();

    // Remove any spaces due to split and if `_` found change it to space.
    public static string ToCleanString(this string str)
        => str.Replace(" ", string.Empty)
              .Replace('_', ' ');
}

---

Usage

var single   = PivotFilter.Dollars_Only;
var multiple = PivotFilter.Dollars_Only | PivotFilter.Non_Productive;

                                // These calls return:
single.ToComparableString()     // "Dollars Only"
multiple.ToComparableString()   // "Non Productive,Dollars Only"
multiple.ToComparableStrings()  // List<string>() { "Non Productive", "Dollars Only" }

Enum for Usage

[Flags]
// Define other methods, classes and namespaces here
public enum PivotFilter
{
    Agency = 1,
    Regular = 2,
    Overtime = 4,
    Non_Productive = 8,
    Dollars_Only = 16,
    Ignore = 32
}