Bind ListView to ObservableCollection and Linq

Question

Hi Im trying to bind a ListView to a Linq, and make it react on changes in the collection.

public partial class MainWindow
{
    readonly ObservableCollection<Person> _persons = new ObservableCollection<Person>();
    readonly Team _team1 = new Team { Name = "Team 1" };
    readonly Team _team2 = new Team { Name = "Team 2" };
    readonly Team _team3 = new Team { Name = "Team 3" };

    public MainWindow()
    {
        InitializeComponent();

        _persons.Add(new Person {Name = "James", Team = _team1});
        _persons.Add(new Person {Name = "John", Team = _team2});
        _persons.Add(new Person {Name = "Peter", Team = _team3});
        _persons.Add(new Person {Name = "Jack", Team = _team1});
        _persons.Add(new Person {Name = "Jones", Team = _team2});
        _persons.Add(new Person {Name = "Bauer", Team = _team3});
        _persons.Add(new Person {Name = "Bo", Team = _team1});
        _persons.Add(new Person {Name = "Ben", Team = _team2});
        _persons.Add(new Person {Name = "Henry", Team = _team3});

        TeamList1.ItemsSource = from person in _persons where person.Team == _team1 select person;
        TeamList2.ItemsSource = from person in _persons where person.Team == _team2 select person;
        TeamList3.ItemsSource = from person in _persons where person.Team == _team3 select person;
    }

    private void ButtonClick(object sender, RoutedEventArgs e)
    {
        _persons[0].Team = _team2;
    }
}

And my Models

 public class Person : INotifyPropertyChanged
    {
        private string _name;
        public String Name
        {
            get { return _name; }
            set { _name = value; NotifyPropertyChanged("Name"); }
        }

        private Team _team;
        public Team Team
        {
            get { return _team; }
            set { _team = value; NotifyPropertyChanged("Team"); }
        }

        public override string ToString()
        {
            return string.Format("Name {0}\t{1}", Name, Team);
        }
        public event PropertyChangedEventHandler PropertyChanged;

        private void NotifyPropertyChanged(String info)
        {
            if (PropertyChanged != null)
            {
                PropertyChanged(this, new PropertyChangedEventArgs(info));
            }
        }
    }

    public class Team : INotifyPropertyChanged
    {
        private string _name;
        public string Name
        {
            get { return _name; }
            set { _name = value; NotifyPropertyChanged("Name"); }
        }

        public override string ToString()
        {
            return Name;
        }
        public event PropertyChangedEventHandler PropertyChanged;

        private void NotifyPropertyChanged(String info)
        {
            if (PropertyChanged != null)
            {
                PropertyChanged(this, new PropertyChangedEventArgs(info));
            }
        }
    }

And the Xaml

<Grid>
        <StackPanel Orientation="Vertical">
        <StackPanel>
            <ListView Name="TeamList1"/>
            <ListView Name="TeamList2"/>
            <ListView Name="TeamList3"/>
        </StackPanel>
            <Button Content="Click Me" Click="ButtonClick"/>
        </StackPanel>
    </Grid>

When the ButtonClick is called I would like my ListView to reflect the changes it made on the _persons.

Answer 1

Just don't use linq, there are CollectionViews for this sort of thing which have filters, you then only have to refresh the views (See: How to: Filter data in a view ). (If you must use linq there are also bindable extensions to it)

Answer 2

The LINQ query is evaluated when it is bound to the data source and the items in the list view are generated. The LINQ query will not be re-evaluated whenever you change the properties of a person inside the original list _persons . To achieve this, you have to do a custom implementation that listens to the PropertyChanged event of each Person in the original list and updates an ObservableCollection<Person> accordingly. This observable collection you would bind to the list view.

Answer 3

You need my ObservableComputations library. Using this library you can code like this:

    TeamList1.ItemsSource = _persons.Filtering(person.Team == _team1);
    TeamList2.ItemsSource = _persons.Filtering(person.Team == _team2);
    TeamList3.ItemsSource = _persons.Filtering(person.Team == _team3);