Cleaning up automatically created View Model - wpf

Question

Currently I'm binding my View Control straight to my Model.
But I'd like to :
a) provide more events/properties than the ones exposed in the Model.
b) provide properties based on Model data that are more suited for the View
And so to do this, I've decided to introduce a layer in between, which I'm calling the ViewModel(not sure if this is the correct use for the term ViewModel)
The work of the ViewModel in my scenario is to subscribe to all the events exposed by the Model and use those events to modify dependency properties in the ViewModel.
I've done this as follows.
<ItemsControl ItemsSource="{Binding Items}">
<ItemsControl.ItemTemplate>
<DataTemplate>
<local:View DataContext="{Binding Converter={StaticResource modelToViewModel}}"/>
</DataTemplate>
</ItemsControl.ItemTemplate>
</ItemsControl>
Here, Items is a collection of 'Model' type data, which I convert to 'ViewModel' types that the view can then bind to.
public class Model : INotifyPropertyChanged
{
public event PropertyChangedEventHandler PropertyChanged;
int m_age;
public int Age
{
get { return m_age; }
set { m_age = value; NotifyPropertyChanged("Age"); }
}
void NotifyPropertyChanged(string _property)
{
if (PropertyChanged != null)
{
PropertyChanged(this, new PropertyChangedEventArgs(_property));
}
}
}
public class ViewModel : DependencyObject
{
public Model Model { get; private set; }
public ViewModel(Model _model)
{
Model = _model;
Model.PropertyChanged += OnModelPropertyChanged;
}
void OnModelPropertyChanged(object sender, PropertyChangedEventArgs e)
{
// .. here - I would modify this ViewModels dependency properties
}
}
public class ModelToViewModel : IValueConverter
{
public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
{
return new ViewModel(value as Model);
}
public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture)
{
throw new NotImplementedException();
}
}
The problem I have now, is how to dispose of the ViewModel so it can unregister the property changed events in ViewModel. I'm thinking the best place to do this would be in the unloaded event of the View, but would like your thoughts.
public partial class View : UserControl
{
public View()
{
Unloaded += OnUnloaded;
InitializeComponent();
}
void OnUnloaded(object sender, RoutedEventArgs e)
{
if (DataContext != null)
{
(DataContext as ViewModel).Dispose();
}
}
}
Edit : I guess I would also need to Call dispose when the datacontext of the View changes, which would occur if an Item in the Items list was replaced.

Answer 1

Well you could implement IDisposible.
public class ViewModel : DependencyObject, IDisposable
{
public Model Model { get; private set; }
public ViewModel(Model _model)
{
Model = _model;
Model.PropertyChanged += OnModelPropertyChanged;
}
~ViewModel()
{
Dispose(false);
}
void OnModelPropertyChanged(object sender, PropertyChangedEventArgs e)
{
// .. here - I would modify this ViewModels dependency properties
}
public void Dispose()
{
Dispose(true);
GC.SupressFinalize();
}
protected virtual void Dispose(bool disposing)
{
if (disposing)
{
if (Model != null)
Model.PropertyChanged -= OnModelPropertyChanged;
}
}
}
If you're wondering about the implementation. You can find some information here. You must also unassign the call back in the view.
public partial class View : UserControl
{
public View()
{
Unloaded += OnUnloaded;
InitializeComponent();
}
void OnUnloaded(object sender, RoutedEventArgs e)
{
if (DataContext != null)
{
(DataContext as ViewModel).Dispose();
}
Unloaded -= OnUnloaded; // <---
}
}