Content Model: This property may be used to add items to an ItemsControl.

A common scenario is to use an ItemsControl such as a ListBox, ListView, or TreeView to display a data collection, or to bind an ItemsControl to a collection object. To bind an ItemsControl to a collection object, use the ItemsSource property. Note that the ItemsSource property supports OneWay binding by default.

When the ItemsSource property is set, the Items collection is made read-only and fixed-size.

When ItemsSource is in use, setting the property to nullNothingnullptra null reference (Nothing in Visual Basic) removes the collection and restores usage to Items, which will be an empty ItemCollection. When ItemsSource is not in use, the value of this property is nullNothingnullptra null reference (Nothing in Visual Basic), and setting it to nullNothingnullptra null reference (Nothing in Visual Basic) has no effect.

Note:
In most cases you do not need to implement your own collections. Instead, consider using ObservableCollection<(Of <(T>)>) or other existing collections. For more information, see the "Collection Objects Used as Binding Source" in Binding Sources Overview.

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 NameList
    Inherits ObservableCollection(Of PersonName)

    ' Methods
    Public Sub New()
        MyBase.Add(New PersonName("Willa", "Cather"))
        MyBase.Add(New PersonName("Isak", "Dinesen"))
        MyBase.Add(New PersonName("Victor", "Hugo"))
        MyBase.Add(New PersonName("Jules", "Verne"))
    End Sub

End Class

Public Class PersonName
    ' Methods
    Public Sub New(ByVal first As String, ByVal last As String)
        Me._firstName = first
        Me._lastName = last
    End Sub


    ' Properties
    Public Property FirstName() As String
        Get
            Return Me._firstName
        End Get
        Set(ByVal value As String)
            Me._firstName = value
        End Set
    End Property

    Public Property LastName() As String
        Get
            Return Me._lastName
        End Get
        Set(ByVal value As String)
            Me._lastName = value
        End Set
    End Property


    ' Fields
    Private _firstName As String
    Private _lastName As String
End Class

You can make the collection available for binding the same way you would with other common language runtime (CLR) objects, as described in How to: Make Data Available for Binding in XAML. For example, you can instantiate the collection in XAML and specify the collection as a resource, as shown here:

<Window
  xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
  xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
  xmlns:c="clr-namespace:SDKSample"
  x:Class="SDKSample.Window1"
  Width="400"
  Height="280"
  Title="MultiBinding Sample">
    
  <Window.Resources>
    <c:NameList x:Key="NameListData"/>


...


</Window.Resources>

You can then bind to the collection:

<ListBox Width="200"
         ItemsSource="{Binding Source={StaticResource NameListData}}"
         ItemTemplate="{StaticResource NameItemTemplate}"
         IsSynchronizedWithCurrentItem="True"/>

The definition of NameItemTemplate is not shown here. For the complete sample, see Implementing Parameterized MultiBinding Sample.

Note:
The objects in your collection must satisfy the requirements described in the Binding Sources Overview. In particular, if you are using OneWay or TwoWay (for example, you want your UI to update when the source properties change dynamically), you must implement a suitable property changed notification mechanism such as the INotifyPropertyChanged interface.

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

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