Why Doesn't My ObservableCollection Notify on Item Changes, and How Can I Fix It?

Why Doesn't Notify ObservableCollection Work with Item Changes?

While searching for a solution to notify an ObservableCollection when an item changes, you stumbled upon TrulyObservableCollection, which is designed to address this specific issue. However, after implementing this class in your project, you realized that the collection notifications are not being triggered.

Upon investigating, it becomes apparent that the source of the problem lies in the MyItemsSource property in your MyViewModel class. While you have implemented the INotifyPropertyChanged interface, you have not included the necessary code to trigger the property change event. Specifically, you are missing the code that would call RaisePropertyChangedEvent("MyItemsSource") when the collection is changed.

To resolve this issue, you could add the following line to the setter of the MyItemsSource property:

private TrulyObservableCollection<MyType> myItemsSource;
public TrulyObservableCollection<MyType> MyItemsSource
{
    get { return myItemsSource; }
    set 
    { 
        myItemsSource = value; 
        // Code to trig on item change...
        RaisePropertyChangedEvent("MyItemsSource");
    }
}

However, this approach is not recommended as it will trigger the property change event whenever the collection is changed, regardless of whether it is due to an item change or some other change.

An alternative and more efficient approach is to use the CollectionChanged event of the TrulyObservableCollection to register a handler for the PropertyChanged event of each item in the collection. This way, you can selectively handle property changes for individual items rather than triggering a reset for the entire collection.

The following code snippet illustrates this approach:

public MyViewModel()
{
    MyItemsSource = new TrulyObservableCollection<MyType>();
    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
}

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