How do objects NOT implementing INPC notify changes?

Question

Simple question for those who know the answer:

I have a basic Person class defined as follows:

public class Person
{
   public Person(string name, string surname)
   {
        this.Name = name;
        this.Surname = surname;
   }

   public string Name { get; set; }

   public string Surname { get; set; }
}

a very simple ViewModel

public partial class SimpleViewModel : Screen
{
    public SimpleViewModel()
    {
        this.Persons = new ObservableCollection<Person>(this.GetPersons());
    }

    private ObservableCollection<Person> persons;
    public ObservableCollection<Person> Persons
    {
        get { return this.persons; }
        set
        {
            if (this.persons == value) return;

            this.persons = value;
            this.NotifyOfPropertyChange(() => this.Persons);
        }
    }


    private Person selectedPerson;
    public Person SelectedPerson
    {
        get { return this.selectedPerson; }
        set
        {
            if (this.selectedPerson == value) return;

            this.selectedPerson = value;
            this.NotifyOfPropertyChange(() => this.SelectedPerson);
        }
    }

    IEnumerable<Person> GetPersons()
    {
        return
            new Person[]
            {
                new Person("Casey", "Stoner"),
                new Person("Giacomo", "Agostini"),
                new Person("Troy", "Bayliss"),
                new Person("Valentino", "Rossi"),
                new Person("Mick", "Doohan"),
                new Person("Kevin", "Schwantz")
            };
    }
}

and a very simple View

<Window x:Class="Test.SimpleView"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        Title="SimpleView"
        Width="300"
        Height="300">
    <Grid>
        <Grid.RowDefinitions>
            <RowDefinition />
            <RowDefinition Height="8"/>
            <RowDefinition Height="Auto"/>
        </Grid.RowDefinitions>
        <Grid.ColumnDefinitions>
            <ColumnDefinition/>
        </Grid.ColumnDefinitions>

        <ListView x:Name="lsv"
                  ItemsSource="{Binding Persons}"
                  SelectedItem="{Binding SelectedPerson}" Grid.RowSpan="3">
            <ListView.View>
                <GridView>
                    <GridViewColumn DisplayMemberBinding="{Binding FirstName}" />
                    <GridViewColumn DisplayMemberBinding="{Binding LastName}" />
                </GridView>
            </ListView.View>
        </ListView>

        <StackPanel Grid.Row="2"
                    Grid.Column="1"
                    VerticalAlignment="Center">
            <TextBox Text="{Binding SelectedPerson.FirstName, UpdateSourceTrigger=PropertyChanged}" />
            <TextBox Text="{Binding SelectedPerson.LastName, UpdateSourceTrigger=PropertyChanged}" />
        </StackPanel>

    </Grid>
</Window>

if I edit FirstName or LastName in the textbox, the listview updates.

How is that possibile if Person doesn't implement INotifyPropertyChanged?

Thanks

P.S. ViewModel inherits Screen from Caliburn.Micro

Answer 1

This is using the PropertyDescriptor to propagate the change notifications as described here.

I wouldn't rely on this sort of binding.

• It is slower and heavier weight than implementing INPC (best practices suggestion for POCO objects).
• It only works for changes initiated through Binding syntax. If you were to programmatically change the value of Name, the list would not respond.

Answer 2

I am not sure but I think........

1. Your Persons property implements INotifyPropertyChanged interface and so, Indirectly all the objects or properties in your Person class also implements INotifyPropertyChanged.

2. I might be wrong in this case. ObservableCollection also implements INotifyPropertyChanged internally. So, there is no requirement to implement INotifyPropertyChanged in Persons Property.