ListView not updating on the itemsource ObservableCollection Item Property change

Question

Consider the following Sample Code :

View.xml

<Grid>
    <ListView Name="NameList" HorizontalAlignment="Left" Height="142" Margin="55,45,0,0" VerticalAlignment="Top" Width="389">
        <ListView.ItemTemplate>
            <DataTemplate>
                <Grid>
                    <Grid.ColumnDefinitions>
                        <ColumnDefinition Width="Auto"/>
                        <ColumnDefinition Width="Auto"/>
                    </Grid.ColumnDefinitions>
                    <Label Content="{Binding FirstName}"/>
                    <Label Content="{Binding LastName}" Grid.Column="1"/>
                </Grid>
            </DataTemplate>
        </ListView.ItemTemplate>
    </ListView>
    <Button Content="Button" HorizontalAlignment="Left" Margin="120,256,0,0" VerticalAlignment="Top" Width="75" Click="Button_Click"/>

</Grid>

View.xml.cs

public partial class MainWindow : Window
{
    ViewModel vm;
    public MainWindow()
    {
        InitializeComponent();
        vm = new ViewModel();
        this.DataContext = vm;
        NameList.ItemsSource = vm.fn;
    }

    private void Button_Click(object sender, RoutedEventArgs e)
    {
        vm.fn.Add(new fullname("P", "Q"));
        vm.fn[0].FirstName = "NewName";
    }

}

ViewModel.cs

class ViewModel : INotifyPropertyChanged
{

    public ViewModel()
    {
        fn = new ObservableCollection<fullname>();
        fn.CollectionChanged += ContentCollectionChanged;
        fn.Add(new fullname("A", "B"));
        fn.Add(new fullname("C", "D"));
    }

    public void ContentCollectionChanged(object sender, NotifyCollectionChangedEventArgs e)
    {
        if (e.Action == NotifyCollectionChangedAction.Remove)
        {
            foreach (fullname item in e.OldItems)
            {
                //Removed items
                item.PropertyChanged -= EntityViewModelPropertyChanged;
            }
        }
        else if (e.Action == NotifyCollectionChangedAction.Add)
        {
            foreach (fullname item in e.NewItems)
            {
                //Added items
                item.PropertyChanged += EntityViewModelPropertyChanged;
            }
        }
    }

    public void EntityViewModelPropertyChanged(object sender, PropertyChangedEventArgs e)
    {
        //This will get called when the property of an object inside the collection changes
    }

    public ObservableCollection<fullname> _fn;
    public ObservableCollection<fullname> fn
    {
        get { return _fn; }
        set { _fn = value; OnPropertyChanged("fn"); }
    }

    public event PropertyChangedEventHandler PropertyChanged;
    protected void OnPropertyChanged(string name)
    {
        PropertyChangedEventHandler handler = PropertyChanged;
        if (handler != null)
        {

        }
    }
}

Model.cs

class fullname : INotifyPropertyChanged
{
    public fullname(string f, string l)
    {
        FirstName = f;
        LastName = l;
    }

    public string _FirstName;
    public string FirstName
    {
        get { return _FirstName; }
        set { _FirstName = value; OnPropertyChanged("FirstName"); }
    }


    public string _LastName;
    public string LastName
    {
        get { return _LastName; }
        set { _LastName = value; OnPropertyChanged("LastName"); }
    }

    public event PropertyChangedEventHandler PropertyChanged;
    protected void OnPropertyChanged(string name)
    {
        PropertyChangedEventHandler handler = PropertyChanged;
        if (handler != null)
        {

        }
    }
}

If I add or remove any items in the ObservableCollection it updates the ListView in the View correctly but the problem is that if i modify the ObservableCollection item property the ListView is not updated.

for ex: On click of above specified button it
a. Adds a new item (Successfully reflected in the ListView)
b. Modify FirstName of first item (Not reflected in the ListView)

What should i do so as to make the modifications reflect in View.

I would be very thankful if anyone could point out what i am doing wrong.

Answer 1

ObservableCollection event are not fired when an item is changed, only when it is added, removed or moved. You must implement INotifyPropertyChanged interface in item class, and register each item event in collection.

See here

If you make heavy changes in the collection, you can raise a

NotifyCollectionChangedAction.Reset

event to reset them all

See here