Property setter in binding called twice

Question

In order to try to be generic I implemented that WPF and C# Binding in the view but the problem is that the setter of the Value property in the Item class is called two times successively (without passing in any other function - I checked the call stack)

I don't really know if it's a problem of binding or a problem in the code but If you have any idea I would like to hear your feedback.

---

<DataGrid Grid.Row="1" ItemsSource="{Binding Questions}" AutoGenerateColumns="False" SelectedItem="{Binding Path=DataContext.Answer.QuestionItem, RelativeSource={RelativeSource AncestorType=UserControl}}" >
    <DataGrid.Columns>
        <DataGridTemplateColumn Header="Questions" Width="SizeTocells" IsReadOnly="True">
            <DataGridTemplateColumn.CellTemplate>
                <DataTemplate>
                    <TextBlock Text="{Binding Question}"></TextBlock>
                </DataTemplate>
            </DataGridTemplateColumn.CellTemplate>
        </DataGridTemplateColumn>
        <DataGridTemplateColumn Header="Answers" Width="SizeToCells" IsReadOnly="True">
            <DataGridTemplateColumn.CellTemplate>
                <DataTemplate>
                    <StackPanel Orientation="Horizontal" VerticalAlignment="Center" >
                        <ListView ItemsSource="{Binding Path=DataContext.Answer.Answers, Mode=OneWay, RelativeSource={RelativeSource AncestorType=UserControl}}">
                            <ListView.ItemTemplate>
                                <DataTemplate>
                                    <RadioButton GroupName="{Binding Path=GroupName, Mode=OneWay}" Content="{Binding Path=Content, Mode=OneWay}" IsChecked="{Binding Path=Value, Mode=TwoWay}" Margin="0, 0, 10, 0" />
                                </DataTemplate>
                            </ListView.ItemTemplate>
                        </ListView>
                    </StackPanel>
                </DataTemplate>
            </DataGridTemplateColumn.CellTemplate>
        </DataGridTemplateColumn>
    </DataGrid.Columns>
</DataGrid>

---

public class Item : BindableBase
{
    public string Content { get; }
    public string GroupName { get; }

    private bool _val;
    public bool Value
    {
        get { return _val; }
        set
        {
            SetProperty(ref _val, value);
        }
    }

    public Item(string content, string groupName, bool value = false)
    {
        Content = content;
        GroupName = groupName;
        Value = value;
    }
}

---

 public class AnswerModel
 {
        public List<Item> Answers { get; }

        public AnswerModel(List<string> possibleAnswers)
        {
            Answers = new List<Item>();
            for (int i = 0; i < possibleAnswers.Count(); ++i)
            {
                char c = Convert.ToChar('A' + i);
                var letter = Convert.ToString(c);
                Answers.Add(new Item(letter, "group" + letter));
            }
        }

 }

---

public class InsertWordQuestionViewModel : BindableBase, INavigationAware
{
    public AnswerModel Answer { get; private set; }

    public void OnNavigatedTo(NavigationContext navigationContext)
    {
        PossibleAnswers = new List<string>() { "A test", "B test2", "C test3"};
        Questions = navigationContext.Parameters["questions"] as List<QuestionModel<string, string>>;
        Answer = new AnswerModel(PossibleAnswers);
     }
 }

Answer 1

Value property in the Item class is called two times successively - I guess it happens in different items: one item/RadioButton gets unchecked, and another item/RadioButton gets checked. so value argument should be different for those two consequtive invocations