How to use reflection to get generic lists of a particular type

Question

How do I use .NET reflection to get a list of properties that are of a particular class, including generic lists, e.g. I have a class that looks like this:

class Test
{
    [NotConditional()]
    [Order( 1 )]
    public Value Name { get; set; }

    [NotConditional()]
    [Order( 2 )]
    public Value Address { get; set; }

    [NotConditional()]
    [Order( 3 )]
    public List<Value> Contacts { get; set; }
}

I want to get the Name, Address and Contacts properties as all of them are of type Value.

I have the following code, which works great, but I want the List<> bit to only pick up List<Value> properties.

var props = from p in this.GetType().GetProperties()
            where p.PropertyType.IsSubclassOf( typeof( Std ) ) ||
            ( p.PropertyType.IsGenericType &&
              p.PropertyType.GetGenericTypeDefinition() == typeof( List<> ) )
              select new { Property = p };

I have tried:

var props = from p in this.GetType().GetProperties()
            where p.PropertyType.IsSubclassOf( typeof( Std ) ) ||
            ( p.PropertyType.IsGenericType &&
              p.PropertyType.GetGenericTypeDefinition() == typeof( List<Value> ) )
              select new { Property = p };

But, it doesn't pick up any List<Value> properties and only picks up Name and Address properties.

** UPDATE **

I have included these two classes as well as I also want to include properties that also derive from Std'.

class Std
{
    public int id { get; set; }
}

class Value : Std
{
    public string Val { get; set; }
}

Why are you using GetGenericTypeDefinition when you don't actually want the generic type definition? — Jon Skeet
– Jon Skeet, Commented Jul 25, 2014 at 14:57
@JonSkeet That's because I found this code on a Stack Overflow post and used it as it's what I was looking for only that it did'nt pick up the List<Value> properties I also wanted. — Intrepid
– Intrepid, Commented Jul 25, 2014 at 14:59
In future, it's worth making sure that you thoroughly understand code from elsewhere before using it. I suspect you were looking at code which was trying to find properties of any list type, hence the call to GetGenericTypeDefinition. — Jon Skeet
– Jon Skeet, Commented Jul 25, 2014 at 15:01
@JonSkeet That's an excellent lesson to learn. I did understand what the code was doing, but misinterpreted the reasoning of the GetGenericTypeDefinition method call. — Intrepid
– Intrepid, Commented Jul 25, 2014 at 15:02

p.s.w.g · Accepted Answer · 2014-07-25 15:15:45Z

4

Seems pretty straightforward. Try this:

var props = from p in this.GetType().GetProperties()
            where p.PropertyType == typeof(Value) ||
                  p.PropertyType == typeof(List<Value>)
            select new { Property = p };

Or to handle subclasses of Value or List<Value>

var props = from p in this.GetType().GetProperties()
            where typeof(Value).IsAssignableFrom( p.PropertyType ) ||
                  typeof(List<Value>).IsAssignableFrom( p.PropertyType )
            select new { Property = p };

Given your update, if you want to get any property whose type is assignable from Std or is a list whose parameter is assignable from Std, that's a bit more difficult because List<T> is invariant with respect to T. If that's what you want, you can do something like this:

var props = from p in this.GetType().GetProperties()
            where typeof(Std).IsAssignableFrom( p.PropertyType ) ||
                  ( p.PropertyType.IsGenericType &&
                    p.PropertyType.GetGenericTypeDefinition() == typeof(List<>) && 
                    typeof(Std).IsAssignableFrom( p.PropertyType.GetGenericArguments()[0] ) )
            select new { Property = p };

^{Note that this version doesn't return properties whose types inherit from List<Std>.}

edited Jul 25, 2014 at 15:15

answered Jul 25, 2014 at 14:56

p.s.w.g

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2 Comments

Intrepid Over a year ago

I am aware of this. A List<Value> is never going to be assigned to a List<Std> but I have other properties that derive from Std and would like them picked up as well as Value classes.

p.s.w.g Over a year ago

@Mike See my updated answer for an alternative solution that might work in your situation.

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