Grid DevExpress in Xamarin.Forms (ask about new row, validation and picker column)

Hi to all. I'm new on xamarin world. I must create an app for Ios, and i must use on one my page two GridView. So i decide to use the DevExpress library. This is my code :

xaml :

    <dxGrid:GridControl x:Name="gridDet" ItemsSource="GoodItemsBuyed" NewItemRowVisibility="True" Grid.Row="9" Grid.Column="0" Grid.ColumnSpan="4" Grid.RowSpan="3" RowHeight="25" >
        <dxGrid:GridControl.Columns>
            <dxGrid:TextColumn FieldName="Description" Caption="Descrizione"></dxGrid:TextColumn>
            <dxGrid:NumberColumn FieldName="Qty" Caption="Qty"></dxGrid:NumberColumn>
            <dxGrid:PickerColumn FieldName="Vat" Caption="Vat Rate" ItemsSource="{Binding ListVatRate}"></dxGrid:PickerColumn>
            <dxGrid:NumberColumn FieldName="GrossAmount" Caption="Gross Amount"></dxGrid:NumberColumn>
        </dxGrid:GridControl.Columns>
    </dxGrid:GridControl>

.cs:

i've two property:

    public ObservableCollection<double> ListVatRate { get; set; }
    public ObservableCollection<GoodItemGridObject> GoodItemsBuyed { get; set; }

i've a Load() method that populate ListVatRate object, but when i tap new row, pickercolum is empty (i don't see nothing on it.. ). I read documentation about PickerColumn in devexpress site, but i don't understand what i wrong. I'm sure that ListVatRate is loaded, and i think is correct my xaml for binding for pickercolumn, but the code doesn't work (this is my first question).

My second question is about the moment when i add new row. I don't find an event associate, but i must to know the moment when user tap on "apply" button in the grid because i want to do a validation on data that user insert in the row ..and (this is my third question).. If all is well.. I should have a second grid starting from some of the data I put on the first one, but if I can not capture the moment of the ADD of the new line, I would not know how to trigger the logic of the second line.

Best Regards,
Nicola