Notify ObservableCollection when Item changes

Question

I found on this link   ObservableCollection not noticing when Item in it changes  even with INotifyPropertyChanged   some techniques to notify a Observablecollection that an item has changed  the TrulyObservableCollection in this link seems to be what i m looking for   public class TrulyObservableCollection lt T gt    ObservableCollection lt T gt  where T   INotifyPropertyChanged       public TrulyObservableCollection         base                 CollectionChanged    new NotifyCollectionChangedEventHandler TrulyObservableCollection CollectionChanged              void TrulyObservableCollection CollectionChanged object sender  NotifyCollectionChangedEventArgs e                if  e NewItems    null                        foreach  Object item in e NewItems                                 item as INotifyPropertyChanged  PropertyChanged    new PropertyChangedEventHandler item PropertyChanged                                   if  e OldItems    null                        foreach  Object item in e OldItems                                 item as INotifyPropertyChanged  PropertyChanged -  new PropertyChangedEventHandler item PropertyChanged                                      void item PropertyChanged object sender  PropertyChangedEventArgs e                NotifyCollectionChangedEventArgs a   new NotifyCollectionChangedEventArgs NotifyCollectionChangedAction Reset           OnCollectionChanged a             But when I try to use it  I don t get notifications on the collection  I m not sure how to correctly implement this in my C  Code   XAML         lt DataGrid AutoGenerateColumns  False  ItemsSource   Binding MyItemsSource  Mode TwoWay  UpdateSourceTrigger PropertyChanged   gt           lt DataGrid Columns gt               lt DataGridCheckBoxColumn Binding   Binding MyProperty  Mode TwoWay  UpdateSourceTrigger PropertyChanged    gt           lt  DataGrid Columns gt       lt  DataGrid gt    ViewModel    public class MyViewModel   ViewModelBase       private TrulyObservableCollection lt MyType gt  myItemsSource      public TrulyObservableCollection lt MyType gt  MyItemsSource               get   return myItemsSource            set                         myItemsSource   value                  Code to trig on item change                RaisePropertyChangedEvent  MyItemsSource                         public MyViewModel                 MyItemsSource   new TrulyObservableCollection lt MyType gt                           new MyType     MyProperty   false                new MyType     MyProperty   true                new MyType     MyProperty   false                       public class MyType   ViewModelBase       private bool myProperty      public bool MyProperty               get   return myProperty            set                        myProperty   value              RaisePropertyChangedEvent  MyProperty                       public class ViewModelBase   INotifyPropertyChanged       public event PropertyChangedEventHandler PropertyChanged       protected void RaisePropertyChangedEvent string propertyName                if  PropertyChanged    null                        PropertyChangedEventArgs e   new PropertyChangedEventArgs propertyName               PropertyChanged this  e                       When i run the program  i have the 3 checkbox to false  true  false as in the property initialisation  but when i change the state of one of the ckeckbox  the program go through item PropertyChanged but never in MyItemsSource Property code

User · Answer

One simple solution to this is to replace the item being changed in the ObservableCollection which notifies the collection of the changed item  In the sample code snippet below Artists is the ObservableCollection and artist is an item of the type in the ObservableCollection      var index   Artists IndexOf artist       Artists RemoveAt index       artist IsFollowed   true     change something in the item     Artists Insert index  artist

User · Answer

A simple solution is to use BindingList lt T gt  instead of ObservableCollection lt T gt    Indeed the BindingList relay item change notifications  So with a binding list  if the  item implements the interface INotifyPropertyChanged then you can simply get notifications using the ListChanged event   See also this SO answer

User · Answer

The spot you have commented as    Code to trig on item change    will only trigger when the collection object gets changed  such as when it gets set to a new object  or set to null   With your current implementation of TrulyObservableCollection  to handle the property changed events of your collection  register something to the CollectionChanged event of MyItemsSource  public MyViewModel         MyItemsSource   new TrulyObservableCollection lt MyType gt         MyItemsSource CollectionChanged    MyItemsSource CollectionChanged       MyItemsSource Add new MyType     MyProperty   false         MyItemsSource Add new MyType     MyProperty   true        MyItemsSource Add new MyType     MyProperty   false         void MyItemsSource CollectionChanged object sender  NotifyCollectionChangedEventArgs e           Handle here     Personally I really don t like this implementation  You are raising a CollectionChanged event that says the entire collection has been reset  anytime a property changes  Sure it ll make the UI update anytime an item in the collection changes  but I see that being bad on performance  and it doesn t seem to have a way to identify what property changed  which is one of the key pieces of information I usually need when doing something on PropertyChanged    I prefer using a regular ObservableCollection and just hooking up the PropertyChanged events to it s items on CollectionChanged  Providing your UI is bound correctly to the items in the ObservableCollection  you shouldn t need to tell the UI to update when a property on an item in the collection changes   public MyViewModel         MyItemsSource   new ObservableCollection lt MyType gt         MyItemsSource CollectionChanged    MyItemsSource CollectionChanged       MyItemsSource Add new MyType     MyProperty   false         MyItemsSource Add new MyType     MyProperty   true        MyItemsSource Add new MyType     MyProperty   false        void MyItemsSource CollectionChanged object sender  NotifyCollectionChangedEventArgs e        if  e NewItems    null          foreach MyType item in e NewItems              item PropertyChanged    MyType PropertyChanged       if  e OldItems    null          foreach MyType item in e OldItems              item PropertyChanged -  MyType PropertyChanged     void MyType PropertyChanged object sender  PropertyChangedEventArgs e        if  e PropertyName     MyProperty           DoWork

User · Answer

I solved this case by using static Action     public class CatalogoModel        private String  Id      private String  Descripcion      private Boolean  IsChecked       public String Id               get   return  Id            set    Id   value              public String Descripcion               get   return  Descripcion            set    Descripcion   value              public Boolean IsChecked               get   return  IsChecked            set                       IsChecked   value              NotifyPropertyChanged  IsChecked                OnItemChecked Invoke                         public static Action OnItemChecked      public class ReglaViewModel   ViewModelBase       private ObservableCollection lt CatalogoModel gt   origenes       CatalogoModel OnItemChecked        gt                                var x   Origenes Count     Entra cada vez que cambia algo en  origenes

User · Answer

I know it s late  but maybe this helps others  I have created a class NotifyObservableCollection  that solves the problem of missing notification to item itself  when a property of the item changes  The usage is as simple as ObservableCollection   public class NotifyObservableCollection lt T gt    ObservableCollection lt T gt  where T   INotifyPropertyChanged       private void Handle object sender  PropertyChangedEventArgs args                OnCollectionChanged new NotifyCollectionChangedEventArgs NotifyCollectionChangedAction Reset  null               protected override void OnCollectionChanged NotifyCollectionChangedEventArgs e                if  e NewItems    null                foreach  object t in e NewItems                      T  t  PropertyChanged    Handle                                  if  e OldItems    null                foreach  object t in e OldItems                      T  t  PropertyChanged -  Handle                                  base OnCollectionChanged e           While Items are added or removed the class forwards the items PropertyChanged event to the collections PropertyChanged event   usage   public abstract class ParameterBase   INotifyPropertyChanged       protected readonly CultureInfo Ci   new CultureInfo  en-US        private string  value       public string Value           get   return  value            set               if  value     value  return               value   value              OnPropertyChanged                       public class AItem       public NotifyObservableCollection lt ParameterBase gt  Parameters           get   return  parameters            set               NotifyCollectionChangedEventHandler cceh    sender  args    gt  OnPropertyChanged                if   parameters    null   parameters CollectionChanged -  cceh               parameters   value                needed for Binding to AItem at xaml directly              parameters CollectionChanged    cceh                        public NotifyObservableCollection lt ParameterBase gt  DefaultParameters           get   return  defaultParameters            set               NotifyCollectionChangedEventHandler cceh    sender  args    gt  OnPropertyChanged                if   defaultParameters    null   defaultParameters CollectionChanged -  cceh               defaultParameters   value                needed for Binding to AItem at xaml directly              defaultParameters CollectionChanged    cceh                    public class MyViewModel       public NotifyObservableCollection lt AItem gt  DataItems   get  set        If now a property of an item in DataItems changes  the following xaml will get a notification  though it binds to Parameters 0  or to the item itself except to the changing property Value of the item  Converters at Triggers are called reliable on every change     lt DataGrid CanUserAddRows  False  AutoGenerateColumns  False  ItemsSource   Binding DataItems   gt       lt DataGrid Columns gt           lt DataGridTextColumn Binding   Binding Parameters 0  Value   Header  P1  gt               lt DataGridTextColumn CellStyle gt                   lt Style TargetType  DataGridCell  gt                       lt Setter Property  Background  Value  Aqua    gt                       lt Style Triggers gt                           lt DataTrigger Value  False  gt                               lt  -- Bind to Items with changing properties -- gt                               lt DataTrigger Binding gt                                   lt MultiBinding Converter   StaticResource ParameterCompareConverter   gt                                       lt Binding Path  DefaultParameters 0     gt                                       lt Binding Path  Parameters 0     gt                                   lt  MultiBinding gt                               lt  DataTrigger Binding gt                               lt Setter Property  Background  Value  DeepPink    gt                           lt  DataTrigger gt                           lt  -- Binds to AItem directly -- gt                           lt DataTrigger Value  True  Binding   Binding Converter  StaticResource CheckParametersConverter    gt                               lt Setter Property  FontWeight  Value  ExtraBold    gt                           lt  DataTrigger gt                       lt  Style Triggers gt                   lt  Style gt               lt  DataGridTextColumn CellStyle gt           lt  DataGridTextColumn gt

User · Answer

The ObservableCollection and its derivatives raises its property changes internally  The code in your setter should only be triggered if you assign a new TrulyObservableCollection lt MyType gt  to the MyItemsSource property  That is  it should only happen once  from the constructor   From that point forward  you ll get property change notifications from the collection  not from the setter in your viewmodel

User · Answer

All the solutions here are correct but they are missing an important scenario in which the method Clear   is used  which doesn t provide OldItems in the NotifyCollectionChangedEventArgs object   this is the perfect ObservableCollection    public delegate void ListedItemPropertyChangedEventHandler IList SourceList  object Item  PropertyChangedEventArgs e   public class ObservableCollectionEX lt T gt    ObservableCollection lt T gt         region Constructors     public ObservableCollectionEX     base                 CollectionChanged    ObservableCollection CollectionChanged            public ObservableCollectionEX IEnumerable lt T gt  c    base c                CollectionChanged    ObservableCollection CollectionChanged            public ObservableCollectionEX List lt T gt  l    base l                CollectionChanged    ObservableCollection CollectionChanged              endregion        public new void Clear                 foreach  var item in this                          if  item is INotifyPropertyChanged i                                  i PropertyChanged -  Element PropertyChanged                      base Clear              private void ObservableCollection CollectionChanged object sender  NotifyCollectionChangedEventArgs e                if  e OldItems    null              foreach  var item in e OldItems                                  if  item    null  amp  amp  item is INotifyPropertyChanged i                                          i PropertyChanged -  Element PropertyChanged            if  e NewItems    null              foreach  var item in e NewItems                                  if  item    null  amp  amp  item is INotifyPropertyChanged i                                        i PropertyChanged -  Element PropertyChanged                      i PropertyChanged    Element PropertyChanged                                            private void Element PropertyChanged object sender  PropertyChangedEventArgs e    gt  ItemPropertyChanged  Invoke this  sender  e         public ListedItemPropertyChangedEventHandler ItemPropertyChanged

User · Answer

You could use an extension method to get notified about changed property of an item in a collection in a generic way   public static class ObservableCollectionExtension       public static void NotifyPropertyChanged lt T gt  this ObservableCollection lt T gt  observableCollection  Action lt T  PropertyChangedEventArgs gt  callBackAction          where T   INotifyPropertyChanged               observableCollection CollectionChanged     sender  args    gt                          Does not prevent garbage collection says  http   stackoverflow com questions 298261 do-event-handlers-stop-garbage-collection-from-occuring               publisher SomeEvent    target SomeHandler                then  publisher  will keep  target  alive  but  target  will not keep  publisher  alive              if  args NewItems    null  return              foreach  T item in args NewItems                                item PropertyChanged     obj  eventArgs    gt                                        callBackAction  T obj  eventArgs                                                        public void ExampleUsage         var myObservableCollection   new ObservableCollection lt MyTypeWithNotifyPropertyChanged gt         myObservableCollection NotifyPropertyChanged  obj  notifyPropertyChangedEventArgs    gt                  DO here what you want when a property of an item in the collection has changed

[c#] Notify ObservableCollection when Item changes

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