WPF

Dispatcher.Invoke(new Action(()=>{collection.Add(element}));

class MElementsCollection :ObservableCollection<MElement>
    {
        #region Variables
        private Dispatcher mainDipatcher;

        public Dispatcher MainDipatcher
        {
            get {
                if (mainDipatcher == null)
                    mainDipatcher = App.MainDispatcher;
                return mainDipatcher; 
            }
        }
        #endregion

        public void AddThreadSafe(MElement mElement)
        {
            if (Thread.CurrentThread != MainDipatcher.Thread)
            {                
                    MainDipatcher.Invoke(new Action(() =>
                        {
                            this.Add(mElement);
                        }));
                
            }
            else
                this.Add(mElement);
        }
    }