Event when child added to list

Event when child added to list

Old forum URL: forums.lhotka.net/forums/t/7850.aspx

Fele posted on Thursday, October 22, 2009

Does Csla raise event when a new child is added to list of children?

Thanks
Fele

RockfordLhotka replied on Thursday, October 22, 2009

Yes, this is a standard behavior of .NET collections like BindingList<T> (which is the base class for all CSLA lists). The event is called ListChanged.

On Silverlight the base class is ObservableCollection<T> and the event is called CollectionChanged.

RockfordLhotka replied on Thursday, October 22, 2009

Oh, also...

If you have an object structure like OrderEdit -> LineItems -> LineItem

and if you want code in OrderEdit to know that a new item was added to the list, your easiest option is to override OnChildChanged() - don't mess with events at all because they require hooking and unhooking and rehooking, where an override is just a lot simpler.

Fele replied on Thursday, October 22, 2009

Ok. I see it.
OnChildChanged was risen  but I can't figure out how to find out if it is adding, deleting or updating child.


Thanks

Fele replied on Thursday, October 22, 2009

I will appreciate if you let me know if this is correct approach.

      protected override void OnChildChanged(ChildChangedEventArgs e)
        {
            base.OnChildChanged(e);
            if (e.PropertyChangedArgs != null)
            {
                switch (e.PropertyChangedArgs.PropertyName)
                {
                    case "X1":
                        CalcTotalAmt();
                        break;
                    default:
                        break;
                }
            }
            else
            {
                if (e.ChildObject.ToString() == "ObjectList")
                {
                    //check if added
                    if (e.ListChangedArgs.ListChangedType == ListChangedType.ItemAdded)
                    {
                        UpdateOtherObj();
                    }
                }
            }
        }

Only problem that I have my client classes linked to server ones and ListChangeType generate two errors:
1)'System.Collections.Specialized.NotifyCollectionChangedEventArgs' does not contain a definition for 'ListChangedType' and no extension method 'ListChangedType' accepting a first argument of type 'System.Collections.Specialized.NotifyCollectionChangedEventArgs' could be found (are you missing a using directive or an assembly reference?)   
2) The name 'ListChangedType' does not exist in the current context  

If I open this class on server side, it is OK.
On Client, I'm getting above errors.



RockfordLhotka replied on Thursday, October 22, 2009

Yes, that’s basically the idea – use the properties of ChildChangedEventArgs to determine what happened to what object.

 

I realize there are differences between SL and .NET – that’s because collections aren’t the same on the two platforms. The easiest answer is probably to use compiler directives to handle the different events on each side.

 

#if SILVERLIGHT

#else

#endif

 

Fele replied on Friday, October 23, 2009

Thanks for response.

If I correctly understood your last post, I should handle different events on client and server.
From my testing, I figured out that I can use OnChildChanged on server. I'm not sure which event I should handle on client.

If you can provide short  code example, I will appreciate.

Thanks
Fele

RockfordLhotka replied on Friday, October 23, 2009

You can override OnChildChanged() on client and server. What I am saying is that inside that override you’ll need to treat the ‘e’ parameter differently because on the server it will contain the ListChanged event args and on the client it will contain the CollectionChanged event args:

 

protected override void OnChildChanged(…)

{

#if SILVERLIGHT

  // use CollectionChanged event args

#else

  // use ListChanged event args

#endif

}

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