C# 4 and .NET 4

Data Binding ❘ 1053
adding list items dynamically
What if list items are added dynamically The WPF element must be notified of elements added to the list.
In the XAML code of the WPF application, a Button element is added inside a StackPanel. The Click
event is assigned to the method OnAddBook():
code snippet BooksDemo/BooksUC.xaml
In the method OnAddBook(), a new Book object is added to the list. If you test the application with the
BookFactory as it is implemented now, there’s no notification to the WPF elements that a new object has
been added to the list:
private void OnAddBook(object sender, RoutedEventArgs e)
{
((this.FindResource("books") as ObjectDataProvider).Data as
IList).Add(
new Book(".NET 3.5 Wrox Box", "Wrox Press",
"978-0470-38799-3"));
}
code snippet BooksDemo/BooksUC.xaml.cs
The object that is assigned to the DataContext must implement the interface INotifyCollectionChanged.
This interface defines the CollectionChanged event that is used by the WPF application. Instead of
implementing this interface on your own with a custom collection class, you can use the generic collection
class ObservableCollection that is defined with the namespace System.Collections.ObjectModel
in the assembly WindowsBase. Now, as a new item is added to the collection, the new item immediately
shows up in the ListBox:
public class BookFactory
{
private ObservableCollection books =
new ObservableCollection();
// ...
}
public IEnumerable GetBooks()
{
return books;
}
code snippet BooksDemo/Utilities/BookFactory.cs
data Template selector
In the previous chapter, you saw how controls can be customized with templates. You also saw how to
create a data template that defines a display for specific data types. A data template selector can create
different data templates dynamically for the same data type. A data template selector is implemented in a
class that derives from the base class DataTemplateSelector.
Here a data template selector is implemented by selecting a different template based on the publisher. Within
the user control resources these templates are defined. One template can be accessed by the key name
wroxTemplate; the other template has the key name dummiesTemplate, and the third one bookTemplate:
www.it-ebooks.info