与接口的协方差-接口的枚举

Question

I have a class like this:

public partial class GmxGlobalList : DynamicBindingListBase<GmxGlobal> 

Where DynamicBindingListBase implements Collection<T> which extends from IEnumerable<T> - in this case IEnumerable<GmxGlobal> .

The class GmxGlobal is defines like

public partial class GmxGlobal : IGmxGlobal 

I want now to declare GmxGlobalList like

public partial class GmxGlobalList : DynamicBindingListBase<GmxGlobal>, IEnumerable<IGmxGlobal>

But this does not work, because I should declare the Method IEnumerator<IGmxGlobal> GetEnumerator() - but this is already implemented from Collection<T> - but not with IGmxGlobal but with GmxGlobal . I would ask you, why I have to implement IEnumerator<IGmxGlobal> GetEnumerator() ? - What sould I do, that I can declare, that GmxGlobalList is an IEnumerable or ICollection or IList of IGmxGlobal (or something other where IGmxGlobal can be enumerated).

Answer 1

Since DynamicBindingListBase<T> implements IEnumerable<T> and GmxGlobalList inherits from DynamicBindingListBase<GmxGlobal> and implements IEnumerable<IGmxGlobal> .
GmxGlobalList implements both IEnumerable<GmxGlobal> and IEnumerable<IGmxGlobal> .

I'm going to assume that DynamicBindingListBase<T> already has a concrete implementation of IEnumerable<T> . This implementation wouldn't work as a IEnumerable<IGmxGlobal> since IEnumerable<IGmxGlobal> has a wider scope than IEnumerable<GmxGlobal> .

If you were to just have the following:

GmxGlobalList : DynamicBindingListBase<GmxGlobal>

Due to IEnumerable being co-variant, you can already use GmxGlobalList as a IEnumerable<IGmxGlobal> . Like this:

IEnumerable<IGmxGlobal> foo = new GmxGlobalList();

If you really need to implement IEnumerable<IGmxGlobal> you can write the implementation details to wrap around DynamicBindingListBase<GmxGlobal> .

public IEnumerator<IGmxGlobal> GetEnumerator()
{
    return (base as IEnumerator<GmxGlobal>).GetEnumerator();
}

IEnumerator IEnumerable.GetEnumerator()
{
    return GetEnumerator();
}

Answer 2

这样行吗？

IEnumerable<IGmxGlobal> e = (IEnumerable<GmxGlobal>)instanceOfGmxGlobalList;