CODEWITHSUNDEEP
c#wpfbinding
mike
mike

Reputation: 1744

How to extend a CollectionView's filter?

I have a class that represents a collection and implements, amongst others, the following interfaces:

So far, all is fine: I can bind a control, including sorting, filtering and even "live shaping".

First question: Due to the ICollectionViewFactory the IEnumerable.GetEnumerator is never called (by the UI), but it still appears to be required. Should I be smelling something here?

Then, I have one specific scenario where I want to do some additional filtering and the criteria will depend on the render context which is why I thought I'd use an IValueConverter with something like this:

public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
{
    var cv = (ICollectionViewFactory)value.CreateView();
    cv.ExtendFilter(i => i.AdditionalFilterProperty);

    return cv;
}

The ExtendFilter extension method looks like this:

public static void ExtendFilter(this ICollectionView view, Predicate<object> filter)
{
    if (view.Filter == null)
    {
        view.Filter = filter;
    }
    else
    {
        var originalFilter = view.Filter;
        view.Filter = item => originalFilter(item) && filter(item);
    }
}

Second question: Is there a better way to do this? I was thinking, maybe, expression trees...

Upvotes: 0

Views: 191

Answers (1)

Dean Chalk
Dean Chalk

Reputation: 20461

Firstly, it is correct that IEnumerable isnt called if your collection class implements ICollectionViewFactory. Deep in the WPF framework the ItemsSource (IEnumerable) has its default collection view created. In that code, if the collection already implements ICollectionViewFactory then it takes CreateView as the actual items source. If it doesnt implement it then it creates a default view with the IEnumerable as the items source.

Secondly, your composite filter logic seems reasonable. Expression trees take a lot more implementing, but would also provide a good solution also. Personally I would stick with what you have

Upvotes: 1

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