Can somone give example of Dependency Property in ViewModel

Question

Can somone give example of Dependency Property in ViewModel in WPF passed as datacontext to view. Will this require inheriting from DependencyObject? Lets say I want ListBox SelectedItem bound to a Dependency Property CurrentItem in ViewModel. I have it working from window object but same thing donnt work with ViewModel . In ViewModel I use GetProperty and SetProperty and not CLR property.

public partial class Window1 : Window
    {

        ObservableCollection<Person> persons;


        public ObservableCollection<Person> Persons
        {
            get
            {
                return persons;
            }

            set
            {
                persons = value;
            }
        }


        public static readonly DependencyProperty InfoTextProperty =
   DependencyProperty.Register(
      "InfoText",
      typeof(Person),
      typeof(Window1),
      new FrameworkPropertyMetadata(
         new PropertyChangedCallback(ChangeText)));

        public Window1()
        {
            InitializeComponent();
            this.DataContext = this;
            List<Person> people = new List<Person>();
            people.Add(new Person("Makeda Wilde"));
            people.Add(new Person(" Rosamaria Becnel"));
            people.Add(new Person("Jarrett Bernstein"));
            people.Add(new Person(" Leopoldo Palmer"));
            people.Add(new Person("Tyron Fisher"));
            people.Add(new Person(" Elba Kilpatrick"));
            people.Add(new Person("Ivory Lavender"));
            persons = new ObservableCollection<Person>(people);

            //persons.CollectionChanged += new System.Collections.Specialized.NotifyCollectionChangedEventHandler(persons_CollectionChanged);
        }

        void persons_CollectionChanged(object sender, System.Collections.Specialized.NotifyCollectionChangedEventArgs e)
        {

        }


        public ListBoxItem InfoText
        {
            get
            {
                return (ListBoxItem)GetValue(InfoTextProperty);
            }
            set
            {
                SetValue(InfoTextProperty, value);
            }
        }


        private static void ChangeText(DependencyObject source, DependencyPropertyChangedEventArgs e)
        {
            Person newPerson = (Person)e.NewValue;
            newPerson.IsSelected = true;

            Person oldPerson = (Person)e.OldValue;
            if (oldPerson != null)
            {
                oldPerson.IsSelected = false;
            }
        }







        //  #region INotifyPropertyChanged Members

        //  event PropertyChangedEventHandler PropertyChanged;
        //   // Create the OnPropertyChanged method to raise the event
        //protected void OnPropertyChanged(string name)
        //{
        //    PropertyChangedEventHandler handler = PropertyChanged;
        //    if (handler != null)
        //    {
        //        handler(this, new PropertyChangedEventArgs(name));
        //    }
        //}


        //  #endregion
    }


    public class Person : INotifyPropertyChanged
    {
        private bool isselected = false;
        public Person(string name)
        {
            this.Name = name;
            this.IsSelected = false;

        }
        public string Name { get; set; }
        public bool IsSelected
        {
            get
            {
                return isselected;
            }
            set
            {

                isselected = value;
                OnPropertyChanged("IsSelected");
            }
        }

        #region INotifyPropertyChanged Members

        public event PropertyChangedEventHandler PropertyChanged;
        // Create the OnPropertyChanged method to raise the event

        protected void OnPropertyChanged(string name)
        {
            PropertyChangedEventHandler handler = PropertyChanged;
            if (handler != null)
            {
                handler(this, new PropertyChangedEventArgs(name));
            }
        }
        #endregion


    }



<Grid>
        <ListBox Height="500"  Width="500" ItemsSource="{Binding Persons}"  Margin="104,46,212,0"  VerticalAlignment="Top"  SelectedItem="{Binding InfoText}"  >
            <ListBox.ItemTemplate>
                <DataTemplate>
                    <TextBlock Margin="2,2,2,2"  x:Name="tb" TextWrapping="Wrap" Text="{Binding Path=Name}"  />
                    <DataTemplate.Triggers>
                        <DataTrigger Binding="{Binding Path=IsSelected}" Value="true">
                            <Setter Property="Background"  TargetName="tb" Value="Red"/>
                        </DataTrigger>
                    </DataTemplate.Triggers>
                </DataTemplate>
            </ListBox.ItemTemplate>
        </ListBox>
    </Grid>

Answer 1

In order to define a DependencyProperty in your view model, your view model class must derive from DependencyObject. Otherwise the DependencyProperty won't work right.

Do you really need the property to be a DependencyPropety? Have you looked into implementing INotifyPropertyChanged instead?

Answer 2

Although you can implement a ViewModel as a DependencyObject with dependency properties, most people agree that it's better to use a POCO object implementing INotifyPropertyChanged... Have a look at this article by Kent Boogaart for a detailed comparison between the two approaches. There's also a SO question about this