.NET (Core and Framework)

Hello I have a combobox binding to a ObservableCollection of a table, where I fetch the ID field that deposit in another table, so everything is right, the problem arises when I want my ValidatesOnNotifyDataErrors doing its job, but it does the property in question is set to [Required] will post the code I hope you can help out:

Combobox:

<pre lang="xml"><ComboBox HorizontalAlignment="Left" Margin="327,116,0,0" VerticalAlignment="Top" Width="120" ItemsSource="{Binding NegozioObser}" SelectedItem="{Binding NegozioSelezionato, ValidatesOnNotifyDataErrors=True}">
                <ComboBox.ItemTemplate>
				<DataTemplate>
					<Grid>
						<TextBlock Text="{Binding RagioneSociale}"/>
					</Grid>
				</DataTemplate>
			</ComboBox.ItemTemplate>
		</ComboBox>

[Required]
        
        public int NegozioID 
        {
            get { return _NegozioID; }
            set { _NegozioID = value; RaisePropertyChanged("NegozioID"); }
        }

ObservableCollection<Negozio> _Negozios;

        public ObservableCollection<Negozio> NegozioObser
        {
            get { return _Negozios; }
            set
            {
                _Negozios = value;
                RaisePropertyChanged("NegozioObser");
            }
        }