ObservableCollection Doesn t support AddRange method so I get notified for each item added besides what about INotifyCollectionChanging

Question

I want to be able to add a range and get updated for the entire bulk   I also want to be able to cancel the action before it s done  i e  collection changing besides the  changed       Related Q Which  Net collection for adding multiple objects at once and getting notified

User · Answer

As there might be a number of operations to do on an ObservableCollection for example Clear first then AddRange and then insert "All" item for a ComboBox I ended up with folowing solution:

public static class LinqExtensions
{
    public static ICollection<T> AddRange<T>(this ICollection<T> source, IEnumerable<T> addSource)
    {
        foreach(T item in addSource)
        {
            source.Add(item);
        }

        return source;
    }
}

public class ExtendedObservableCollection<T>: ObservableCollection<T>
{
    public void Execute(Action<IList<T>> itemsAction)
    {
        itemsAction(Items);
        OnCollectionChanged(new NotifyCollectionChangedEventArgs(NotifyCollectionChangedAction.Reset));
    }
}

And example how to use it:

MyDogs.Execute(items =>
{
    items.Clear();
    items.AddRange(Context.Dogs);
    items.Insert(0, new Dog { Id = 0, Name = "All Dogs" });
});

The Reset notification will be called only once after Execute is finished processing the underlying list.

User · Answer

You will have to be careful binding the UI to your custom collection -- the Default CollectionView class only supports single notification of items

User · Answer

Proof of need for OnPropertyChanged  Count   and OnPropertyChanged  Item     calls in order to behave as per ObservableCollection  Note that I don t know what the consequences are if you don t bother   Here is a test method that shows that there are two PropertyChange events for each add in a normal observable collection  One for  Count  and one for  Item       TestMethod  public void TestAddSinglesInOldObsevableCollection       int colChangedEvents   0    int propChangedEvents   0    var collection   new ObservableCollection lt object gt       collection CollectionChanged     sender  e    gt    colChangedEvents          collection as INotifyPropertyChanged  PropertyChanged     sender  e    gt    propChangedEvents         collection Add new object       collection Add new object       collection Add new object       Assert AreEqual 3  colChangedEvents     Assert AreEqual 6  propChangedEvents        Shimmy   swap the standard for your collection and change to an add range and you will get zero PropertyChanges  Note that collection change does work fine  but not doing exactly what ObservableCollection does  So Test for shimmy collection looks like this    TestMethod  public void TestShimmyAddRange       int colChangedEvents   0    int propChangedEvents   0    var collection   new ShimmyObservableCollection lt object gt       collection CollectionChanged     sender  e    gt    colChangedEvents          collection as INotifyPropertyChanged  PropertyChanged     sender  e    gt    propChangedEvents         collection AddRange new        new object    new object    new object    new object        4 objects at once   Assert AreEqual 1  colChangedEvents      great  just one    Assert AreEqual 2  propChangedEvents     fails  no events        FYI here is code from InsertItem  also called by Add  from ObservableCollection   protected override void InsertItem int index  T item      base CheckReentrancy      base InsertItem index  item     base OnPropertyChanged  Count      base OnPropertyChanged  Item        base OnCollectionChanged NotifyCollectionChangedAction Add  item  index

User · Answer

Yes  adding your own Custom Observable Collection would be fair enough  Don t forget to raise appropriate events regardless whether it is used by UI for the moment or not    You will have to raise property change notification for  Item    property  required by WPF side and bound controls  as well as NotifyCollectionChangedEventArgs with a set of items added  your range    I ve did such things  as well as sorting support and some other stuff  and had no problems with both Presentation and Code Behind layers

User · Answer

Please refer to the updated and optimized C  7 version  I didn t want to remove the VB NET version so I just posted it in a separate answer   Go to updated version  Seems it s not supported  I implemented by myself  FYI  hope it to be helpful   I updated the VB version and from now on it raises an event before changing the collection so you can regret  useful when using with DataGrid  ListView and many more  that you can show an  Are you sure  confirmation to the user   the updated VB version is in the bottom of this message   Please accept my apology that the screen is too narrow to contain my code  I don t like it either   VB NET   Imports System Collections Specialized  Namespace System Collections ObjectModel          lt summary gt          Represents a dynamic data collection that provides notifications when items get added  removed  or when the whole list is refreshed           lt  summary gt           lt typeparam name  T  gt  lt  typeparam gt      Public Class ObservableRangeCollection Of T    Inherits System Collections ObjectModel ObservableCollection Of T                lt summary gt              Adds the elements of the specified collection to the end of the ObservableCollection Of T                lt  summary gt          Public Sub AddRange ByVal collection As IEnumerable Of T               For Each i In collection                 Items Add i              Next             OnCollectionChanged New NotifyCollectionChangedEventArgs NotifyCollectionChangedAction Reset           End Sub               lt summary gt              Removes the first occurence of each item in the specified collection from ObservableCollection Of T                lt  summary gt          Public Sub RemoveRange ByVal collection As IEnumerable Of T               For Each i In collection                 Items Remove i              Next              OnCollectionChanged New NotifyCollectionChangedEventArgs NotifyCollectionChangedAction Reset           End Sub               lt summary gt              Clears the current collection and replaces it with the specified item               lt  summary gt          Public Sub Replace ByVal item As T              ReplaceRange New T    item           End Sub              lt summary gt              Clears the current collection and replaces it with the specified collection               lt  summary gt          Public Sub ReplaceRange ByVal collection As IEnumerable Of T               Dim old   Items ToList             Items Clear               For Each i In collection                 Items Add i              Next             OnCollectionChanged New NotifyCollectionChangedEventArgs NotifyCollectionChangedAction Reset           End Sub               lt summary gt              Initializes a new instance of the System Collections ObjectModel ObservableCollection Of T  class               lt  summary gt               lt remarks gt  lt  remarks gt          Public Sub New               MyBase New           End Sub              lt summary gt              Initializes a new instance of the System Collections ObjectModel ObservableCollection Of T  class that contains elements copied from the specified collection               lt  summary gt               lt param name  collection  gt collection  The collection from which the elements are copied  lt  param gt               lt exception cref  System ArgumentNullException  gt The collection parameter cannot be null  lt  exception gt          Public Sub New ByVal collection As IEnumerable Of T               MyBase New collection          End Sub     End Class     End Namespace   C    using System  using System Collections Generic  using System Collections ObjectModel  using System Collections Specialized  using System Linq        lt summary gt       Represents a dynamic data collection that provides notifications when items get added  removed  or when the whole list is refreshed        lt  summary gt        lt typeparam name  T  gt  lt  typeparam gt   public class ObservableRangeCollection lt T gt    ObservableCollection lt T gt             lt summary gt           Adds the elements of the specified collection to the end of the ObservableCollection Of T             lt  summary gt       public void AddRange IEnumerable lt T gt  collection                if  collection    null  throw new ArgumentNullException  collection             foreach  var i in collection  Items Add i           OnCollectionChanged new NotifyCollectionChangedEventArgs NotifyCollectionChangedAction Reset                    lt summary gt           Removes the first occurence of each item in the specified collection from ObservableCollection Of T             lt  summary gt       public void RemoveRange IEnumerable lt T gt  collection                if  collection    null  throw new ArgumentNullException  collection             foreach  var i in collection  Items Remove i           OnCollectionChanged new NotifyCollectionChangedEventArgs NotifyCollectionChangedAction Reset                    lt summary gt           Clears the current collection and replaces it with the specified item            lt  summary gt       public void Replace T item                ReplaceRange new T     item                     lt summary gt           Clears the current collection and replaces it with the specified collection            lt  summary gt       public void ReplaceRange IEnumerable lt T gt  collection                if  collection    null  throw new ArgumentNullException  collection             Items Clear            foreach  var i in collection  Items Add i           OnCollectionChanged new NotifyCollectionChangedEventArgs NotifyCollectionChangedAction Reset                    lt summary gt           Initializes a new instance of the System Collections ObjectModel ObservableCollection Of T  class            lt  summary gt       public ObservableRangeCollection             base                 lt summary gt           Initializes a new instance of the System Collections ObjectModel ObservableCollection Of T  class that contains elements copied from the specified collection            lt  summary gt            lt param name  collection  gt collection  The collection from which the elements are copied  lt  param gt            lt exception cref  System ArgumentNullException  gt The collection parameter cannot be null  lt  exception gt       public ObservableRangeCollection IEnumerable lt T gt  collection            base collection          Update - Observable range collection with collection changing notification  Imports System Collections Specialized Imports System ComponentModel Imports System Collections ObjectModel  Public Class ObservableRangeCollection Of T    Inherits ObservableCollection Of T    Implements INotifyCollectionChanging Of T           lt summary gt          Initializes a new instance of the System Collections ObjectModel ObservableCollection Of T  class           lt  summary gt           lt remarks gt  lt  remarks gt      Public Sub New           MyBase New       End Sub           lt summary gt          Initializes a new instance of the System Collections ObjectModel ObservableCollection Of T  class that contains elements copied from the specified collection           lt  summary gt           lt param name  collection  gt collection  The collection from which the elements are copied  lt  param gt           lt exception cref  System ArgumentNullException  gt The collection parameter cannot be null  lt  exception gt      Public Sub New ByVal collection As IEnumerable Of T           MyBase New collection      End Sub           lt summary gt          Adds the elements of the specified collection to the end of the ObservableCollection Of T            lt  summary gt      Public Sub AddRange ByVal collection As IEnumerable Of T           Dim ce As New NotifyCollectionChangingEventArgs Of T  NotifyCollectionChangedAction Add  collection          OnCollectionChanging ce          If ce Cancel Then Exit Sub          Dim index   Items Count - 1         For Each i In collection             Items Add i          Next          OnCollectionChanged New NotifyCollectionChangedEventArgs NotifyCollectionChangedAction Add  collection  index       End Sub            lt summary gt          Inserts the collection at specified index           lt  summary gt      Public Sub InsertRange ByVal index As Integer  ByVal Collection As IEnumerable Of T           Dim ce As New NotifyCollectionChangingEventArgs Of T  NotifyCollectionChangedAction Add  Collection          OnCollectionChanging ce          If ce Cancel Then Exit Sub          For Each i In Collection             Items Insert index  i          Next          OnCollectionChanged New NotifyCollectionChangedEventArgs NotifyCollectionChangedAction Reset       End Sub            lt summary gt          Removes the first occurence of each item in the specified collection from ObservableCollection Of T            lt  summary gt      Public Sub RemoveRange ByVal collection As IEnumerable Of T           Dim ce As New NotifyCollectionChangingEventArgs Of T  NotifyCollectionChangedAction Remove  collection          OnCollectionChanging ce          If ce Cancel Then Exit Sub          For Each i In collection             Items Remove i          Next          OnCollectionChanged New NotifyCollectionChangedEventArgs NotifyCollectionChangedAction Reset       End Sub             lt summary gt          Clears the current collection and replaces it with the specified item           lt  summary gt      Public Sub Replace ByVal item As T          ReplaceRange New T    item       End Sub           lt summary gt          Clears the current collection and replaces it with the specified collection           lt  summary gt      Public Sub ReplaceRange ByVal collection As IEnumerable Of T           Dim ce As New NotifyCollectionChangingEventArgs Of T  NotifyCollectionChangedAction Replace  Items          OnCollectionChanging ce          If ce Cancel Then Exit Sub          Items Clear           For Each i In collection             Items Add i          Next         OnCollectionChanged New NotifyCollectionChangedEventArgs NotifyCollectionChangedAction Reset       End Sub      Protected Overrides Sub ClearItems           Dim e As New NotifyCollectionChangingEventArgs Of T  NotifyCollectionChangedAction Reset  Items          OnCollectionChanging e           If e Cancel Then Exit Sub          MyBase ClearItems       End Sub      Protected Overrides Sub InsertItem ByVal index As Integer  ByVal item As T          Dim ce As New NotifyCollectionChangingEventArgs Of T  NotifyCollectionChangedAction Add  item          OnCollectionChanging ce          If ce Cancel Then Exit Sub          MyBase InsertItem index  item      End Sub      Protected Overrides Sub MoveItem ByVal oldIndex As Integer  ByVal newIndex As Integer          Dim ce As New NotifyCollectionChangingEventArgs Of T            OnCollectionChanging ce          If ce Cancel Then Exit Sub          MyBase MoveItem oldIndex  newIndex      End Sub      Protected Overrides Sub RemoveItem ByVal index As Integer          Dim ce As New NotifyCollectionChangingEventArgs Of T  NotifyCollectionChangedAction Remove  Items index           OnCollectionChanging ce          If ce Cancel Then Exit Sub          MyBase RemoveItem index      End Sub      Protected Overrides Sub SetItem ByVal index As Integer  ByVal item As T          Dim ce As New NotifyCollectionChangingEventArgs Of T  NotifyCollectionChangedAction Replace  Items index           OnCollectionChanging ce          If ce Cancel Then Exit Sub          MyBase SetItem index  item      End Sub      Protected Overrides Sub OnCollectionChanged ByVal e As Specialized NotifyCollectionChangedEventArgs          If e NewItems IsNot Nothing Then             For Each i As T In e NewItems                 If TypeOf i Is INotifyPropertyChanged Then AddHandler DirectCast i  INotifyPropertyChanged  PropertyChanged  AddressOf Item PropertyChanged             Next         End If         MyBase OnCollectionChanged e      End Sub      Private Sub Item PropertyChanged ByVal sender As T  ByVal e As ComponentModel PropertyChangedEventArgs          OnCollectionChanged New NotifyCollectionChangedEventArgs NotifyCollectionChangedAction Reset  sender  IndexOf sender        End Sub      Public Event CollectionChanging ByVal sender As Object  ByVal e As NotifyCollectionChangingEventArgs Of T   Implements INotifyCollectionChanging Of T  CollectionChanging     Protected Overridable Sub OnCollectionChanging ByVal e As NotifyCollectionChangingEventArgs Of T           RaiseEvent CollectionChanging Me  e      End Sub End Class   Public Interface INotifyCollectionChanging Of T      Event CollectionChanging ByVal sender As Object  ByVal e As NotifyCollectionChangingEventArgs Of T   End Interface  Public Class NotifyCollectionChangingEventArgs Of T    Inherits CancelEventArgs      Public Sub New           m Action   NotifyCollectionChangedAction Move         m Items   New T          End Sub      Public Sub New ByVal action As NotifyCollectionChangedAction  ByVal item As T          m Action   action         m Items   New T    item      End Sub      Public Sub New ByVal action As NotifyCollectionChangedAction  ByVal items As IEnumerable Of T           m Action   action         m Items   items     End Sub      Private m Action As NotifyCollectionChangedAction     Public ReadOnly Property Action   As NotifyCollectionChangedAction         Get             Return m Action         End Get     End Property      Private m Items As IList     Public ReadOnly Property Items   As IEnumerable Of T          Get             Return m Items         End Get     End Property End Class

User · Answer

The C  summarized descendant   More reading  http   blogs msdn com b nathannesbit archive 2009 04 20 addrange-and-observablecollection aspx  public sealed class ObservableCollectionEx lt T gt    ObservableCollection lt T gt         region Ctor      public ObservableCollectionEx                    public ObservableCollectionEx List lt T gt  list    base list                   public ObservableCollectionEx IEnumerable lt T gt  collection    base collection                    endregion           lt summary gt           Adds the elements of the specified collection to the end of the ObservableCollection Of T             lt  summary gt       public void AddRange          IEnumerable lt T gt  itemsToAdd          ECollectionChangeNotificationMode notificationMode   ECollectionChangeNotificationMode Add                if  itemsToAdd    null                        throw new ArgumentNullException  itemsToAdd                      CheckReentrancy             if  notificationMode    ECollectionChangeNotificationMode Reset                        foreach  var i in itemsToAdd                                Items Add i                              OnPropertyChanged new PropertyChangedEventArgs  Count                 OnPropertyChanged new PropertyChangedEventArgs  Item                   OnCollectionChanged new NotifyCollectionChangedEventArgs NotifyCollectionChangedAction Reset                 return                     int startIndex   Count          var changedItems   itemsToAdd is List lt T gt     List lt T gt   itemsToAdd   new List lt T gt  itemsToAdd           foreach  var i in changedItems                        Items Add i                      OnPropertyChanged new PropertyChangedEventArgs  Count             OnPropertyChanged new PropertyChangedEventArgs  Item               OnCollectionChanged new NotifyCollectionChangedEventArgs NotifyCollectionChangedAction Add  changedItems  startIndex               public enum ECollectionChangeNotificationMode                    lt summary gt              Notifies that only a portion of data was changed and supplies the changed items  not supported by some elements              like CollectionView class                lt  summary gt          Add                lt summary gt              Notifies that the entire collection was changed  does not supply the changed items  may be inneficient with large             collections as requires the full update even if a small portion of items was added                lt  summary gt          Reset

User · Answer

ObservableRangeCollection should pass a test like   Test  public void TestAddRangeWhileBoundToListCollectionView         int collectionChangedEventsCounter   0      int propertyChangedEventsCounter   0      var collection   new ObservableRangeCollection lt object gt          collection CollectionChanged     sender  e    gt    collectionChangedEventsCounter            collection as INotifyPropertyChanged  PropertyChanged     sender  e    gt    propertyChangedEventsCounter            var list   new ListCollectionView collection        collection AddRange new     new object    new object    new object    new object            Assert AreEqual 4  collection Count       Assert AreEqual 1  collectionChangedEventsCounter       Assert AreEqual 2  propertyChangedEventsCounter       otherwise we get   System NotSupportedException   Range actions are not supported    while using with a control   I do not see an ideal solution  but NotifyCollectionChangedAction Reset instead of Add Remove partially solve the problem  See http   blogs msdn com b nathannesbit archive 2009 04 20 addrange-and-observablecollection aspx as was mentioned by net prog

User · Answer

Here s a modification of the accepted answer to provide more functionality   RangeCollection cs   public class RangeCollection lt T gt    ObservableCollection lt T gt         region Members           lt summary gt          Occurs when a single item is added           lt  summary gt      public event EventHandler lt ItemAddedEventArgs lt T gt  gt  ItemAdded            lt summary gt          Occurs when a single item is inserted           lt  summary gt      public event EventHandler lt ItemInsertedEventArgs lt T gt  gt  ItemInserted            lt summary gt          Occurs when a single item is removed           lt  summary gt      public event EventHandler lt ItemRemovedEventArgs lt T gt  gt  ItemRemoved            lt summary gt          Occurs when a single item is replaced           lt  summary gt      public event EventHandler lt ItemReplacedEventArgs lt T gt  gt  ItemReplaced            lt summary gt          Occurs when items are added to this           lt  summary gt      public event EventHandler lt ItemsAddedEventArgs lt T gt  gt  ItemsAdded            lt summary gt          Occurs when items are removed from this           lt  summary gt      public event EventHandler lt ItemsRemovedEventArgs lt T gt  gt  ItemsRemoved            lt summary gt          Occurs when items are replaced within this           lt  summary gt      public event EventHandler lt ItemsReplacedEventArgs lt T gt  gt  ItemsReplaced            lt summary gt          Occurs when entire collection is cleared           lt  summary gt      public event EventHandler lt ItemsClearedEventArgs lt T gt  gt  ItemsCleared            lt summary gt          Occurs when entire collection is replaced           lt  summary gt      public event EventHandler lt CollectionReplacedEventArgs lt T gt  gt  CollectionReplaced        endregion       region Helper Methods           lt summary gt          Throws exception if any of the specified objects are null           lt  summary gt      private void Check params T   Items                foreach  T Item in Items                        if  Item    null                                throw new ArgumentNullException  Item cannot be null                                        private void Check IEnumerable lt T gt  Items                if  Items    null  throw new ArgumentNullException  Items cannot be null                private void Check IEnumerable lt IEnumerable lt T gt  gt  Items                if  Items    null  throw new ArgumentNullException  Items cannot be null                private void RaiseChanged NotifyCollectionChangedAction Action                this OnPropertyChanged new PropertyChangedEventArgs  Count             this OnPropertyChanged new PropertyChangedEventArgs  Item               this OnCollectionChanged new NotifyCollectionChangedEventArgs NotifyCollectionChangedAction Reset                endregion       region Bulk Methods           lt summary gt           Adds the elements of the specified collection to the end of this           lt  summary gt       public void AddRange IEnumerable lt T gt  NewItems                this Check NewItems           foreach  var i in NewItems  this Items Add i           this RaiseChanged NotifyCollectionChangedAction Reset           this OnItemsAdded new ItemsAddedEventArgs lt T gt  NewItems                    lt summary gt          Adds variable IEnumerable lt T gt  to this           lt  summary gt           lt param name  List  gt  lt  param gt      public void AddRange params IEnumerable lt T gt    NewItems                this Check NewItems           foreach  IEnumerable lt T gt  Items in NewItems  foreach  T Item in Items  this Items Add Item           this RaiseChanged NotifyCollectionChangedAction Reset             TO-DO  Raise OnItemsAdded with combined IEnumerable lt T gt                   lt summary gt           Removes the first occurence of each item in the specified collection            lt  summary gt       public void Remove IEnumerable lt T gt  OldItems                this Check OldItems           foreach  var i in OldItems  Items Remove i           this RaiseChanged NotifyCollectionChangedAction Reset           OnItemsRemoved new ItemsRemovedEventArgs lt T gt  OldItems                    lt summary gt          Removes all occurences of each item in the specified collection           lt  summary gt           lt param name  itemsToRemove  gt  lt  param gt      public void RemoveAll IEnumerable lt T gt  OldItems                this Check OldItems           var set   new HashSet lt T gt  OldItems           var list   this as List lt T gt           int i   0          while  i  lt  this Count  if  set Contains this i    this RemoveAt i   else i            this RaiseChanged NotifyCollectionChangedAction Reset           OnItemsRemoved new ItemsRemovedEventArgs lt T gt  OldItems                    lt summary gt           Replaces all occurences of a single item with specified item           lt  summary gt       public void ReplaceAll T Old  T New                this Check Old  New           this Replace Old  New  false           this RaiseChanged NotifyCollectionChangedAction Reset           this OnItemReplaced new ItemReplacedEventArgs lt T gt  Old  New                    lt summary gt           Clears this and adds specified collection            lt  summary gt       public void ReplaceCollection IEnumerable lt T gt  NewItems  bool SupressEvent   false                this Check NewItems           IEnumerable lt T gt  OldItems   new List lt T gt  this Items           this Items Clear            foreach  T Item in NewItems  this Items Add Item           this RaiseChanged NotifyCollectionChangedAction Reset           this OnReplaced new CollectionReplacedEventArgs lt T gt  OldItems  NewItems               private void Replace T Old  T New  bool BreakFirst                List lt T gt  Cloned   new List lt T gt  this Items           int i   0          foreach  T Item in Cloned                        if  Item Equals Old                                 this Items Remove Item                   this Items Insert i  New                   if  BreakFirst  break                            i                              lt summary gt           Replaces the first occurence of a single item with specified item           lt  summary gt       public void Replace T Old  T New                this Check Old  New           this Replace Old  New  true           this RaiseChanged NotifyCollectionChangedAction Reset           this OnItemReplaced new ItemReplacedEventArgs lt T gt  Old  New                endregion       region  New Methods           lt summary gt          Removes a single item           lt  summary gt           lt param name  Item  gt  lt  param gt      public new void Remove T Item                this Check Item           base Remove Item           OnItemRemoved new ItemRemovedEventArgs lt T gt  Item                    lt summary gt          Removes a single item at specified index           lt  summary gt           lt param name  i  gt  lt  param gt      public new void RemoveAt int i                T OldItem   this Items i     This will throw first if null         base RemoveAt i           OnItemRemoved new ItemRemovedEventArgs lt T gt  OldItem                    lt summary gt          Clears this           lt  summary gt      public new void Clear                 IEnumerable lt T gt  OldItems   new List lt T gt  this Items           this Items Clear            this RaiseChanged NotifyCollectionChangedAction Reset           this OnCleared new ItemsClearedEventArgs lt T gt  OldItems                    lt summary gt          Adds a single item to end of this           lt  summary gt           lt param name  t  gt  lt  param gt      public new void Add T Item                this Check Item           base Add Item           this OnItemAdded new ItemAddedEventArgs lt T gt  Item                    lt summary gt          Inserts a single item at specified index           lt  summary gt           lt param name  i  gt  lt  param gt           lt param name  t  gt  lt  param gt      public new void Insert int i  T Item                this Check Item           base Insert i  Item           this OnItemInserted new ItemInsertedEventArgs lt T gt  Item  i                    lt summary gt          Returns list of T ToString             lt  summary gt           lt returns gt  lt  returns gt      public new IEnumerable lt string gt  ToString                 foreach  T Item in this  yield return Item ToString                endregion       region Event Methods      private void OnItemAdded ItemAddedEventArgs lt T gt  i                if  this ItemAdded    null  this ItemAdded this  new ItemAddedEventArgs lt T gt  i NewItem               private void OnItemInserted ItemInsertedEventArgs lt T gt  i                if  this ItemInserted    null  this ItemInserted this  new ItemInsertedEventArgs lt T gt  i NewItem  i Index               private void OnItemRemoved ItemRemovedEventArgs lt T gt  i                if  this ItemRemoved    null  this ItemRemoved this  new ItemRemovedEventArgs lt T gt  i OldItem               private void OnItemReplaced ItemReplacedEventArgs lt T gt  i                if  this ItemReplaced    null  this ItemReplaced this  new ItemReplacedEventArgs lt T gt  i OldItem  i NewItem               private void OnItemsAdded ItemsAddedEventArgs lt T gt  i                if  this ItemsAdded    null  this ItemsAdded this  new ItemsAddedEventArgs lt T gt  i NewItems               private void OnItemsRemoved ItemsRemovedEventArgs lt T gt  i                if  this ItemsRemoved    null  this ItemsRemoved this  new ItemsRemovedEventArgs lt T gt  i OldItems               private void OnItemsReplaced ItemsReplacedEventArgs lt T gt  i                if  this ItemsReplaced    null  this ItemsReplaced this  new ItemsReplacedEventArgs lt T gt  i OldItems  i NewItems               private void OnCleared ItemsClearedEventArgs lt T gt  i                if  this ItemsCleared    null  this ItemsCleared this  new ItemsClearedEventArgs lt T gt  i OldItems               private void OnReplaced CollectionReplacedEventArgs lt T gt  i                if  this CollectionReplaced    null  this CollectionReplaced this  new CollectionReplacedEventArgs lt T gt  i OldItems  i NewItems                endregion       region RangeCollection           lt summary gt           Initializes a new instance            lt  summary gt       public RangeCollection     base                 lt summary gt           Initializes a new instance from specified enumerable            lt  summary gt       public RangeCollection IEnumerable lt T gt  Collection    base Collection                lt summary gt           Initializes a new instance from specified list           lt  summary gt       public RangeCollection List lt T gt  List    base List                lt summary gt          Initializes a new instance with variable T           lt  summary gt      public RangeCollection params T   Items    base                 this AddRange Items                   lt summary gt          Initializes a new instance with variable enumerable           lt  summary gt      public RangeCollection params IEnumerable lt T gt    Items    base                 this AddRange Items               endregion     Events Classes   public class CollectionReplacedEventArgs lt T gt    ReplacedEventArgs lt T gt        public CollectionReplacedEventArgs IEnumerable lt T gt  Old  IEnumerable lt T gt  New    base Old  New         public class ItemAddedEventArgs lt T gt    EventArgs       public T NewItem      public ItemAddedEventArgs T t                this NewItem   t           public class ItemInsertedEventArgs lt T gt    EventArgs       public int Index      public T NewItem      public ItemInsertedEventArgs T t  int i                this NewItem   t          this Index   i           public class ItemRemovedEventArgs lt T gt    EventArgs       public T OldItem      public ItemRemovedEventArgs T t                this OldItem   t           public class ItemReplacedEventArgs lt T gt    EventArgs       public T OldItem      public T NewItem      public ItemReplacedEventArgs T Old  T New                this OldItem   Old          this NewItem   New           public class ItemsAddedEventArgs lt T gt    EventArgs       public IEnumerable lt T gt  NewItems      public ItemsAddedEventArgs IEnumerable lt T gt  t                this NewItems   t           public class ItemsClearedEventArgs lt T gt    RemovedEventArgs lt T gt        public ItemsClearedEventArgs IEnumerable lt T gt  Old    base Old         public class ItemsRemovedEventArgs lt T gt    RemovedEventArgs lt T gt        public ItemsRemovedEventArgs IEnumerable lt T gt  Old    base Old         public class ItemsReplacedEventArgs lt T gt    ReplacedEventArgs lt T gt        public ItemsReplacedEventArgs IEnumerable lt T gt  Old  IEnumerable lt T gt  New    base Old  New         public class RemovedEventArgs lt T gt    EventArgs       public IEnumerable lt T gt  OldItems      public RemovedEventArgs IEnumerable lt T gt  Old                this OldItems   Old           public class ReplacedEventArgs lt T gt    EventArgs       public IEnumerable lt T gt  OldItems      public IEnumerable lt T gt  NewItems      public ReplacedEventArgs IEnumerable lt T gt  Old  IEnumerable lt T gt  New                this OldItems   Old          this NewItems   New            Note  I did not manually raise OnCollectionChanged in the base methods because it appears only to be possible to create a CollectionChangedEventArgs using the Reset action  If you try to raise OnCollectionChanged using Reset for a single item change  your items control will appear to flicker  which is something you want to avoid

User · Answer

I think AddRange is better implemented like so    public void AddRange IEnumerable lt T gt  collection        foreach  var i in collection  Items Add i       OnCollectionChanged          new NotifyCollectionChangedEventArgs NotifyCollectionChangedAction Reset        It saves you a list copy  Also if you want to micro-optimise you could do adds for up to N items and if more than N items where added do a reset

User · Answer

Here is some additional help for collection changed and UI issues

User · Answer

You can also use this code to extend ObservableCollection   public static class ObservableCollectionExtend       public static void AddRange lt TSource gt  this ObservableCollection lt TSource gt  source  IEnumerable lt TSource gt  items                foreach  var item in items                        source Add item                       Then you don t need to change class in existing code

User · Answer

First of all  please vote and comment on the API request on the  NET repo   Here s my optimized version of the ObservableRangeCollection  optimized version of James Montemagno s one    It performs very fast and is meant to reuse existing elements when possible and avoid unnecessary events  or batching them into one  when possible  The ReplaceRange method replaces removes adds the required elements by the appropriate indices and batches the possible events   Tested on Xamarin Forms UI with great results for very frequent updates to the large collection  5-7 updates per second    Note  Since WPF is not accustomed to work with range operations  it will throw a NotSupportedException  when using the ObservableRangeCollection from below in WPF UI-related work  such as binding it to a ListBox etc   you can still use the ObservableRangeCollection lt T gt  if not bound to UI   However you can use the WpfObservableRangeCollection lt T gt  workaround  The real solution would be creating a CollectionView that knows how to deal with range operations  but I still didn t have the time to implement this   RAW Code - open as Raw  then do Ctrl A to select all  then Ctrl C to copy      Licensed to the  NET Foundation under one or more agreements     The  NET Foundation licenses this file to you under the MIT license     See the LICENSE file in the project root for more information   using System Collections Generic  using System Collections Specialized  using System ComponentModel  using System Diagnostics   namespace System Collections ObjectModel          lt summary gt        Implementation of a dynamic data collection based on generic Collection amp lt T amp gt         implementing INotifyCollectionChanged to notify listeners       when items get added  removed or the whole list is refreshed         lt  summary gt    public class ObservableRangeCollection lt T gt    ObservableCollection lt T gt            ------------------------------------------------------                Private Fields              ------------------------------------------------------       region Private Fields          NonSerialized      private DeferredEventsCollection  deferredEvents       endregion Private Fields         ------------------------------------------------------                Constructors              ------------------------------------------------------       region Constructors          lt summary gt          Initializes a new instance of ObservableCollection that is empty and has default initial capacity           lt  summary gt      public ObservableRangeCollection                 lt summary gt          Initializes a new instance of the ObservableCollection class that contains         elements copied from the specified collection and has sufficient capacity         to accommodate the number of elements copied           lt  summary gt           lt param name  collection  gt The collection whose elements are copied to the new list  lt  param gt           lt remarks gt          The elements are copied onto the ObservableCollection in the         same order they are read by the enumerator of the collection           lt  remarks gt           lt exception cref  ArgumentNullException  gt  collection is a null reference  lt  exception gt      public ObservableRangeCollection IEnumerable lt T gt  collection    base collection                lt summary gt          Initializes a new instance of the ObservableCollection class         that contains elements copied from the specified list          lt  summary gt           lt param name  list  gt The list whose elements are copied to the new list  lt  param gt           lt remarks gt          The elements are copied onto the ObservableCollection in the         same order they are read by the enumerator of the list           lt  remarks gt           lt exception cref  ArgumentNullException  gt  list is a null reference  lt  exception gt      public ObservableRangeCollection List lt T gt  list    base list            endregion Constructors        ------------------------------------------------------                Public Methods              ------------------------------------------------------       region Public Methods           lt summary gt          Adds the elements of the specified collection to the end of the  lt see cref  ObservableCollection T    gt            lt  summary gt           lt param name  collection  gt          The collection whose elements should be added to the end of the  lt see cref  ObservableCollection T    gt           The collection itself cannot be null  but it can contain elements that are null  if type T is a reference type           lt  param gt           lt exception cref  ArgumentNullException  gt  lt paramref name  collection   gt  is null  lt  exception gt      public void AddRange IEnumerable lt T gt  collection              InsertRange Count  collection                   lt summary gt          Inserts the elements of a collection into the  lt see cref  ObservableCollection T    gt  at the specified index           lt  summary gt           lt param name  index  gt The zero-based index at which the new elements should be inserted  lt  param gt           lt param name  collection  gt The collection whose elements should be inserted into the List lt T gt           The collection itself cannot be null  but it can contain elements that are null  if type T is a reference type  lt  param gt                           lt exception cref  ArgumentNullException  gt  lt paramref name  collection   gt  is null  lt  exception gt           lt exception cref  ArgumentOutOfRangeException  gt  lt paramref name  index   gt  is not in the collection range  lt  exception gt      public void InsertRange int index  IEnumerable lt T gt  collection              if  collection    null          throw new ArgumentNullException nameof collection          if  index  lt  0          throw new ArgumentOutOfRangeException nameof index          if  index  gt  Count          throw new ArgumentOutOfRangeException nameof index           if  collection is ICollection lt T gt  countable                  if  countable Count    0                      return                          else if   ContainsAny collection                   return                 CheckReentrancy             expand the following couple of lines when adding more constructors        var target    List lt T gt  Items        target InsertRange index  collection          OnEssentialPropertiesChanged           if    collection is IList list           list   new List lt T gt  collection          OnCollectionChanged new NotifyCollectionChangedEventArgs NotifyCollectionChangedAction Add  list  index                     lt summary gt           Removes the first occurence of each item in the specified collection from the  lt see cref  ObservableCollection T    gt            lt  summary gt           lt param name  collection  gt The items to remove  lt  param gt                   lt exception cref  ArgumentNullException  gt  lt paramref name  collection   gt  is null  lt  exception gt      public void RemoveRange IEnumerable lt T gt  collection              if  collection    null          throw new ArgumentNullException nameof collection           if  Count    0                  return                else if  collection is ICollection lt T gt  countable                  if  countable Count    0            return          else if  countable Count    1            using  IEnumerator lt T gt  enumerator   countable GetEnumerator                            enumerator MoveNext                Remove enumerator Current               return                            else if    ContainsAny collection                    return                 CheckReentrancy           var clusters   new Dictionary lt int  List lt T gt  gt           var lastIndex   -1        List lt T gt  lastCluster   null        foreach  T item in collection                  var index   IndexOf item           if  index  lt  0                      continue                     Items RemoveAt index            if  lastIndex    index  amp  amp  lastCluster    null                      lastCluster Add item                     else                     clusters lastIndex   index    lastCluster   new List lt T gt    item                             OnEssentialPropertiesChanged           if  Count    0          OnCollectionReset          else         foreach  KeyValuePair lt int  List lt T gt  gt  cluster in clusters            OnCollectionChanged new NotifyCollectionChangedEventArgs NotifyCollectionChangedAction Remove  cluster Value  cluster Key                     lt summary gt          Iterates over the collection and removes all items that satisfy the specified match           lt  summary gt           lt remarks gt The complexity is O n   lt  remarks gt           lt param name  match  gt  lt  param gt           lt returns gt Returns the number of elements that where  lt  returns gt           lt exception cref  ArgumentNullException  gt  lt paramref name  match   gt  is null  lt  exception gt      public int RemoveAll Predicate lt T gt  match              return RemoveAll 0  Count  match                   lt summary gt          Iterates over the specified range within the collection and removes all items that satisfy the specified match           lt  summary gt           lt remarks gt The complexity is O n   lt  remarks gt           lt param name  index  gt The index of where to start performing the search  lt  param gt           lt param name  count  gt The number of items to iterate on  lt  param gt           lt param name  match  gt  lt  param gt           lt returns gt Returns the number of elements that where  lt  returns gt           lt exception cref  ArgumentOutOfRangeException  gt  lt paramref name  index   gt  is out of range  lt  exception gt           lt exception cref  ArgumentOutOfRangeException  gt  lt paramref name  count   gt  is out of range  lt  exception gt           lt exception cref  ArgumentNullException  gt  lt paramref name  match   gt  is null  lt  exception gt      public int RemoveAll int index  int count  Predicate lt T gt  match              if  index  lt  0          throw new ArgumentOutOfRangeException nameof index          if  count  lt  0          throw new ArgumentOutOfRangeException nameof count          if  index   count  gt  Count          throw new ArgumentOutOfRangeException nameof index          if  match    null          throw new ArgumentNullException nameof match           if  Count    0          return 0         List lt T gt  cluster   null        var clusterIndex   -1        var removedCount   0         using  BlockReentrancy          using  DeferEvents                    for  var i   0  i  lt  count  i    index                        T item   Items index             if  match item                           Items RemoveAt index               removedCount                 if  clusterIndex    index                              Debug Assert cluster    null                 cluster Add item                             else                             cluster   new List lt T gt    item                  clusterIndex   index                             index--                        else if  clusterIndex  gt  -1                          OnCollectionChanged new NotifyCollectionChangedEventArgs NotifyCollectionChangedAction Remove  cluster  clusterIndex                clusterIndex   -1              cluster   null                                 if  clusterIndex  gt  -1            OnCollectionChanged new NotifyCollectionChangedEventArgs NotifyCollectionChangedAction Remove  cluster  clusterIndex                   if  removedCount  gt  0          OnEssentialPropertiesChanged           return removedCount                  lt summary gt          Removes a range of elements from the  lt see cref  ObservableCollection T    gt  gt            lt  summary gt           lt param name  index  gt The zero-based starting index of the range of elements to remove  lt  param gt           lt param name  count  gt The number of elements to remove  lt  param gt           lt exception cref  ArgumentOutOfRangeException  gt The specified range is exceeding the collection  lt  exception gt      public void RemoveRange int index  int count              if  index  lt  0          throw new ArgumentOutOfRangeException nameof index          if  count  lt  0          throw new ArgumentOutOfRangeException nameof count          if  index   count  gt  Count          throw new ArgumentOutOfRangeException nameof index           if  count    0          return         if  count    1                  RemoveItem index           return                   Items will always be List lt T gt   see constructors       var items    List lt T gt  Items        List lt T gt  removedItems   items GetRange index  count          CheckReentrancy           items RemoveRange index  count          OnEssentialPropertiesChanged           if  Count    0          OnCollectionReset          else         OnCollectionChanged new NotifyCollectionChangedEventArgs NotifyCollectionChangedAction Remove  removedItems  index                    lt summary gt           Clears the current collection and replaces it with the specified collection          using the default  lt see cref  EqualityComparer T    gt            lt  summary gt                        lt param name  collection  gt The items to fill the collection with  after clearing it  lt  param gt           lt exception cref  ArgumentNullException  gt  lt paramref name  collection   gt  is null  lt  exception gt      public void ReplaceRange IEnumerable lt T gt  collection              ReplaceRange 0  Count  collection  EqualityComparer lt T gt  Default                   lt summary gt          Clears the current collection and replaces it with the specified collection          using the specified comparer to skip equal items           lt  summary gt           lt param name  collection  gt The items to fill the collection with  after clearing it  lt  param gt           lt param name  comparer  gt An  lt see cref  IEqualityComparer T    gt  to be used         to check whether an item in the same location already existed before          which in case it would not be added to the collection  and no event will be raised for it  lt  param gt           lt exception cref  ArgumentNullException  gt  lt paramref name  collection   gt  is null  lt  exception gt           lt exception cref  ArgumentNullException  gt  lt paramref name  comparer   gt  is null  lt  exception gt      public void ReplaceRange IEnumerable lt T gt  collection  IEqualityComparer lt T gt  comparer              ReplaceRange 0  Count  collection  comparer                   lt summary gt          Removes the specified range and inserts the specified collection          ignoring equal items  using  lt see cref  EqualityComparer T  Default   gt             lt  summary gt           lt param name  index  gt The index of where to start the replacement  lt  param gt           lt param name  count  gt The number of items to be replaced  lt  param gt           lt param name  collection  gt The collection to insert in that location  lt  param gt           lt exception cref  ArgumentOutOfRangeException  gt  lt paramref name  index   gt  is out of range  lt  exception gt           lt exception cref  ArgumentOutOfRangeException  gt  lt paramref name  count   gt  is out of range  lt  exception gt           lt exception cref  ArgumentNullException  gt  lt paramref name  collection   gt  is null  lt  exception gt      public void ReplaceRange int index  int count  IEnumerable lt T gt  collection              ReplaceRange index  count  collection  EqualityComparer lt T gt  Default                   lt summary gt          Removes the specified range and inserts the specified collection in its position  leaving equal items in equal positions intact           lt  summary gt           lt param name  index  gt The index of where to start the replacement  lt  param gt           lt param name  count  gt The number of items to be replaced  lt  param gt           lt param name  collection  gt The collection to insert in that location  lt  param gt           lt param name  comparer  gt The comparer to use when checking for equal items  lt  param gt           lt exception cref  ArgumentOutOfRangeException  gt  lt paramref name  index   gt  is out of range  lt  exception gt           lt exception cref  ArgumentOutOfRangeException  gt  lt paramref name  count   gt  is out of range  lt  exception gt           lt exception cref  ArgumentNullException  gt  lt paramref name  collection   gt  is null  lt  exception gt           lt exception cref  ArgumentNullException  gt  lt paramref name  comparer   gt  is null  lt  exception gt      public void ReplaceRange int index  int count  IEnumerable lt T gt  collection  IEqualityComparer lt T gt  comparer              if  index  lt  0          throw new ArgumentOutOfRangeException nameof index          if  count  lt  0          throw new ArgumentOutOfRangeException nameof count          if  index   count  gt  Count          throw new ArgumentOutOfRangeException nameof index           if  collection    null          throw new ArgumentNullException nameof collection          if  comparer    null          throw new ArgumentNullException nameof comparer           if  collection is ICollection lt T gt  countable                  if  countable Count    0                      RemoveRange index  count             return                          else if   ContainsAny collection                   RemoveRange index  count           return                 if  index   count    0                  InsertRange 0  collection           return                 if    collection is IList lt T gt  list           list   new List lt T gt  collection          using  BlockReentrancy          using  DeferEvents                    var rangeCount   index   count          var addedCount   list Count           var changesMade   false          List lt T gt              newCluster   null              oldCluster   null            int i   index          for    i  lt  rangeCount  amp  amp  i - index  lt  addedCount  i                          parallel position           T old   this i    new   list i - index             if  comparer Equals old   new                           OnRangeReplaced i  newCluster  oldCluster               continue                        else                         Items i     new               if  newCluster    null                              Debug Assert oldCluster    null                 newCluster   new List lt T gt     new                  oldCluster   new List lt T gt    old                              else                             newCluster Add  new                 oldCluster Add old                              changesMade   true                                 OnRangeReplaced i  newCluster  oldCluster              exceeding position         if  count    addedCount                      var items    List lt T gt  Items            if  count  gt  addedCount                          var removedCount   rangeCount - addedCount              T   removed   new T removedCount               items CopyTo i  removed  0  removed Length               items RemoveRange i  removedCount               OnCollectionChanged new NotifyCollectionChangedEventArgs NotifyCollectionChangedAction Remove  removed  i                          else                         var k   i - index              T   added   new T addedCount - k               for  int j   k  j  lt  addedCount  j                                T  new   list j                 added j - k     new                            items InsertRange i  added               OnCollectionChanged new NotifyCollectionChangedEventArgs NotifyCollectionChangedAction Add  added  i                           OnEssentialPropertiesChanged                      else if  changesMade                      OnIndexerPropertyChanged                                  endregion Public Methods         ------------------------------------------------------                Protected Methods              ------------------------------------------------------       region Protected Methods           lt summary gt          Called by base class Collection amp lt T amp gt  when the list is being cleared          raises a CollectionChanged event to any listeners           lt  summary gt      protected override void ClearItems               if  Count    0          return         CheckReentrancy          base ClearItems          OnEssentialPropertiesChanged          OnCollectionReset                    lt summary gt          Called by base class Collection amp lt T amp gt  when an item is set in list          raises a CollectionChanged event to any listeners           lt  summary gt      protected override void SetItem int index  T item              if  Equals this index   item           return         CheckReentrancy          T originalItem   this index         base SetItem index  item          OnIndexerPropertyChanged          OnCollectionChanged NotifyCollectionChangedAction Replace  originalItem  item  index                   lt summary gt          Raise CollectionChanged event to any listeners          Properties methods modifying this ObservableCollection will raise         a collection changed event through this virtual method           lt  summary gt           lt remarks gt          When overriding this method  either call its base implementation         or call  lt see cref  BlockReentrancy   gt  to guard against reentrant collection changes           lt  remarks gt      protected override void OnCollectionChanged NotifyCollectionChangedEventArgs e              if   deferredEvents    null                   deferredEvents Add e           return                base OnCollectionChanged e              protected virtual IDisposable DeferEvents     gt  new DeferredEventsCollection this         endregion Protected Methods         ------------------------------------------------------                Private Methods              ------------------------------------------------------       region Private Methods           lt summary gt          Helper function to determine if a collection contains any elements           lt  summary gt           lt param name  collection  gt The collection to evaluate  lt  param gt           lt returns gt  lt  returns gt      private static bool ContainsAny IEnumerable lt T gt  collection              using  IEnumerator lt T gt  enumerator   collection GetEnumerator            return enumerator MoveNext                    lt summary gt          Helper to raise Count property and the Indexer property           lt  summary gt      private void OnEssentialPropertiesChanged               OnPropertyChanged EventArgsCache CountPropertyChanged         OnIndexerPropertyChanged                    lt summary gt              Helper to raise a PropertyChanged event for the Indexer property              lt  summary gt      private void OnIndexerPropertyChanged     gt        OnPropertyChanged EventArgsCache IndexerPropertyChanged             lt summary gt          Helper to raise CollectionChanged event to any listeners          lt  summary gt      private void OnCollectionChanged NotifyCollectionChangedAction action  object oldItem  object newItem  int index    gt        OnCollectionChanged new NotifyCollectionChangedEventArgs action  newItem  oldItem  index              lt summary gt          Helper to raise CollectionChanged event with action    Reset to any listeners          lt  summary gt      private void OnCollectionReset     gt        OnCollectionChanged EventArgsCache ResetCollectionChanged             lt summary gt          Helper to raise event for clustered action and clear cluster           lt  summary gt           lt param name  followingItemIndex  gt The index of the item following the replacement block  lt  param gt           lt param name  newCluster  gt  lt  param gt           lt param name  oldCluster  gt  lt  param gt        TODO should have really been a local method inside ReplaceRange int index  int count  IEnumerable lt T gt  collection  IEqualityComparer lt T gt  comparer         move when supported language version updated      private void OnRangeReplaced int followingItemIndex  ICollection lt T gt  newCluster  ICollection lt T gt  oldCluster              if  oldCluster    null    oldCluster Count    0                  Debug Assert newCluster    null    newCluster Count    0           return                 OnCollectionChanged            new NotifyCollectionChangedEventArgs                NotifyCollectionChangedAction Replace                new List lt T gt  newCluster                 new List lt T gt  oldCluster                 followingItemIndex - oldCluster Count           oldCluster Clear          newCluster Clear                endregion Private Methods        ------------------------------------------------------                Private Types              ------------------------------------------------------       region Private Types     private sealed class DeferredEventsCollection   List lt NotifyCollectionChangedEventArgs gt   IDisposable             private readonly ObservableRangeCollection lt T gt   collection        public DeferredEventsCollection ObservableRangeCollection lt T gt  collection                  Debug Assert collection    null           Debug Assert collection  deferredEvents    null            collection   collection           collection  deferredEvents   this                 public void Dispose                    collection  deferredEvents   null          foreach  var args in this             collection OnCollectionChanged args                       endregion Private Types              lt remarks gt        To be kept outside  lt see cref  ObservableCollection T    gt   since otherwise  a new instance will be created for each generic type used         lt  remarks gt    internal static class EventArgsCache         internal static readonly PropertyChangedEventArgs CountPropertyChanged   new PropertyChangedEventArgs  Count        internal static readonly PropertyChangedEventArgs IndexerPropertyChanged   new PropertyChangedEventArgs  Item          internal static readonly NotifyCollectionChangedEventArgs ResetCollectionChanged   new NotifyCollectionChangedEventArgs NotifyCollectionChangedAction Reset

[c#] ObservableCollection Doesn't support AddRange method, so I get notified for each item added, besides what about INotifyCollectionChanging?

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