How to call Count on a bunch of ISet properties where T varies

Question

I have a class with a bunch of properties of type ISet<T>, where T varies from property to property.

I'd like to iterate over an object's properties, find the ones that are some sort of ISet and call Count on each of them.

Thanks.

I guess you should start by [finding an object with the ISet Interface](https://stackoverflow.com/questions/1519530/using-reflection-to-find-interfaces-implemented) — Mong Zhu, Jul 24 '19 at 14:49
@MongZhu, I suppose I could check the class *names* for the substring "ISet", but an ISet isn't an ISet, so I don't think I can use *is* or *isAssignableFrom*. — Michael, Jul 24 '19 at 15:38
Do you want to call the `Count` property on the set, or do you just want to get the number of items in the set? — Sean, Jul 24 '19 at 16:06
@Sean, I needed the Count property, but I'm curious what you would have suggested had I simply needed the number of items... — Michael, Jul 28 '19 at 07:59
@Michael - I was just thinking that if you're just after the number of items then you can try and convert the property to an `IEnumerable — Sean, Jul 28 '19 at 14:08

Renat · Accepted Answer · 2019-07-24T15:52:06.320

This might work, obj is a target object:

Type targetType = obj.GetType();
foreach (var propertyInfo in targetType.GetProperties(BindingFlags.Instance | BindingFlags.Public | BindingFlags.FlattenHierarchy))
{
    var isetInterface = propertyInfo.PropertyType.IsGenericType && propertyInfo.PropertyType.GetGenericTypeDefinition() == typeof(ISet<>)
        ? propertyInfo.PropertyType
        : null;

    if(isetInterface == null)
    {
        isetInterface = propertyInfo.PropertyType
            .GetInterfaces()
            .FirstOrDefault(t => t.IsGenericType && t.GetGenericTypeDefinition() == typeof(ISet<>));
    }

    if (isetInterface != null)
    {
        object isetPropertyValue = propertyInfo.GetValue(obj);

        var countPropertyInfo = isetInterface
            .GetInterfaces()
            .First(t => t.IsGenericType && t.GetGenericTypeDefinition() == typeof(ICollection<>))
            .GetProperty("Count");

        if (isetPropertyValue == null)
        {
            Console.WriteLine($".{propertyInfo.Name} == null");
        }
        else
        {
            var count = countPropertyInfo.GetValue(isetPropertyValue);
            Console.WriteLine($".{propertyInfo.Name}.Count == {count}");
        }
    }
}

It works if the property is something like `HashSet`, but doesn't work if the property is already the interface `ISet`. You checked all the interfaces, but didn't check the property itself. e.g.: it won't handle this class: `public class Foo { public ISet bar {get; set;} }` — Wyck, Jul 24 '19 at 15:26

score 0 · Answer 2 · answered Aug 14 '19 at 06:08

@Renat's answer worked for me, but I tweaked it into something I found more convenient:

        public virtual string counts => typeof(Changeset)
        .GetProperties(BindingFlags.Instance | BindingFlags.Public | BindingFlags.FlattenHierarchy)
        .Where(prop => prop.GetValue(this) != null && count(prop) > 0)
        .Select(prop => $@".{prop.Name}.Count == {count(prop)}")
        .Join("\n");

    private int count(PropertyInfo prop)
    {
        var name = prop.Name;
        var isetInterface = prop.PropertyType.IsGenericType && prop.PropertyType.GetGenericTypeDefinition() == typeof(ISet<>)
            ? prop.PropertyType
            : null;

        if (isetInterface == null)
        {
            isetInterface = prop.PropertyType
                .GetInterfaces()
                .FirstOrDefault(t => t.IsGenericType && t.GetGenericTypeDefinition() == typeof(ISet<>));
        }

        if (isetInterface != null)
        {
            object isetPropertyValue = prop.GetValue(this);

            var countPropertyInfo = isetInterface
                .GetInterfaces()
                .First(t => t.IsGenericType && t.GetGenericTypeDefinition() == typeof(ICollection<>))
                .GetProperty("Count");

            if (isetPropertyValue == null)
                return 0;
            else
                return (int) countPropertyInfo.GetValue(isetPropertyValue);
        }

        return 0;
    }

Also, I found that if I can refer to the properties by name I can use

    private string count<T>(Func<Changeset, ISet<T>> selector)
    {
        var count = selector(this).Count;
        return count > 0 ? $"\n{typeof(T).Name}s:\t\t{count}" : "";
    }

as in

$"{count(x => x.prop)}"

How to call Count on a bunch of ISet properties where T varies

2 Answers2