How to Efficiently Notify an ObservableCollection of Item Property Changes?

How to Notify ObservableCollection When Item Changes

The ObservableCollection class in .NET provides a means to track changes to a collection, such as adding or removing items. However, it does not automatically detect changes to the properties of items within the collection.

To address this issue, custom implementations exist, such as the TrulyObservableCollection mentioned in the question. This class extends ObservableCollection and adds event handlers for items added and removed from the collection. It also tracks property changes on individual items.

Implementation and Usage

To use TrulyObservableCollection, you would first create an instance and populate it with items:

public class MyViewModel
{
    public TrulyObservableCollection<MyType> MyItemsSource { get; set; }

    public MyViewModel()
    {
        MyItemsSource = new TrulyObservableCollection<MyType>();
        MyItemsSource.Add(new MyType() { MyProperty = false });
        MyItemsSource.Add(new MyType() { MyProperty = true });
        MyItemsSource.Add(new MyType() { MyProperty = false });
    }
}

However, the implementation of TrulyObservableCollection raises a Reset event for the entire collection whenever an item property changes. This can have performance implications and may not be the desired behavior.

Alternative Approach

An alternative approach is to register property change event handlers for each item in the collection directly:

public class MyViewModel
{
    public ObservableCollection<MyType> MyItemsSource { get; set; }

    public MyViewModel()
    {
        MyItemsSource = new ObservableCollection<MyType>();
        MyItemsSource.CollectionChanged += MyItemsSource_CollectionChanged;

        MyItemsSource.Add(new MyType() { MyProperty = false });
        MyItemsSource.Add(new MyType() { MyProperty = true });
        MyItemsSource.Add(new MyType() { MyProperty = false });
    }

    private 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;
    }

    private void MyType_PropertyChanged(object sender, PropertyChangedEventArgs e)
    {
        if (e.PropertyName == "MyProperty")
            DoWork(); // Perform desired action
    }
}

By registering property change event handlers only for items when they are added or removed from the collection, this approach targets item property changes more effectively while avoiding performance overheads.

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