WPF ICollectionView Filter Reset

Question

Hi!

I have a CollectionView from an ObservableCollection:

private static ObservableCollection<CalculationViewModel> _calculations;

CalculationViewModelsCollection = (CollectionView)CollectionViewSource.GetDefaultView(_calculations);

My problem is that, when the result of the filter is nothing, I'd like to clear the filter, and refilter with other conditions, but the collectionView is always empty. It is only if the filter's result is nothing.

I tried to reset the filter these ways:

CalculationViewModelsCollection.Filter = null;
CalculationViewModelsCollection.Refresh();

and

CalculationViewModelsCollection.Filter = delegate(object p)
{
 return true;
};

None of them worked :( .

Could you give some advice how to reset a filter on a CollectionView?

Thanks in advance!

Regards, Zoli

Answer 1

Hi there. From your example, I'm not entirely sure how you're getting your CollectionView, nor am I sure I understand your question correctly.

But anyway, I hope the sample code below helps you with your problem. It's an app that has a listbox containing strings, and a "filter" textbox. if nothing in the list matches the filter, the filter will be set to null and thus display all items.

XAML:

<Window x:Class="WpfApplication3.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:v="clr-namespace:WpfApplication3"
        Title="MainWindow" Height="350" Width="525">
    <StackPanel>
        <TextBox x:Name="textBox" TextChanged="TextBox_TextChanged"/>        
        <ListBox x:Name="listBox"/>
    </StackPanel>
</Window>

Code-behind:

public partial class MainWindow : Window
{
    ListCollectionView lcv;
    Predicate<object> filterFx;

    public MainWindow()
    {
        InitializeComponent();

        ObservableCollection<string> s = new ObservableCollection<string>();
        "The Quick Brown Fox Jumps Over The Lazy Dog"
            .Split(' ')
            .ToList()
            .ForEach((word) => s.Add(word.ToString()));

        this.lcv = new ListCollectionView(s);
        this.listBox.ItemsSource = this.lcv;

        this.filterFx = (p) => ((string)p).ToUpper().Contains(this.textBox.Text.ToUpper());
        lcv.Filter = this.filterFx;
    }

    private void TextBox_TextChanged(object sender, TextChangedEventArgs e)
    {
        lcv.Refresh();

        if (lcv.Count == 0)
            lcv.Filter = null;
        else
            lcv.Filter = filterFx;
    }
}

Answer 2

Hi!

Thanks the example!

Yes, with your code it works perfectly. I don't undestand what is wrong in my program.

I try to find out what I'm doing wrong, because in my program, if the result of the filter is nothing, and set Filter to null to see all item in the collection, the collectionview is empty again.

If I find the mistake I will write it here! I hope it will be soonly :) !

Answer 3

I did a big binding mistake. I don't understand how it works at all.

So the matter is that, it's simple to reset a filter, just set the value to null.

There is one more thing. I tried to create ListCollectionView like you did it.

this.lcv = new ListCollectionView(s);

But the filter didn't work, and I couldn't add SortDescription to the CollectionView.

I create CollectionView this way:

this.lcv = (CollectionView)CollectionViewSource.GetDefaultView(s);

and everything work fine. But ideally your technique have to work too.