强制转换为ObservableCollection

Question

I have an ObservableCollection of an object in C#. This object implements an interface. I would like to be able to convert the ObservableCollection of the object to an ObservableCollection of the interface without having to parse through the collection.

So for example:

I have an object "Guitar" which implements an interface called "IMusicalInstrument". I bind an ObservableCollection of Guitar objects to MyListBox. I want the following line of code to be able to convert listbox itemsSource to an ObservableCollection.

    ObservableCollection<IMusicalInstrument> InstrumentList = 
(ObservableCollection<IMusicalInstrument>)MyListBox.ItemsSource;

Currently, that is giving me an InvalidCastException.

Is there a way to accomplish this (without having to parse through the collection)?

Thanks, Seth

Answer 1

You can not cast it however one approach is to wrap your iteration which I know you want to avoid but unfortunately can't into an extension method .

public static class CollectionExtensions
{
    public static ObservableCollection<T> ToObservableCollection<T>(this IEnumerable<T> enumerableList)
    {
        if (enumerableList != null)
        {
            //create an emtpy observable collection object
            var observableCollection = new ObservableCollection<T>();

            //loop through all the records and add to observable collection object
            foreach (var item in enumerableList)
                observableCollection.Add(item);

            //return the populated observable collection
            return observableCollection;
        }
        return null;
    }
}

This would allow you to do something like...

ObservableCollection<IMusicalInstrument> InstrumentList = MyListBox.ItemsSource.ToObservableCollection<IMusicalInstrument>();

...which is what I believe you are after.

You can also simply pass the IEnumerable<T> reference into the constructor of ObservableCollection<T> ...

ObservableCollection<IMusicalInstrument> InstrumentList = new ObservableCollection<IMusicalInstrument>(MyListBox.ItemsSource);

Answer 2

除非MyListBox.ItemsSource是ObservableCollection<IMusicalInstrument>的实例，否则否，您不能进行ObservableCollection<IMusicalInstrument> 。

Answer 3

抱歉，您不能执行此操作，因为ObservableCollection<Guitar>不能被视为ObservableCollection<IMusicalInstrument> -例如，您不能在其上调用collection.Add(new Flute()) 。

Answer 4

如果只想管理集合中的项目，则可以尝试将ItemsSource强制转换为非通用IList。

Answer 5

If you are using ObservableCollection simply to handle collection changed events, you could cast to INotifyCollectionChanged and add your event handler. The INotifyCollectionChanged does not use generics, so you would have to cast in your event handler anyhow.

However, if you want to enumerate your collection of IMusicalInstrument instances, you can use the Linq Cast() extension method. eg

IEnumerable<IMusicalInstrument> instruments = 
     ((IEnumerable)MyListBox.ItemsSource).Cast<IMusicalInstrument>();

Hope that helps!