How can I make a read-only ObservableCollection property?
I don't like using ReadOnlyObservableCollection<T>
as it seems like a mistake / broken class; I prefer a contract based approach instead.
Here is what I use that allows for covarience:
public interface INotifyCollection<T>
: ICollection<T>,
INotifyCollectionChanged
{}
public interface IReadOnlyNotifyCollection<out T>
: IReadOnlyCollection<T>,
INotifyCollectionChanged
{}
public class NotifyCollection<T>
: ObservableCollection<T>,
INotifyCollection<T>,
IReadOnlyNotifyCollection<T>
{}
public class Program
{
private static void Main(string[] args)
{
var full = new NotifyCollection<string>();
var readOnlyAccess = (IReadOnlyCollection<string>) full;
var readOnlyNotifyOfChange = (IReadOnlyNotifyCollection<string>) full;
//Covarience
var readOnlyListWithChanges =
new List<IReadOnlyNotifyCollection<object>>()
{
new NotifyCollection<object>(),
new NotifyCollection<string>(),
};
}
}
The [previously] accepted answer will actually return a different ReadOnlyObservableCollection every time ReadOnlyFoo is accessed. This is wasteful and can lead to subtle bugs.
A preferable solution is:
public class Source
{
Source()
{
m_collection = new ObservableCollection<int>();
m_collectionReadOnly = new ReadOnlyObservableCollection<int>(m_collection);
}
public ReadOnlyObservableCollection<int> Items
{
get { return m_collectionReadOnly; }
}
readonly ObservableCollection<int> m_collection;
readonly ReadOnlyObservableCollection<int> m_collectionReadOnly;
}
See ReadOnlyObservableCollection anti-pattern for a full discussion.