How can I recursively search properties in C# only if those properties inherit from some base class?

Question

How can I recursively get all the properties of an object only if the type of the property inherits from some base class?

This was my attempt:

static IEnumerable<PropertyInfo> FindProperties(object objectTree, Type targetType)
{
    if (objectTree.GetType().IsAssignableFrom(targetType))
    {
        var properties = objectTree.GetType().GetProperties();
        foreach (var property in properties)
        {
            yield return property;
        }

        foreach (var property in FindProperties(properties, targetType))
        {
            yield return property;
        }
    }
}

So I could call,

var allPropertiesOfPageTypes = FindProperties(someClass, typeof(Page));

However, the number of properties returned is always zero. What am I doing wrong?

Edit:

I'm not sure if this matters but the subclasses are generic classes:

public abstract class MasterPage<T> : BasePage<T> where T : MasterPage<T>

That inherits:

public abstract class BasePage<T> : Page where T : BasePage<T>

Things that inherit from Master/BasePage seem to be returning false for IsAssignableFrom?

Answer 1

You need to only recurse when you have the right type, and you need an instance, not the property itself:

static IEnumerable<PropertyInfo> FindProperties(object objectTree, Type targetType)
{
    if (targetType.IsAssignableFrom(objectTree.GetType()))
    {
        var properties = objectTree.GetType().GetProperties();
        foreach (var property in properties)
        {
            yield return property;

            if (targetType.IsAssignableFrom(property.PropertyType))
            {
                object instance = property.GetValue(objectTree, null);
                foreach (var subproperty in FindProperties(instance, targetType))
                {
                    yield return subproperty;
                }
            }
        }
    }
}

Answer 2

In order to verify if an object inherits from another class you have to do the opposite of what you are doing:

 if (targetType.IsAssignableFrom(objectTree.GetType()))

this works in a similar way to:

Parent o = new Derived();

Answer 3

Maybe this could work?

public static LinkedPageElement<TElement> GetLinkedElement<TPage, TElement>(Page page, bool verbose = true) where TElement : class
{
    var propInfos = page.GetType().GetProperties();

    // First try to find the property in the current page type
    foreach (var propInfo in propInfos)
    {
        var attributes = propInfo.GetCustomAttributes(typeof(LinkedPageAttribute), true);
        if (attributes.Length == 0) continue;

        var linkedPageAttribute = (from a in attributes where a.GetType() == typeof(LinkedPageAttribute) select a).FirstOrDefault();
        if (linkedPageAttribute == null || !(linkedPageAttribute is LinkedPageAttribute)) continue;

        if ((linkedPageAttribute as LinkedPageAttribute).PageType == typeof(TPage))
        {
            return new LinkedPageElement<TElement>
            {
                Element = propInfo.GetValue(page, null) as TElement,
                AutoClick = (linkedPageAttribute as LinkedPageAttribute).AutoClick
            };
        }
    }

    // Then try to find it in a property
    var containedInProperty = propInfos.Where(x => x.PropertyType.IsSubclassOf(typeof(Page)))
        .Select(x => GetLinkedElement<TPage, TElement>((Page)x.GetValue(page, null), false))
        .FirstOrDefault(x => x != null);

    if (containedInProperty != null) return containedInProperty;

    // you are trying to navigate to a page which cannot be reached from the current page, check to see you have a link with LinkedPage attribute
    if (verbose)
        throw new ArgumentException("You don't have a link to this page {0} from this page {1}".FormatWith(typeof(TPage), page.GetType()));

    return null;
}