Question

In my class I’ve got an ObservableCollection and I’m listening to its CollectionChanged event.
Thing is when I do Fou.ButtonData = an ObservableCollection variable , CollectionChanged event is never called and CreateButtons() never happens.
How can I make this work?

Thanks

The code

class Fou
{
   private ObservableCollection<string> buttonData; 
    public ObservableCollection<string> ButtonData
    {
        get { return buttonData; }
        set { buttonData = value; }
    }

   public Fou()
   {
       buttonData = new ObservableCollection<string>();
        buttonData.CollectionChanged += new System.Collections.Specialized.NotifyCollectionChangedEventHandler(buttonData_CollectionChanged);

   }

   void buttonData_CollectionChanged(object sender, System.Collections.Specialized.NotifyCollectionChangedEventArgs e)
    {
        CreateButtons();
    }
   }

Answer 1

From the code sample it looks like the event is never raised because the ObservableCollection<string> is never actually changed. It is created, it’s event assigned to and never actually modified after that. Is there some other code which modifies the collection.

Additionally there is a bug in the setter of ButtonData. You are allowing another piece of code to change the ObservableCollection<string> but you are not listening to it’s CollectionChanged event nor are you disconnecting from the previous one. I would make this a readonly property or change it to the following

public ObservableCollection<string> ButtonData
{
  get { return buttonData; }
  set 
  { 
    if (buttonData != null) {
      buttonData.CollectionChanged -= buttonData_CollectionChanged;
    }
    buttonData = value;
    if (buttonData != null) {
      buttonData.CollectionChanged += buttonData_CollectionChanged;
    }
  }
}