Is it possible to get all properties of <T> in their declaration order (or any other order)?

Question

Getting properties of a class in order, I've tried with Attribute and is ok:

[AttributeUsage(AttributeTargets.Property, AllowMultiple = false, Inherited = false)]
public sealed class MyAttribute: Attribute
{
    public int Index { get; set; }
}

public class AnyClass
{
    [Campo(Index = 2)]
    public int Num { get; set; }

    [Campo(Index  = 0)]
    public string Name { get; set; }

    [Campo(Index = 1)]
    public DateTime EscDate { get; set; }
}

// then I get properties in order
var props = (from pro in (new AnyClass()).GetType().GetProperties()
             let att = pro.GetCustomAttributes(false).Cast<MyAttribute>().First()
             let order = att.Index
             orderby order ascending
             select pro).ToArray();
// result:
// string   Name
// DateTime EscDate
// int      Num

but, is it possible to get them, when <T> is unknown

var props = typeof(T).GetProperties(); // ... order here!

When doing this, not always is the same order, how to set it if you don't know that <T> has attributes or not?, is there any other method?

Answer 1

You can't get the declaration order (ie the order they are in the code), since that's not saved when the code is compiled. If all you need is a consistent order, just order by the property name:

var props = (from pro in typeof(T).GetProperties()
             orderby pro.Name
             select pro).ToArray();

If you want to use MyAttribute if it's there, you might do something like this:

var pairs = (from pro in typeof(T).GetProperties()
             let att = pro.GetCustomAttributes(false)
                          .Cast<MyAttribute>().FirstOrDefault()
             select new { pro, att }).ToList();
IList<PropertyInfo> props;
if (pairs.All(x => x.att != null))
    props = (from pair in pairs
             let order = pair.att.Index
             orderby order ascending
             select pair.pro).ToList();
else
    props = (from pair in pairs
             orderby pair.pro.Name
             select pair.pro).ToList();