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I was trying to implement a specialized collection that works like ObservableCollection to encapsulate some more mechanisms in it, to do that i also let my collection inherit from Collection and i also implement the same interfaces.
I just do not get though how one actually implements the whole collection-changed-logic, for example Collection<T>.Add is not being overridden (it is not even marked as virtual), so how does the ObservableCollection fire the CollectionChanged event if items were added using that method?
458
By default, you can use Add method to add a single item into ObservableCollection . To add a range of items, you can call the Add method multiple times using foreach statement.
Add(new Item() { ItemId = 1 }); // Also works for (int i = 1; i < 10; i++) { Items. Add(new Item() { ItemId = i }); } });
An ObservableCollection is a dynamic collection of objects of a given type. Objects can be added, removed or be updated with an automatic notification of actions.
The true difference is rather straightforward: ObservableCollection<T> implements INotifyCollectionChanged which provides notification when the collection is changed (you guessed ^^) It allows the binding engine to update the UI when the ObservableCollection is updated. However, BindingList<T> implements IBindingList .
To answer your specific question, Collection<T>.Add calls the InsertItem virtual method (after checking that the collection is not read-only). ObservableCollection<T> indeed overrides this method to do the insert and raise the relevant change notifications.
144
It does so by calling InsertItem which is overridden and can be seen upon decompilation
protected override void InsertItem(int index, T item)
{
this.CheckReentrancy();
base.InsertItem(index, item);
this.OnPropertyChanged("Count");
this.OnPropertyChanged("Item[]");
this.OnCollectionChanged(NotifyCollectionChangedAction.Add, item, index);
}
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