How to know if a PropertyInfo is a collection

Question

Below is some code I use to get the initial state of all public properties in a class for IsDirty checking.

What's the easiest way to see if a property is IEnumerable?

Cheers,
Berryl

  protected virtual Dictionary<string, object> _GetPropertyValues()
    {
        return _getPublicPropertiesWithSetters()
            .ToDictionary(pi => pi.Name, pi => pi.GetValue(this, null));
    }

    private IEnumerable<PropertyInfo> _getPublicPropertiesWithSetters()
    {
        return GetType().GetProperties().Where(pi => pi.CanWrite);
    }

UPDATE

What I wound up doing was adding a few library extensions as follows

    public static bool IsNonStringEnumerable(this PropertyInfo pi) {
        return pi != null && pi.PropertyType.IsNonStringEnumerable();
    }

    public static bool IsNonStringEnumerable(this object instance) {
        return instance != null && instance.GetType().IsNonStringEnumerable();
    }

    public static bool IsNonStringEnumerable(this Type type) {
        if (type == null || type == typeof(string))
            return false;
        return typeof(IEnumerable).IsAssignableFrom(type);
    }

score 104 · Accepted Answer · edited Feb 08 '22 at 11:09

104

if (typeof(IEnumerable).IsAssignableFrom(prop.PropertyType) && prop.PropertyType != typeof(string))

edited Feb 08 '22 at 11:09

Hans Keﬆing

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answered Aug 25 '10 at 20:12

Fyodor Soikin

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Note that a string is an IEnumerable too – Eric Eijkelenboom Nov 11 '13 at 19:06
27

better: p.PropertyType != typeof(string) && typeof(IEnumerable).IsAssignableFrom(p.PropertyType) – kofifus Jun 29 '18 at 03:09
i use this: typeof(IEnumerable – Bence Végert Dec 12 '22 at 15:22

score 22 · Answer 2 · answered Mar 15 '13 at 11:49

22

I agree with Fyodor Soikin but the fact that is Enumerable does not mean that is only a Collection since string is also Enumerable and returns the characters one by one...

So i suggest using

if (typeof(ICollection<>).IsAssignableFrom(pi.PropertyType))

answered Mar 15 '13 at 11:49

sstauross

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You are right about the string of course, but your solution fails (try it with List()). See my update for the code I wound up using. Cheers! – Berryl Mar 16 '13 at 12:18
1

This fails because no constructed type (like `List`) can be assigned to a generic type ( `ICollection<>`) (in fact, you can't declare a variable of type `ICollection<>`). So better use `typeof(ICollection)` (as suggested by the editor), which will also make it work for non-generic collections. – René Vogt Sep 19 '17 at 12:45
Very much indeed – Joanvo Jan 15 '18 at 11:18

score 8 · Answer 3 · edited Aug 09 '17 at 08:46

8

Try

private bool IsEnumerable(PropertyInfo pi)
{
   return pi.PropertyType.IsSubclassOf(typeof(IEnumerable));
}

edited Aug 09 '17 at 08:46

Jonas Stensved

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answered Aug 25 '10 at 20:12

Steve Danner

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I recently noticed that `x.IsSubClassOf(y)` will return false if x == y. In this situation, if the property happened to actually be of type `IEnumerable`, then the function would return false. – Dr. Wily's Apprentice Aug 25 '10 at 21:02
1

That is interesting, I've honestly never actually used this logic in this exact context, so I'm glad you pointed that out. Thanks. – Steve Danner Aug 26 '10 at 00:33

score 0 · Answer 4 · answered Jul 09 '22 at 07:43

You can also use "pattern matching". This works for both List<T> and IEnumerable<T>.

private void OutputPropertyValues(object obj)
{
    var properties = obj.GetType().GetProperties();

    foreach (var property in properties)
    {
        if (property.GetValue(obj, null) is ICollection items)
        {
            _output.WriteLine($"    {property.Name}:");

            foreach (var item in items)
            {
                _output.WriteLine($"        {item}");
            }
        }
        else
        {
            _output.WriteLine($"    {property.Name}: {property.GetValue(obj, null)}");
        }
    }
}

How to know if a PropertyInfo is a collection

UPDATE

4 Answers4

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