How do I pass a property changed event to an ancestor?

Question

I'm sure I am missing some of the basics here so please bear with me.

I have a two objects, a SalesOrder and a SalesOrderLineItem. The lineitems are kept in an Observablecollection<SalesOrderLineItem> of SalesOrder, and if I add line items my databound listView knows about the new items.

Now where I am having a problem is here: The SalesOrder has a read only property called "OrderTotal", which knows what the total price from all the line items combined are.

If I change the quantity, or price of a line item, I don't seem to know how to get change notification to bubble up to "OrderTotal".

Both classes inherit from, and fire INotifyPropertyChanged.

Wham am I missing?

Answer 1

The ObservableCollection only notifies when an Item is added, removed, or when the list is refreshed, not when a property of an Item within the collection changes.

The SalesOrder class needs to be listening to each SalesOrderLineItem's PropertyChanged event.

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The OrderTotal property could also be dynamic, generating the total each time...

Answer 2

If you feel adventurous, you can try BindableLinq or something similar. It allows you to expose the result of a query that listens to changes.

But it's not out of beta yet, and I'm not sure it will ever be... ContinuousLinq is another one, but it does not support Silverlight at all yet.

Other than that, you'll have to listen to each child, and add/remove handlers whenever the collection changes.