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A Dictionary containing dictionaries with ObservableCollection values that have different entity types

I'm trying to implement a class in a Silverlight 4 RIA Services application that manages different ObservableCollections that are used for data binding. These ObservableCollections need to be identified by a string name and an integer classID, which I have implemented by nesting Dictionary objects in a Dictionary> object. The problem is, if I have explicit Entity types (which I do), this structure does not seem to work. The problem seems to occur when I am trying to put an ObservableCollection into an ObservableCollection (my guess as to how a generic entity list would be implemented).

For example:

  this.rawData = new Dictionary<int, ObservableCollection<DataRaw>>();
  this.constData = new Dictionary<int, ObservableCollection<SystemConstant>>();

  this.masterData = new Dictionary<string, Dictionary<int, ObservableCollection<Entity>>>();

  masterData.Add("test", raw开发者_开发百科Data);  <--- ERROR OCCURS HERE, 'best overloaded method has invalid arguments'

Note that I have tried using 'Object' instead of 'Entity' in the instantiation of masterData, but that did not solve the problem (it was admittedly a feeble attempt).

Thanks in advance for your insights. If there is a much better pattern I could be implementing here, I am open to being flexible. I mainly want to avoid having to code a bunch of Entity-type specific logic to manage the updating of this class. It seems like this should be generalizable.

Alex


For this to work you will have to declare RawData using the parent type, like this:

 this.rawData = new Dictionary<int, ObservableCollection<Entity>>();

Even if this dictionary will only hold instances of DataRaw, and even if DataRaw is derived from Entity, it is not possible to make an implicit conversion between ObservableCollection<DataRaw> and ObservableCollection<Entity>. For a moment I hesitated on whether C# would be able to solve this using variance, but after a quick proof of concept it was clear it cannot:

        var dataRaw = new DataRaw();
        Entity testEntity = dataRaw;

        var entityObservable = new ObservableCollection<Entity>();

        entityObservable.Add(dataRaw); // This is OK

        var dataRawObservable = new ObservableCollection<DataRaw>();
        dataRawObservable.Add(dataRaw); // This is fine too.

        entityObservable = dataRawObservable; // This is not valid

        var metaDictionary = new Dictionary<Int32, ObservableCollection<Entity>>();

        metaDictionary.Add(1, dataRawObservable); // This isn't valid either.

        metaDictionary.Add(2, entityObservable); // This is valid.
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