Javascript Observable collection count

I'm, accessing Silverlight ObservableCollection count in javascript, but I get the following error.,

Microsoft JScript runtime error: System.FormatException: Input string was not in a correct format.
   at System.Number.StringToNumber(String str, NumberStyles options, NumberBuffer& number, NumberFormatInfo info, Boolean parseDecimal)
   at System.Number.ParseInt32(String s, NumberStyles style, NumberFormatInfo info)
   at System.String.System.IConvertible.ToInt32(IFormatProvider provide开发者_JS百科r)
   at System.Convert.ChangeType(Object value, Type conversionType, IFormatProvider provider)
   at System.Windows.Hosting.ScriptingInterface.GetScriptParamValueForType(ScriptParam scriptParam, Type desiredType)
   at System.Windows.Hosting.ScriptingInterface.ConvertFromScriptParams(Type[] desiredTypes, ScriptParam[] args)
   at System.Windows.Browser.ManagedObjectInfo.ListIndexerMember.Invoke(ManagedObject obj, InvokeType invokeType, ScriptParam[] args)
   at System.Windows.Browser.ManagedObjectInfo.Invoke(ManagedObject obj, InvokeType invokeType, String memberName, ScriptParam[] args)
   at System.Windows.Hosting.ManagedHost.InvokeScriptableMember(IntPtr pHandle, Int32 nMemberID, Int32 nInvokeType, Int32 nArgCount, ScriptParam[] pArgs, ScriptParam& pResult, ExceptionInfo& pExcepInfo)

I'm using following code, where children is a observablecollection of custom object.,

            reg.OnDropping = function (sender, args) {
                if (args.toItem.Children.Count > 0) {
                    args.cancel = true;
                }
                else {
                    args.cancel = false;
                }
            }

Is there any other way to access the count in Javascript?

Regards, Karthik

In order to access a property of an object from Javascript either the property needs to be marked with the ScriptableMember attribute or the class to which it belongs is marked as ScriptableType. Neither of these is true of the ObservableCollection<T> class.

A pragmatic solution would be to add a HasChildren property to your Custom object:-

 [ScriptableMember]
 public bool HasChildren
 {
      get { return Children.Count > 0; }
 }

Have you made that observablecollection ScriptableMember? You need to add this attribute to make in available in javascript. Check the following link for more information:

Walkthrough: Calling Managed Code from JavaScript

HtmlPage.RegisterScriptableObject Method

I hope it helps.