ICollectionView.Source returns null when trying to update the View's Filter.

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4.00/5 (1 vote)

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Hi,

I have created an ICollectionView:

C#

private ObervableCollection<Apples> MyCollection = new ObervableCollection<Apples>();
public ICollectionView View {get; private set; }

private void Init()
{
 CollectionViewSource Cvs = new CollectionViewSource();
 Cvs.Source = ObervableCollection;
 View.Source =  Cvs.View; 
}

private void UpdateFilter(string Color)
{
 using (View.DeferRefresh) // Not required
    {
      View.Filter = (o) = > {return ((Apple)(o)).Color = Color;}
    }
}

Code compile errors might exist here, I'm on another PC..

The problem is that when i click a checkbox from the UI to reapply the filter based on a string, when the code reaches the "View.Filter = ....." it throws a null reference exception(with no more Info BUT if you observe you can see that the property of the View "SourceCollection" is NULL).

The Thread Executing is the MAIN thread..
I also tried using Invoke or BeginInvoke from the Dispatcher but with no luck..

More info:
Checking\Unchecking the checkbox from the Ui updates the binded backing property ShowHide(Bool).
The ShowHide Calls the UpdateFilter(string X) and then the problem occurs..

Thanks in advance

Posted 4-Sep-12 5:03am

BeStelios

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BeStelios · Answer 1 · 2012-09-04T22:21:00

C#

 public class ViewModel
    {
        ObservableCollection<customer> CustomerList = new ObservableCollection<customer>();
        public ICollectionView BlueCustomersView { get; private set; }
        public ICollectionView BlackCustomersView { get; private set; }

        public ICollectionView RedCustomersView { get; private set; } //UnBound
        public ICollectionView CyanCustomersView { get; private set; } //UnBound
        public ICollectionView PinkCustomersView { get; private set; } //UnBound
        public ICollectionView OrangeCustomersView { get; private set; } //UnBound



        public ViewModel()
        {
            for (int i = 0; i < 10000; i++)
            {
                Customer Cust = new Customer();
                Cust.Name = i;
                Cust.Color = (i % 2 == 0) ? Brushes.AliceBlue : Brushes.Black;
                CustomerList.Add(Cust);
            }

            /****************************************************************************
             * Move this Outside of the function to make things work
             * *************************************************************************/
            CollectionViewSource CvBlue = new CollectionViewSource();
            CollectionViewSource CvBlack = new CollectionViewSource();

            CollectionViewSource CvRed = new CollectionViewSource(); //UnBound
            CollectionViewSource CvCyan = new CollectionViewSource(); //UnBound
            CollectionViewSource CvPink = new CollectionViewSource(); //UnBound
            CollectionViewSource CvOrange = new CollectionViewSource(); //UnBound
            /***************************************************************************/

            /************ Bound **************/
            CvBlue.Source = CustomerList;
            BlueCustomersView = CvBlue.View;

            CvBlack.Source = CustomerList;
            BlackCustomersView = CvBlack.View;
            /************ **************/


            /************ Un-Bound **************/
            CvRed.Source = CustomerList;
            RedCustomersView = CvRed.View;

            CvCyan.Source = CustomerList;
            CyanCustomersView = CvCyan.View;

            CvPink.Source = CustomerList;
            PinkCustomersView = CvPink.View;

            CvOrange.Source = CustomerList;
            OrangeCustomersView = CvOrange.View;
            /************ **************/
        }



        public void ApplyFiltering()
        {
            //Bound CollectionViews
            BlueCustomersView.Filter = (o) => { return ((Customer)o).Color == Brushes.AliceBlue; };
            BlackCustomersView.Filter = (o) => { return ((Customer)o).Color == Brushes.Black; };

            // Unbound CollectionViews
            RedCustomersView.Filter = (o) => { return ((Customer)o).Color == Brushes.Red; };
            CyanCustomersView.Filter = (o) => { return ((Customer)o).Color == Brushes.Cyan; };
            PinkCustomersView.Filter = (o) => { return ((Customer)o).Color == Brushes.Pink; };
            OrangeCustomersView.Filter = (o) => { return ((Customer)o).Color == Brushes.Orange; };
        }
    }

</customer></customer>

In order to keep the Framework from disposing the CollectionViewSource you should make it a global class variable and not a variable inside a function.

If the Property View of the CollectionViewSource is binded somewhere or let's simple say that it has a reference things will work fine even if it's not global.

However once lost the Framework is probably GCing and dispocing it.
I suspect that either the Source Property of a CollectionView is a WeakReference
either the View Property of a CollectionViewSource.

Link of TestProject : https://docs.google.com/open?id=0B4xi5POVxsrxNDJnWnMxZ3p5VzA[^]

Kenneth Haugland · Answer 2 · 2012-09-04T06:22:00

Solution 1

See here:
http://marlongrech.wordpress.com/2008/11/22/icollectionview-explained/[^]

I think your problem is how you populate you ICollectionView, it should be done like this:

C#

ICollectionView view = CollectionViewSource.GetDefaultView(myData);

Posted 4-Sep-12 6:22am

Kenneth Haugland

Comments

BeStelios 4-Sep-12 13:54pm

No this is not the case..
I don't want to get the Default View, i need to get about 4 Filtered Views from 1 ObservableCollection and this is the exact way i should be getting them as instructed by msdn.

Kenneth Haugland 4-Sep-12 15:05pm

Sorry, you could just make a predicate that takes more than one filter string then. I view the ICollection class as a class that is meant to sit between the UI and the code behind. You could see how a former microsoft employee describes its uses simular to your problem here:
http://www.zagstudio.com/blog/454#.UEZXLSI3kso

BeStelios 5-Sep-12 4:06am

Thanks for your help,
I did read the article yesterday before posting here.
However i didn't wanted to change my implementation by filtering the CollectionViewSource.

Anyway the problem lies elsewhere, I have found the solution and going to post it in a sec.

Thanks for your time