Friday, February 4, 2011

Is there an event that triggers if the number of ListViewItems in a ListView changes? (Windows Forms)

I'd like to enable/disable some other controls based on how many items are in my ListView control. I can't find any event that would do this, either on the ListView itself or on the ListViewItemCollection. Maybe there's a way to generically watch any collection in C# for changes?

I'd be happy with other events too, even ones that sometimes fire when the items don't change, but for example the ControlAdded and Layout events didn't work :(.

  • I can't find any events that you could use. Perhaps you could subclass ListViewItemCollection, and raise your own event when something is added, with code similar to this.

    Public Class MyListViewItemCollection
        Inherits ListView.ListViewItemCollection
        Public Event ItemAdded(ByVal Item As ListViewItem)
        Sub New(ByVal owner As ListView)
        End Sub
        Public Overrides Function Add(ByVal value As System.Windows.Forms.ListViewItem) As System.Windows.Forms.ListViewItem
            Dim Item As ListViewItem
            Item = MyBase.Add(value)
            RaiseEvent ItemAdded(Item)
            Return Item
        End Function
    End Class
    From Kibbee
  • @ Kibbee: OK, but then how would I get my ListView to use that collection internally?

    From Domenic
  • I think the best thing that you can do here is to subclass ListView and provide the events that you want.

    From John
  • @Domenic

    Not too sure, Never quite got that far in the thought process.

    Another solution might be to extend ListView, and when adding and removing stuff, instead of calling .items.add, and items.remove, you call your other functions. It would still be possible to add and remove without events being raised, but with a little code review to make sure .items.add and .items.remove weren't called directly, it could work out quite well. Here's a little example. I only showed 1 Add function, but there are 6 you would have to implement, if you wanted to have use of all the available add functions. There's also .AddRange, and .Clear that you might want to take a look at.

    Public Class MonitoredListView
        Inherits ListView
        Public Event ItemAdded()
        Public Event ItemRemoved()
        Public Sub New()
        End Sub
        Public Function AddItem(ByVal Text As String) As ListViewItem
            RaiseEvent ItemAdded()
        End Function
        Public Sub RemoveItem(ByVal Item As ListViewItem)
            RaiseEvent ItemRemoved()
        End Sub
    End Class
    From Kibbee


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