How to Make ObservableCollection Notify When Item Properties Change?

Notify ObservableCollection When Item Changes

ObservableCollection is a handy collection type that implements INotifyCollectionChanged interface, which allows you to listen for changes in the collection. However, ObservableCollection does not notify about changes made to properties of the items within the collection.

Overcoming the Limitation

To address this limitation, you can implement a custom ObservableCollection called TrulyObservableCollection, which inherits from ObservableCollection and overrides the CollectionChanged event handler to subscribe and unsubscribe to the PropertyChanged event of items added and removed from the collection.

TrulyObservableCollection

public class TrulyObservableCollection<T> : ObservableCollection<T>
where T : INotifyPropertyChanged
{
    public TrulyObservableCollection()
        : base()
    {
        CollectionChanged += 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);
    }
}

Usage

To use TrulyObservableCollection, simply replace ObservableCollection with TrulyObservableCollection in your code. You need to attach handlers to the CollectionChanged event of the collection to handle changes.

MyItemsSource = new TrulyObservableCollection<MyType>();
MyItemsSource.CollectionChanged += MyItemsSource_CollectionChanged;

Within the CollectionChanged event handler, you can subscribe to or unsubscribe from the PropertyChanged events of items added and removed from the collection.

void MyItemsSource_CollectionChanged(object sender, NotifyCollectionChangedEventArgs e)
{
    if (e.NewItems != null)
        foreach (MyType item in e.NewItems)
            item.PropertyChanged += new PropertyChangedEventHandler(MyType_PropertyChanged);

    if (e.OldItems != null)
        foreach (MyType item in e.OldItems)
            item.PropertyChanged -= new PropertyChangedEventHandler(MyType_PropertyChanged);
}

Alternative Approach

While TrulyObservableCollection allows you to force collection change notifications, it may not be the most optimal approach. A more common pattern is to handle PropertyChanged events of individual items within the CollectionChanged handler of ObservableCollection. This ensures that only specific property changes within the collection cause UI updates, optimizing performance and providing more granular control.

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