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ObservableCollection<T> Class

Represents a dynamic data collection that provides notifications when items get added, removed, or when the whole list is refreshed.

Namespace:  System.Collections.ObjectModel
Assembly:  System (in System.dll)
XMLNS for XAML: Not mapped to an xmlns.
[SerializableAttribute]
public class ObservableCollection<T> : Collection<T>, 
	INotifyCollectionChanged, INotifyPropertyChanged
See Remarks.

Type Parameters

T

The type of elements in the collection.

The ObservableCollection<T> type exposes the following members.

  NameDescription
Public methodSupported by Portable Class LibrarySupported in .NET for Windows Store appsObservableCollection<T>()Initializes a new instance of the ObservableCollection<T> class.
Public methodSupported by Portable Class LibrarySupported in .NET for Windows Store appsObservableCollection<T>(IEnumerable<T>)Initializes a new instance of the ObservableCollection<T> class that contains elements copied from the specified collection.
Public methodObservableCollection<T>(List<T>)Initializes a new instance of the ObservableCollection<T> class that contains elements copied from the specified list.
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  NameDescription
Public propertySupported by Portable Class LibrarySupported in .NET for Windows Store appsCountGets the number of elements actually contained in the Collection<T>. (Inherited from Collection<T>.)
Public propertySupported by Portable Class LibrarySupported in .NET for Windows Store appsItemGets or sets the element at the specified index. (Inherited from Collection<T>.)
Protected propertySupported by Portable Class LibrarySupported in .NET for Windows Store appsItemsGets a IList<T> wrapper around the Collection<T>. (Inherited from Collection<T>.)
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  NameDescription
Public methodSupported by Portable Class LibrarySupported in .NET for Windows Store appsAddAdds an object to the end of the Collection<T>. (Inherited from Collection<T>.)
Protected methodSupported in .NET for Windows Store appsBlockReentrancyDisallows reentrant attempts to change this collection.
Protected methodSupported in .NET for Windows Store appsCheckReentrancyChecks for reentrant attempts to change this collection.
Public methodSupported by Portable Class LibrarySupported in .NET for Windows Store appsClearRemoves all elements from the Collection<T>. (Inherited from Collection<T>.)
Protected methodSupported by Portable Class LibrarySupported in .NET for Windows Store appsClearItemsRemoves all items from the collection. (Overrides Collection<T>.ClearItems().)
Public methodSupported by Portable Class LibrarySupported in .NET for Windows Store appsContainsDetermines whether an element is in the Collection<T>. (Inherited from Collection<T>.)
Public methodSupported by Portable Class LibrarySupported in .NET for Windows Store appsCopyToCopies the entire Collection<T> to a compatible one-dimensional Array, starting at the specified index of the target array. (Inherited from Collection<T>.)
Public methodSupported by Portable Class LibrarySupported in .NET for Windows Store appsEquals(Object)Determines whether the specified object is equal to the current object. (Inherited from Object.)
Protected methodSupported by Portable Class LibrarySupported in .NET for Windows Store appsFinalizeAllows an object to try to free resources and perform other cleanup operations before it is reclaimed by garbage collection. (Inherited from Object.)
Public methodSupported by Portable Class LibrarySupported in .NET for Windows Store appsGetEnumeratorReturns an enumerator that iterates through the Collection<T>. (Inherited from Collection<T>.)
Public methodSupported by Portable Class LibrarySupported in .NET for Windows Store appsGetHashCodeServes as the default hash function. (Inherited from Object.)
Public methodSupported by Portable Class LibrarySupported in .NET for Windows Store appsGetTypeGets the Type of the current instance. (Inherited from Object.)
Public methodSupported by Portable Class LibrarySupported in .NET for Windows Store appsIndexOfSearches for the specified object and returns the zero-based index of the first occurrence within the entire Collection<T>. (Inherited from Collection<T>.)
Public methodSupported by Portable Class LibrarySupported in .NET for Windows Store appsInsertInserts an element into the Collection<T> at the specified index. (Inherited from Collection<T>.)
Protected methodSupported by Portable Class LibrarySupported in .NET for Windows Store appsInsertItemInserts an item into the collection at the specified index. (Overrides Collection<T>.InsertItem(Int32, T).)
Protected methodSupported by Portable Class LibrarySupported in .NET for Windows Store appsMemberwiseCloneCreates a shallow copy of the current Object. (Inherited from Object.)
Public methodSupported in .NET for Windows Store appsMoveMoves the item at the specified index to a new location in the collection.
Protected methodSupported in .NET for Windows Store appsMoveItemMoves the item at the specified index to a new location in the collection.
Protected methodSupported by Portable Class LibrarySupported in .NET for Windows Store appsOnCollectionChangedRaises the CollectionChanged event with the provided arguments.
Protected methodSupported by Portable Class LibrarySupported in .NET for Windows Store appsOnPropertyChangedRaises the PropertyChanged event with the provided arguments.
Public methodSupported by Portable Class LibrarySupported in .NET for Windows Store appsRemoveRemoves the first occurrence of a specific object from the Collection<T>. (Inherited from Collection<T>.)
Public methodSupported by Portable Class LibrarySupported in .NET for Windows Store appsRemoveAtRemoves the element at the specified index of the Collection<T>. (Inherited from Collection<T>.)
Protected methodSupported by Portable Class LibrarySupported in .NET for Windows Store appsRemoveItemRemoves the item at the specified index of the collection. (Overrides Collection<T>.RemoveItem(Int32).)
Protected methodSupported by Portable Class LibrarySupported in .NET for Windows Store appsSetItemReplaces the element at the specified index. (Overrides Collection<T>.SetItem(Int32, T).)
Public methodSupported by Portable Class LibrarySupported in .NET for Windows Store appsToStringReturns a string that represents the current object. (Inherited from Object.)
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  NameDescription
Public eventSupported by Portable Class LibrarySupported in .NET for Windows Store appsCollectionChangedOccurs when an item is added, removed, changed, moved, or the entire list is refreshed.
Protected eventSupported by Portable Class LibrarySupported in .NET for Windows Store appsPropertyChangedOccurs when a property value changes.
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  NameDescription
Explicit interface implemetationPrivate methodSupported by Portable Class LibrarySupported in .NET for Windows Store appsICollection.CopyToCopies the elements of the ICollection to an Array, starting at a particular Array index. (Inherited from Collection<T>.)
Explicit interface implemetationPrivate propertySupported by Portable Class LibrarySupported in .NET for Windows Store appsICollection<T>.IsReadOnlyGets a value indicating whether the ICollection<T> is read-only. (Inherited from Collection<T>.)
Explicit interface implemetationPrivate propertySupported by Portable Class LibrarySupported in .NET for Windows Store appsICollection.IsSynchronizedGets a value indicating whether access to the ICollection is synchronized (thread safe). (Inherited from Collection<T>.)
Explicit interface implemetationPrivate propertySupported by Portable Class LibrarySupported in .NET for Windows Store appsICollection.SyncRootGets an object that can be used to synchronize access to the ICollection. (Inherited from Collection<T>.)
Explicit interface implemetationPrivate methodSupported by Portable Class LibrarySupported in .NET for Windows Store appsIEnumerable.GetEnumeratorReturns an enumerator that iterates through a collection. (Inherited from Collection<T>.)
Explicit interface implemetationPrivate methodSupported by Portable Class LibrarySupported in .NET for Windows Store appsIList.AddAdds an item to the IList. (Inherited from Collection<T>.)
Explicit interface implemetationPrivate methodSupported by Portable Class LibrarySupported in .NET for Windows Store appsIList.ContainsDetermines whether the IList contains a specific value. (Inherited from Collection<T>.)
Explicit interface implemetationPrivate methodSupported by Portable Class LibrarySupported in .NET for Windows Store appsIList.IndexOfDetermines the index of a specific item in the IList. (Inherited from Collection<T>.)
Explicit interface implemetationPrivate methodSupported by Portable Class LibrarySupported in .NET for Windows Store appsIList.InsertInserts an item into the IList at the specified index. (Inherited from Collection<T>.)
Explicit interface implemetationPrivate propertySupported by Portable Class LibrarySupported in .NET for Windows Store appsIList.IsFixedSizeGets a value indicating whether the IList has a fixed size. (Inherited from Collection<T>.)
Explicit interface implemetationPrivate propertySupported by Portable Class LibrarySupported in .NET for Windows Store appsIList.IsReadOnlyGets a value indicating whether the IList is read-only. (Inherited from Collection<T>.)
Explicit interface implemetationPrivate propertySupported by Portable Class LibrarySupported in .NET for Windows Store appsIList.ItemGets or sets the element at the specified index. (Inherited from Collection<T>.)
Explicit interface implemetationPrivate methodSupported by Portable Class LibrarySupported in .NET for Windows Store appsIList.RemoveRemoves the first occurrence of a specific object from the IList. (Inherited from Collection<T>.)
Explicit interface implemetationPrivate eventSupported by Portable Class LibrarySupported in .NET for Windows Store appsINotifyPropertyChanged.PropertyChangedOccurs when a property value changes.
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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<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<T> or one of the existing collection classes, such as List<T>, Collection<T>, and BindingList<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.

NoteNote

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<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<T> must be the root element, because the x:TypeArguments attribute that must be used to specify the constrained type of the generic ObservableCollection<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<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<T>.

A more straightforward way to use ObservableCollection<T> capabilities from XAML in an application is to declare your own non-generic custom collection class that derives from ObservableCollection<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 shows how to create and bind to a collection that derives from the ObservableCollection<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 : 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"));
    }
  }

  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; }
      }
  }

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.

NoteNote

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.

.NET Framework

Supported in: 4.5.1, 4.5, 4, 3.5, 3.0

.NET Framework Client Profile

Supported in: 4, 3.5 SP1

Portable Class Library

Supported in: Portable Class Library

.NET for Windows Store apps

Supported in: Windows 8

.NET for Windows Phone apps

Supported in: Windows Phone 8.1, Windows Phone 8, Silverlight 8.1

Windows Phone 8.1, Windows Phone 8, Windows 8.1, Windows Server 2012 R2, Windows 8, Windows Server 2012, Windows 7, Windows Vista SP2, Windows Server 2008 (Server Core Role not supported), Windows Server 2008 R2 (Server Core Role supported with SP1 or later; Itanium not supported)

The .NET Framework does not support all versions of every platform. For a list of the supported versions, see .NET Framework System Requirements.

Any public static (Shared in Visual Basic) members of this type are thread safe. Any instance members are not guaranteed to be thread safe.
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