8 out of 20 rated this helpful - Rate this topic

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>]
type ObservableCollection<'T> =  
    class
        inherit Collection<'T>
        interface INotifyCollectionChanged
        interface INotifyPropertyChanged
    end
See Remarks.

Type Parameters

T

The type of elements in the collection.

The ObservableCollection(T) type exposes the following members.

  NameDescription
Public methodObservableCollection(T)()Initializes a new instance of the ObservableCollection(T) class.
Public methodObservableCollection(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.
Top
  NameDescription
Public propertyCountGets the number of elements actually contained in the Collection(T). (Inherited from Collection(T).)
Public propertyItemGets or sets the element at the specified index. (Inherited from Collection(T).)
Protected propertyItemsGets a IList(T) wrapper around the Collection(T). (Inherited from Collection(T).)
Top
  NameDescription
Public methodAddAdds an object to the end of the Collection(T). (Inherited from Collection(T).)
Protected methodBlockReentrancyDisallows reentrant attempts to change this collection.
Protected methodCheckReentrancyChecks for reentrant attempts to change this collection.
Public methodClearRemoves all elements from the Collection(T). (Inherited from Collection(T).)
Protected methodClearItemsRemoves all items from the collection. (Overrides Collection(T).ClearItems().)
Public methodContainsDetermines whether an element is in the Collection(T). (Inherited from Collection(T).)
Public methodCopyToCopies the entire Collection(T) to a compatible one-dimensional Array, starting at the specified index of the target array. (Inherited from Collection(T).)
Public methodEquals(Object)Determines whether the specified Object is equal to the current Object. (Inherited from Object.)
Protected methodFinalizeAllows an object to try to free resources and perform other cleanup operations before it is reclaimed by garbage collection. (Inherited from Object.)
Public methodGetEnumeratorReturns an enumerator that iterates through the Collection(T). (Inherited from Collection(T).)
Public methodGetHashCodeServes as a hash function for a particular type. (Inherited from Object.)
Public methodGetTypeGets the Type of the current instance. (Inherited from Object.)
Public methodIndexOfSearches for the specified object and returns the zero-based index of the first occurrence within the entire Collection(T). (Inherited from Collection(T).)
Public methodInsertInserts an element into the Collection(T) at the specified index. (Inherited from Collection(T).)
Protected methodInsertItemInserts an item into the collection at the specified index. (Overrides Collection(T).InsertItem(Int32, T).)
Protected methodMemberwiseCloneCreates a shallow copy of the current Object. (Inherited from Object.)
Public methodMoveMoves the item at the specified index to a new location in the collection.
Protected methodMoveItemMoves the item at the specified index to a new location in the collection.
Protected methodOnCollectionChangedRaises the CollectionChanged event with the provided arguments.
Protected methodOnPropertyChangedRaises the PropertyChanged event with the provided arguments.
Public methodRemoveRemoves the first occurrence of a specific object from the Collection(T). (Inherited from Collection(T).)
Public methodRemoveAtRemoves the element at the specified index of the Collection(T). (Inherited from Collection(T).)
Protected methodRemoveItemRemoves the item at the specified index of the collection. (Overrides Collection(T).RemoveItem(Int32).)
Protected methodSetItemReplaces the element at the specified index. (Overrides Collection(T).SetItem(Int32, T).)
Public methodToStringReturns a string that represents the current object. (Inherited from Object.)
Top
  NameDescription
Public eventCollectionChangedOccurs when an item is added, removed, changed, moved, or the entire list is refreshed.
Protected eventPropertyChangedOccurs when a property value changes.
Top
  NameDescription
Explicit interface implemetationPrivate methodICollection.CopyToCopies the elements of the ICollection to an Array, starting at a particular Array index. (Inherited from Collection(T).)
Explicit interface implemetationPrivate propertyICollection(T).IsReadOnlyGets a value indicating whether the ICollection(T) is read-only. (Inherited from Collection(T).)
Explicit interface implemetationPrivate propertyICollection.IsSynchronizedGets a value indicating whether access to the ICollection is synchronized (thread safe). (Inherited from Collection(T).)
Explicit interface implemetationPrivate propertyICollection.SyncRootGets an object that can be used to synchronize access to the ICollection. (Inherited from Collection(T).)
Explicit interface implemetationPrivate methodIEnumerable.GetEnumeratorReturns an enumerator that iterates through a collection. (Inherited from Collection(T).)
Explicit interface implemetationPrivate methodIList.AddAdds an item to the IList. (Inherited from Collection(T).)
Explicit interface implemetationPrivate methodIList.ContainsDetermines whether the IList contains a specific value. (Inherited from Collection(T).)
Explicit interface implemetationPrivate methodIList.IndexOfDetermines the index of a specific item in the IList. (Inherited from Collection(T).)
Explicit interface implemetationPrivate methodIList.InsertInserts an item into the IList at the specified index. (Inherited from Collection(T).)
Explicit interface implemetationPrivate propertyIList.IsFixedSizeGets a value indicating whether the IList has a fixed size. (Inherited from Collection(T).)
Explicit interface implemetationPrivate propertyIList.IsReadOnlyGets a value indicating whether the IList is read-only. (Inherited from Collection(T).)
Explicit interface implemetationPrivate propertyIList.ItemGets or sets the element at the specified index. (Inherited from Collection(T).)
Explicit interface implemetationPrivate methodIList.RemoveRemoves the first occurrence of a specific object from the IList. (Inherited from Collection(T).)
Explicit interface implemetationPrivate eventINotifyPropertyChanged.PropertyChangedOccurs when a property value changes.
Top

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:

No code example is currently available or this language may not be supported.

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, 3.5, 3.0

.NET Framework Client Profile

Supported in: 4, 3.5 SP1

Windows 7, Windows Vista SP1 or later, Windows XP SP3, Windows Server 2008 (Server Core not supported), Windows Server 2008 R2 (Server Core supported with SP1 or later), Windows Server 2003 SP2

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.
Did you find this helpful?
(1500 characters remaining)
Thank you for your feedback

Community Additions

ADD
Show:
© 2014 Microsoft. All rights reserved.