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IList <T>, IEnumerable <T> and ObservableCollection <T>

I have two classes defined as

public class PostleitzahlList : ObservableCollection<Postleitzahl> {
}

public class Postleitzahl : IPostleitzahl {
}

Now I have a Service-Class that contains

PostleitzahlList _postleitzahlList;

This Serviceclass must also implement the Service-Interface Property, which returns _postleitzahlList, but this interface only knows IPostleitzahl- it does not know PostleitzahlListor Postleitzahl. this property should be used for binding in WPF.

I am trying to declare and implement this property. I tried

    public ObservableCollection<IPostleitzahl> PostleitzahlList {
        get { return this._postleitzahlList; }
    }

and

    public IList<IPostleitzahl> PostleitzahlList {
        get { return this._postleitzahlList; }
    }

But both do not work. It looks like the work looks like:

    public IEnumerable<IPostleitzahl> PostleitzahlList {
        get { return this._postleitzahlList; }
    }

I ask myself now 1. Why are the first and second attempts not working? 2. What is the best solution to solve this problem?

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2 answers

. ObservableCollection<Postleitzahl> ObservableCollection<IPostleitzahl>, . , :

ObservableCollection<string> strings = new ObservableCollection<string>();

// This is invalid, but it what you're trying to do, effectively.
ObservableCollection<object> objects = strings;

// This would have to work... it fine...
objects.Add(new object());

// And this should be fine too...
string x = strings[0];

... , , , , . -... , .

IEnumerable<T> T, - - :

// There nothing you can do to violate type safety here...
Observable<string> strings = new ObservableCollection<string>();
IEnumerable<object> objects = strings;

generics MSDN.

IPostleitzahl? ObservableCollection<Postleitzahl> IList<Postleitzahl>, . , ObservableCollection<IPostleitzahl> , Postleitzahl.

+5

PostleitzahlList

public class PostleitzahlList : ObservableCollection<IPostleitzahl> {
}

elementtype IPostleitzahl Postleitzahl?

. @jon skeet answer

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