ObservableCollection<(Of <(T>)>) Class

ObservableCollection<(Of <(T>)>) Class

[SerializableAttribute]
public class ObservableCollection<T> : Collection<T>,
INotifyCollectionChanged, INotifyPropertyChanged

In many cases the data that you work with is a collection of objects. For example, a common scenario in data binding is to use an ItemsControl such as a ListBox, ListView, or TreeView to display a collection of records.

You can enumerate over any collection that implements the IEnumerable interface. However, to set up dynamic bindings so that insertions or deletions in the collection update the UI automatically, the collection must implement the INotifyCollectionChanged interface. This interface exposes the CollectionChanged event, an event that should be raised whenever the underlying collection changes.

WPF provides the ObservableCollection<(Of <(T>)>) class, which is a built-in implementation of a data collection that implements the INotifyCollectionChanged interface.

Before implementing your own collection, consider using ObservableCollection<(Of <(T>)>) or one of the existing collection classes, such as List<(Of <(T>)>), Collection<(Of <(T>)>), and BindingList<(Of <(T>)>), among many others. If you have an advanced scenario and want to implement your own collection, consider using IList, which provides a non-generic collection of objects that can be individually accessed by index. Implementing IList provides the best performance with the data binding engine.



Note:

To fully support transferring data values from binding source objects to binding targets, each object in your collection that supports bindable properties must implement an appropriate property changed notification mechanism such as the INotifyPropertyChanged interface.

For more information, see "Binding to Collections" in Data Binding Overview.

Notes on XAML Usage

ObservableCollection<(Of <(T>)>) can be used as a XAML object element in Windows Presentation Foundation (WPF), in versions 3.0 and 3.5. However, the usage has substantial limitations.

• ObservableCollection<(Of <(T>)>) must be the root element, because the x:TypeArguments attribute that must be used to specify the constrained type of the generic ObservableCollection<(Of <(T>)>) is only supported on the object element for the root element.
• You must declare an x:Class attribute (which entails that the build action for this XAML file must be Page or some other build action that compiles the XAML).
• ObservableCollection<(Of <(T>)>) is in a namespace and assembly that are not initially mapped to the default XML namespace. You must map a prefix for the namespace and assembly, and then use that prefix on the object element tag for ObservableCollection<(Of <(T>)>).

A more straightforward way to use ObservableCollection<(Of <(T>)>) capabilities from XAML in an application is to declare your own non-generic custom collection class that derives from ObservableCollection<(Of <(T>)>), and constrains it to a specific type. Then map the assembly that contains this class, and reference it as an object element in your XAML.

This example

This example shows how to create and bind to a collection that derives from the ObservableCollection<(Of <(T>)>) class, which is a collection class that provides notifications when items get added or removed.

The following example shows the implementation of a NameList collection:

public class PersonName

{

private string firstName;

private string lastName;

public PersonName(string first, string last)

{

	this.firstName = first;

	this.lastName = last;

}

public string FirstName

{

	get { return firstName; }

	set { firstName = value; }

}

public string LastName

{

	get { return lastName; }

	set { lastName = value; }

}

}

public class NameList : ObservableCollection<PersonName>

{

public NameList() : base()

{

	Add(new PersonName("Willa", "Cather"));

	Add(new PersonName("Isak", "Dinesen"));

	Add(new PersonName("Victor", "Hugo"));

	Add(new PersonName("Jules", "Verne"));

}

}