Question

I have a couple of complex objects that I’d like to compare properties on. The following code does a fine job, up until you get to a collection. I’d like to recursively call the function with each member of the collection. Can someone take a look and help me to determine the type of object in the collection so that I can call HasPropertyChanged again?

This pseudocode shows my intent

      if (p.GetType() == typeof(System.Collections.Generic.List<>))
       {
            foreach (var blah in //the list)
            {
                HasPropertyChanged<//TheType>(Type obj1, Type obj2, null);
            }
        }

Also, this part of the code bugs me. If I don’t call the tostring method, I’ll get some funky results, like id 63633 not equaling 63633

    object val1 = Original.GetType().GetProperty(p.Name).GetValue(Original, null);
        object val2 = Modified.GetType().GetProperty(p.Name).GetValue(Modified, null);
        if (!IgnoreProperties.Contains(p.Name) && 
            val1 != null && val2 != null && 
            val1.ToString() != val2.ToString())
        {
            return true;
        }

Here it is in it’s entirety.

private bool HasPropertyChanged<T>(T Original, T Modified, string[] IgnoreProperties)
    {
        if (Original == null || Modified == null)
            return false;
        if (IgnoreProperties == null)
            IgnoreProperties = new string[] { };

        IEnumerable<PropertyInfo> properties = typeof(T).GetProperties();

        foreach (var p in properties)
        {
            if (p.GetType() == typeof(System.Collections.Generic.List<>))
            {
                foreach (var blah in //the list)
                {
                    HasPropertyChanged<//TheType>(Type obj1, Type obj2, null);
                }
            }
            object val1 = Original.GetType().GetProperty(p.Name).GetValue(Original, null);
            object val2 = Modified.GetType().GetProperty(p.Name).GetValue(Modified, null);
            if (!IgnoreProperties.Contains(p.Name) && 
                val1 != null && val2 != null && 
                val1.ToString() != val2.ToString())
            {
                return true;
            }
        }
        return false;
    }

Answer 1

Since you’re dealing with types at runtime, you should have a non-generic version of your function which takes a Type parameter:

private bool HasPropertyChanged<T>(T Original, T Modified, string[] IgnoreProperties)
{
    return HasPropertyChanged(typeof(T), Original, Modified, IgnoreProperties);
}

private bool HasPropertyChanged(Type T, object Original, object Modified, string[] IgnoreProperties)
{
    // ...
}

With that, you can call the method for the list elements:

if (p.PropertyType.IsGenericType && p.PropertyType.GetGenericTypeDefinition() == typeof(System.Collections.Generic.List<>))
{
    object val1 = p.GetValue(Original, null);
    object val2 = p.GetValue(Modified, null);

    // First check count...
    PropertyInfo countProperty = p.PropertyType.GetProperty("Count");
    int count1 = countProperty.GetValue(val1, null);
    int count2 = countProperty.GetValue(val2, null);
    if (count1 != count2) return true;

    // Now iterate:
    var enumerator1 = (val1 as System.Collections.IEnumerable).GetEnumerator();
    var enumerator2 = (val2 as System.Collections.IEnumerable).GetEnumerator();
    while (enumerator1.MoveNext())
    {
        enumerator2.MoveNext();
        // check for null, skipping here...
        object elem1 = enumerator1.Current;
        object elem2 = enumerator2.Current;
        if (HasPropertyChanged(elem1.GetType(), elem1, elem2, IgnoreProperties)) return true;
    }
}
// ...