WPF ListView with ItemsSource: how to know when model adds item - wpf

Question

Question: What is "proper" way of letting the user control's "view model" (.xaml.cs file) know that a ListViewItem has been added to a ListView? Note that this post is addresses a different problem.
Details:
I have a UserControl which contains a ListView and a DataContext:
The ListView has an ItemsSource={Binding ActionLogEntries}
ActionLogEntries is an ObservableCollection property in the DataContext
The data context adds items to the ListView when certain things happen.
But there isn't a ListView.ItemAdded event. There is a CollectionChanged event on ObservableCollection in data context but the view model's handler of this event could get called before the item is added to the ListView so this doesn't seem like a good strategy.
FYI: This came up because when items are added to the ListView, it doesn't automatically scroll to the newly added item, which is behavior I have to add. Presumably I'd use ScrollIntoView after that.

Answer 1

So there are at least two ways of skinning this cat:
do as explained by Clemens in comment to my question
do as in this post by WPF Mentor
Solution 1 seems more natural for the event subscription, since you don't need to cast; also IntelliSense doesn't show class members of implemented interfaces without cast, so for Solution 2 you have to remember to look at what interfaces are implemented and check for events there too. Here is what the subscription looks like for each solution:
protected override void OnInitialized(EventArgs e)
{
base.OnInitialized(e);
// Solution 1, subscription:
xActionListView.ItemContainerGenerator.ItemsChanged +=
new ItemsChangedEventHandler(ActionLog_ItemsChanged);
// Solution 2, subscription:
((INotifyCollectionChanged)xActionListView.Items).CollectionChanged +=
new NotifyCollectionChangedEventHandler(ActionListView_CollectionChanged);
}
But solution 2 has easier to use event arg in handler:
// Solution 1, handler:
private void ActionLog_ItemsChanged(object sender, ItemsChangedEventArgs e)
{
if (e.Action == NotifyCollectionChangedAction.Add)
{
// Solution 1, scroll the new item into view
xActionListView.ScrollIntoView(
xActionListView.Items[e.Position.Index + e.Position.Offset]);
}
}
// Solution 2, handler:
private void ActionListView_CollectionChanged(
object sender, NotifyCollectionChangedEventArgs e)
{
if (e.Action == NotifyCollectionChangedAction.Add)
{
// Solution 2, scroll the new item into view
xActionListView.ScrollIntoView(e.NewItems[0]);
}
}
It looks like in some circumstances, one solution may be more appropriate than the other: the event data may be easier to use in one or the other based on what data you need.