Iterate through properties of a custom enum

Question

Is it possible to iterate through properties of a custom enum?

My custom enum looks like this:

public class Sex
{
    public static readonly Sex Female = new Sex("xx", "Female");

    public static readonly Sex Male = new Sex("xy", "Male");

    internal string Value { get; private set; }

    internal string Description { get; private set; }

    public override string ToString()
    {
        return Value.ToString();
    }

    public string GetDescription()
    {
        return this.Description;
    }

    protected Sex(string value, string description)
    {
        this.Value = value;
        this.Description = description;
    }

I use it to enable an enum to "enumerate" with strings i.e. "xx", "xy"...

My question is if it is possible to iterate though all sexes with the goal to fill a DropDownList ListItems with value and description.

var ddlSex = new DropDownList()

foreach(var sex in typeof(Sex).<some_magic>)
{
    ddlSex.Items.Add(new ListItem(sex.ToString(), sex.GetDescription()));
}

My idea is to solve the problem with the System.Reflection library but I'm sure how.

Reflection is indeed a magical thing, but it's often a major overkill for things like this. Usually, unless a problem explicitly requires reflection - save it as a last resort. — Benesh, Mar 11 '14 at 21:35
Maybe you're right have you any other ideas how I can solve my problem? — Christoph Brückmann, Mar 11 '14 at 21:41
What's a "custom enum"? That doesn't look like any kind of enum. — John Saunders, Mar 11 '14 at 21:45
It's not a real enum. Here it is called a type-safe-enum pattern: http://stackoverflow.com/a/424414/909980 — Christoph Brückmann, Mar 11 '14 at 21:54

score 3 · Accepted Answer · answered Mar 11 '14 at 21:41

3

var list = typeof(Sex).GetFields(BindingFlags.Static | BindingFlags.Public)
            .Select(f => (Sex)f.GetValue(null))
            .ToList();

foreach(var sex in list)
{
    Console.WriteLine(sex.ToString() + ":" + sex.GetDescription());
}

answered Mar 11 '14 at 21:41

L.B

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Definitely the right solution, but as I mentioned in my answer, it's worth organising your code so that the evaluation of list only happens once in your application runtime. – Rob Lyndon Mar 11 '14 at 22:07
@RobLyndon I'll leave that part to the OP since it is not the point of the question. – L.B Mar 11 '14 at 22:13
@RobLyndon It would be nice to use it the way you described but "var sex" contains two elements which are "null" each containing the static members "Female" and "Male". – Christoph Brückmann Mar 11 '14 at 22:20
2

@RobLyndon + Christoph Brückmann, because it depends on the **order** of the fields' initialization. It should be done in a *static* constructor of the class, like `static Sex() { All = ... }` – L.B Mar 11 '14 at 22:26
@L.B You're absolutely right. Thanks a lot (to both of you)! :) – Christoph Brückmann Mar 11 '14 at 22:34

Rob Lyndon · Answer 2 · 2014-03-11T22:00:22.410

When you use reflection, you should try to do it in one hit: usually in a static constructor.

Here, you could do this:

public class Sex
{
    public static readonly List<Sex> All = typeof(Sex).GetFields(BindingFlags.Public | BindingFlags.Static)
        .Where(f => f.FieldType == typeof(Sex))
        .Select(f => (Sex)f.GetValue(null))
        .ToList();

    public static readonly Sex Female = new Sex("xx", "Female");

    public static readonly Sex Male = new Sex("xy", "Male");

    ...
}

Then you can just use Sex.All, and the reflection will only happen once in your runtime. Your invocation will look like this:

foreach(var sex in Sex.All)
{
    this.ddlSex.Items.Add(new ListItem(sex.ToString(), sex.GetDescription()));
}

Iterate through properties of a custom enum

2 Answers2