如何数据绑定到RadioButton属性？

Question

我有一个使用MVVMLight的WPF应用程序。

我正在尝试在我的UI数据输入表单中绑定一个单选按钮。下面的XAML用于绑定到单选按钮，当我编辑并首次显示表单时，选中正确的单选按钮。但是当我去保存更改时，MySelectedItem.ItemID不会更新。

如何让选定的单选按钮更新MySelectedItem？

//View
<StackPanel 
Grid.Row="3" 
Grid.Column="1"
Orientation="Horizontal"
Margin="2,5,2,24" Grid.RowSpan="2">
<RadioButton 
    GroupName="MyGroup"
    Margin="4"
    IsChecked="{Binding Path=MySelectedItem.ItemID, 
        Mode=TwoWay, 
        Converter={StaticResource App_RadioBoolToIntConverter}, 
        ConverterParameter=2}" 
        Content="Choice 1"/>
<RadioButton 
    GroupName="MyGroup"
    Margin="4"
    IsChecked="{Binding Path=MySelectedItem.ItemID, 
        Mode=TwoWay, 
        Converter={StaticResource App_RadioBoolToIntConverter}, 
        ConverterParameter=1}" 
        Content="Choice 2"/>
</StackPanel>

//View Model
public const string MySelectedItemPropertyName = "MySelectedItem";

private MyModelObject _MySelectedItem = null;

/// <summary>
/// Sets and gets the MySelectedItem property.
/// Changes to that property's value raise the PropertyChanged event. 
/// </summary>
public MyModelObject MySelectedItem
{
    get
    {
        return _MySelectedItem;
    }
    set
    {
        if (_MySelectedItem == value)
        {
            return;
        }
        RaisePropertyChanging(MySelectedItemPropertyName);
        _MySelectedItem = value;
        RaisePropertyChanged(MySelectedItemPropertyName);
    }
}


//Converter App_RadioBoolToIntConverter
    public class RadioBoolToIntConverter : System.Windows.Data.IValueConverter
    {
        public object Convert(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
        {
            int integer = (int)value;
            if (integer == int.Parse(parameter.ToString()))
                return true;
            else
                return false;
        }

        public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture)
        {
            return parameter;
        }

    }