How to access the internal filtered collection of ICollectionView?

Question

I've these collection and collectionviews:

public ICollectionView Tenants { get; set; }
public ICollectionView Plots { get; set; }
List<int> foundPlots

and these subscription and filters:

Tenants.CurrentChanged += onTenantChanged;
Plots.CurrentChanged += onPlotChanged;
Plots.Filter = filterPlots;

I don't want to have duplicates in Plots so to keep track of plot that has passed the filter, I add PlotId of the lease in foundPlots. Whenever onTenantChanged is called, I clear the foundPlots:

void onTenantChanged(object sender, EventArgs e)
{
    foundPlots.Clear();
    selectedTenant = Tenants.CurrentItem as Tenant;
    Plots.Refresh();
    Plots.MoveCurrentToFirst();
}

and it resets the selectedPlot:

void onPlotChanged(object sender, EventArgs e)
{
    selectedPlot = Plots.CurrentItem as Lease;
    ...
}

and in filterPlots method I've these:

bool filterPlots(object o)
{
    if (selectedTenant == null) return false;
    var lease = (o as Lease);      
    if(selectedTenant.Id == lease.TenantId)
    {
        var contained = foundPlots.Contains(lease.PlotId);
        if (!contained) foundPlots.Add(lease.PlotId);
        return !contained;
    }
    return false;        
}

It works if I add a Lease object in the underlying collection Plots is pointing to and also works if I don't modify the underlying collection. If I, however, replace a lease or after modifying a property of a Lease in the collection, call RaiseCollectionChanged() on the underlying collection, filterPlots is invoked and it doesn't get the chance to clear the foundPlots and I get unexpected results!

Is there a way to access the internal filtered collection of Plots in filterPlots method to check which plots have passed the filter already as the filter progresses?

Answer 1

I have to set two properties to make it work. For example:

Spaces = new CollectionViewSource() 
{ 
    Source = MainVM.spaces, 
    IsLiveFilteringRequested = true, 
    LiveFilteringProperties = { "IsVacant"}
 }.View;

In addition to IsLiveFilteringRequested I've to have LiveFilteringProperties, with that it now works, as expected, when I add, replace or modify a property of a Lease.