IList<> Property stays null even when member is instantiated

Question

I am having trouble using an IList property which always seems to return null, even though the member is is getting is instantiated:

    private List<ModelRootEntity> _validTargets = new List<ModelRootEntity>();

    public IList<IModelRootEntity> ValidTargets
    {
        get
        {
            return _validTargets as IList<IModelRootEntity>;
        }
        protected internal set
        {
            if (value == null)
                _validTargets.Clear();
            else
                _validTargets = value as List<ModelRootEntity>;
        }
    }

ModelRootEntity implements IModelRootEntity. I watched both values during debugging, whilst the member shows a positive count, the property stays null.

I also tried raising an exception within the property getter to throw if the counts of _validTargets and _validTargets as List<ModelRootEntity> are different, but it never threw.

Found question [Dictionary properties are always null despite dictionaries being instantiated, which seems similar, however in my case this seems to happen regardless of serialization.

Any ideas?

Why dont you change it to `private List _validTargets = new List(new List());` — Nilesh, Sep 01 '13 at 06:46
SLaks, Nilesh, good question. Probably deserves its own thread. I am open to advice on this. The `ModelRootEntity` is used within the domain and many internal methods expect more members than `IModelRootEntity` declares (which are the ones exposed via DTO's outside the domain). So I either cast once inside the property or in every internal use. Figured, doing it once was cleaner. — Stefan de Kok, Sep 01 '13 at 12:01
@SLaks, Nilesh, decided to open this as a new question: http://stackoverflow.com/questions/18560845/exposing-a-listdomain-objects-via-an-ilistinterface — Stefan de Kok, Sep 01 '13 at 17:12

score 0 · Answer 1 · answered Sep 01 '13 at 03:47

0

If you set your property to any value that isn't a List<ModelRootEntity>, the as expression will return null and the property will become null.

answered Sep 01 '13 at 03:47

SLaks

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score 0 · Accepted Answer · edited May 23 '17 at 12:05

I found the answer, thanks to @Nilesh comment above.

Replacing:

private List<ModelRootEntity> _validTargets = new List<ModelRootEntity>();

with:

private List<IModelRootEntity> _validTargets = new List<ModelRootEntity>();

exposed the real issue. The second line will not compile. The following post explained why: C# newbie List<Interface> question

The only odd thing was the exception I tried to force which never threw, and "threw" me off.

IList<> Property stays null even when member is instantiated

2 Answers2