Argthtjtr

WPF C# How can I filter a ObservableCollection or QueryableCollectionView?

I want to filter and list all categories which has the same duplicated Category Code.

Like code: Test123 consists of these categories. In other word, the categorycode should be unique.

I tried this with QueryableCollectionView:

var test = CategoryCollection.GroupBy(Category => Category.Code).Where(w => w.Count() > 1);

But it didn't work.

My code sample:

    public ObservableCollection<Category> GetCategory

    {

        get

        {

            this._getCategory = GetCategory();

            this._getCategory.GroupBy(category => category.Code).ToList().Where(w => w.Count() > 1); ;

            this._getCategory = new ObservableCollection<Category>(_getCategory);

            return this._getCategory.               

        }

        set

        {

            if (this._getCategory != value)

            {

                this._getCategory = value;

                this.OnPropertyChanged("GetCategory");

            }

        }

    }

I've made a code sample that works as you've described now, see below:

MainWindow.xaml

<Window x:Class="TestWpfApplication.MainWindowView"

    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"

    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"

    xmlns:d="http://schemas.microsoft.com/expression/blend/2008"

    xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"

    mc:Ignorable="d"

    Title="MainWindow" 

    Height="450" 

    Width="800">



<Grid>

    <Grid.ColumnDefinitions>

        <ColumnDefinition/>

        <ColumnDefinition/>

    </Grid.ColumnDefinitions>

    <Grid.RowDefinitions>

        <RowDefinition />

        <RowDefinition />

    </Grid.RowDefinitions>



    <ListBox Grid.Row="0" Grid.Column="0" Name="CategoryListBox" ItemsSource="{Binding Path=CategoryCollection}" DisplayMemberPath="Description" />

    <TextBox Grid.Row="0" Grid.Column="1" Text="{Binding ElementName=CategoryListBox, Path=SelectedItem.Code}" />

</Grid>

MainWindow.xaml.cs

using System.Windows;



namespace TestWpfApplication

{

    public partial class MainWindowView : Window

    {

        private readonly MainWindowViewModel _mainWindowViewModel = new MainWindowViewModel();



        public MainWindowView()

        {

            InitializeComponent();



            DataContext = _mainWindowViewModel;

        }

    }

}

MainWindowViewModel.cs

using System;

using System.Collections.Generic;

using System.ComponentModel;

using System.Linq;

using System.Windows.Data;



namespace TestWpfApplication

{

    internal class MainWindowViewModel

    {

        private readonly List<Category> _categories;



        public MainWindowViewModel()

        {

            _categories = new List<Category>

            {

                new Category {Code = 1, Description = "Blah"},

                new Category {Code = 1, Description = "Blah"},

                new Category {Code = 2, Description = "Pop"},

                new Category {Code = 3, Description = "No"},

                new Category {Code = 3, Description = "No"},

                new Category {Code = 4, Description = "Yes"}

            };



            HookUpCategoryEvents();



            CategoryCollection = CollectionViewSource.GetDefaultView(_categories);

            CategoryCollection.Filter = OnlyShowIfMoreThanOne;

        }



        private bool OnlyShowIfMoreThanOne(object obj)

        {

             Category item = obj as Category;



             return _categories.Count(c => c.Code == item.Code) > 1;

        }



        public ICollectionView CategoryCollection { get; }



        private void HookUpCategoryEvents()

        {

            // If you add items or remove them at any point then you need to call this method

            // It removes the event so you don't get existing items being 'hooked up' double or more times



            foreach (var category in _categories)

            {

                category.CodeChanged -= CategoryOnCodeChanged;

                category.CodeChanged += CategoryOnCodeChanged;

            }

         }



        private void CategoryOnCodeChanged(object sender, EventArgs e)

        {

            CategoryCollection.Refresh();

        }

    }

}

Category.cs

using System;



namespace TestWpfApplication

{

    public class Category

    {

        private int _code;

        private string _description;



        public event EventHandler CodeChanged;



        public int Code

        {

            get => _code;

            set

            {

                if (_code != value)

                {

                    _code = value;

                    OnCodeChanged();

                }

            }

        }



        public string Description

        {

            get => _description;

            set => _description = value;

        }



        private void OnCodeChanged()

        {

            CodeChanged?.Invoke(this, EventArgs.Empty);

        }

    }

}

This displays a simple ListBox that is set to show the Description property of the Category class and a TextBox that shows the SelectedItem.Code of the ListBox.
In the ViewModel the ICollectionView has a filter applied to it so that it only shows items those codes appear more than once. An event is fired from the Category class upon setting the Code property (from the TextBox) which the MainWindowViewModel listens to and uses to call .Refresh() on the ICollectionView. There is no validation or other things that you'd want in production code but this should show you the basics of what you're wanting.

var test = CategoryCollection.GroupBy(Category => Category.Code).toList().Where(w => w.Count() > 1);

List<Category> listResult= yourObservableCollection.GroupBy(c => c.Code)

.Select(cl=>new Caegory

{

    Code=cl.First().Code;

    // other parameters of Category here

}).ToList().Where(w=>w.Count()>1);

ObservableCollection<Category> result=new ObservableCollection<Category>(listResult);

I don't know about QueryableCollectionView, but for ObservableCollection it works