For Silverlight or WPF when control is bound to Observable collection , and I am only interested in collection additions/deletions to be reflected in a control – i.e. one way binding – am I right in thinking that there is no need for INotifyPropertyChanged in a class the collection is comprised of. But changes to the existing element of collection won't be reflected in user interface in this case.
R – Observable collection without INotifyProperChanged for one way binding
observablecollectionsilverlightwpf
Related Solutions
Use an ItemsControl
and a DataTemplate
<ItemsControl ItemsSource="{Binding YourCollection}">
<ItemsControl.ItemTemplate>
<DataTemplate>
<uc:YourUserControl />
</DataTemplate>
</ItemsControl.ItemTemplate>
</ItemsControl>
Update 8/19
The concise answer is you have to implement INotifyPropertyChanged on the view model and notify listeners when the Property/Collection is changed.
Implement INotifyPropertyChanged on the ViewModel
* implement the interface INotifyPropertyChanged
* define the event (public event PropertyChangedEventHandler PropertyChanged)
* subscribe to the CollectionChanged event (Classnames.CollectionChanged += ...)
* fire the event for listeners
Best,
/jhd
ViewModel update per above... ValueConverter now called on all changes to the Property/Collection
public class ViewModel : INotifyPropertyChanged
{
private readonly ObservableCollection<string> _classnames = new ObservableCollection<string>();
public ViewModel()
{
Classnames.CollectionChanged += Classnames_CollectionChanged;
}
public event PropertyChangedEventHandler PropertyChanged;
private void Classnames_CollectionChanged(object sender, NotifyCollectionChangedEventArgs e)
{
NotifyPropertyChanged("Classnames");
}
private void NotifyPropertyChanged(string info)
{
PropertyChangedEventHandler handler = PropertyChanged;
if (handler != null)
{
foreach (PropertyChangedEventHandler d in handler.GetInvocationList())
{
d(this, new PropertyChangedEventArgs(info));
}
}
}
public ObservableCollection<string> Classnames
{
get { return _classnames; }
}
}
The XAML binding...
<UserControl.Resources>
<local:ViewModel x:Key="TheViewModel"/>
<local:TabConverter x:Key="TabConverter" />
</UserControl.Resources>
<StackPanel DataContext="{StaticResource TheViewModel}">
<ListBox ItemsSource="{Binding Classnames}" />
<controls:TabControl x:Name="TheTabControl"
ItemsSource="{Binding Classnames, Converter={StaticResource TabConverter}, ConverterParameter={StaticResource TheViewModel}}"/>
<Button Click="Button_Click" Content="Change Classnames" />
</StackPanel>
The ValueConverter (basically unchanged
public class TabConverter : IValueConverter
{
public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
{
var source = value as ObservableCollection<string>;
if (source == null)
return null;
//also sorted out the binding syntax to pass the ViewModel as a parameter
var viewModel = parameter as ViewModel;
if (viewModel == null)
throw new ArgumentException("ConverterParameter must be ViewModel (e.g. ConverterParameter={StaticResource TheViewModel}");
var tabItems = new List<TabItem>();
foreach (string classname in source)
{
// real code dynamically loads controls by name
var tabItem = new TabItem
{
Header = "Tab " + classname,
Content = new Button {Content = "Content " + classname}
};
tabItems.Add(tabItem);
}
return tabItems;
}
public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture)
{
throw new NotImplementedException();
}
}
Best Answer
If I understand you well, yes you can have items that don't implement
INotifyPropertyChanged
in anObservableCollection
. Any list control bound to the collection will be correctly updated in terms of items added/removed, but any changes in any of your items' properties won't be reflected to the UI.