C# 带值转换器的IDataErrorInfo

我有点做错了，但我想不出来：

我有一个这样的模型：

public class Person : IDataErrorInfo {
  public DateTime Birthdate {
    get { return _birthdate; }
    set {
      if (!Valid(value))
        AddError("Birthdate", "Birthdate not valid");

      _birthdate = value;
    }
  }
}

public class DateToStringConverter : IValueConverter {
  public object Convert(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture) {
    return date.Date.ToShortDateString();
  }

  public object ConvertBack(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture) {
    DateTime result;

    if (DateTime.TryParse(text, out result))
    {
      return result;
    }

    return DependencyProperty.UnsetValue;
  }
}

<TextBox Text="{Binding Person.Birthdate,
                        Mode=TwoWay,
                        Converter={StaticResource DateToStringConverter},
                        ValidatesOnDataErrors=True}" />

像这样的值转换器：

public class Person : IDataErrorInfo {
  public DateTime Birthdate {
    get { return _birthdate; }
    set {
      if (!Valid(value))
        AddError("Birthdate", "Birthdate not valid");

      _birthdate = value;
    }
  }
}

public class DateToStringConverter : IValueConverter {
  public object Convert(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture) {
    return date.Date.ToShortDateString();
  }

  public object ConvertBack(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture) {
    DateTime result;

    if (DateTime.TryParse(text, out result))
    {
      return result;
    }

    return DependencyProperty.UnsetValue;
  }
}

<TextBox Text="{Binding Person.Birthdate,
                        Mode=TwoWay,
                        Converter={StaticResource DateToStringConverter},
                        ValidatesOnDataErrors=True}" />

还有这样一种观点：

public class Person : IDataErrorInfo {
  public DateTime Birthdate {
    get { return _birthdate; }
    set {
      if (!Valid(value))
        AddError("Birthdate", "Birthdate not valid");

      _birthdate = value;
    }
  }
}

public class DateToStringConverter : IValueConverter {
  public object Convert(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture) {
    return date.Date.ToShortDateString();
  }

  public object ConvertBack(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture) {
    DateTime result;

    if (DateTime.TryParse(text, out result))
    {
      return result;
    }

    return DependencyProperty.UnsetValue;
  }
}

<TextBox Text="{Binding Person.Birthdate,
                        Mode=TwoWay,
                        Converter={StaticResource DateToStringConverter},
                        ValidatesOnDataErrors=True}" />

---

如果有人将有效日期（如“1.1.1950”）修改为无效日期（如“1.1.abc”），则该值不会传递给此人，也不会使其无效。但生日文本框周围会显示一个红色边框。如何保留无效文本（由用户修改）并为IDataErrorInfo注册错误？

setter中是否应该有else语句？如果（！Valid（value）…else _birth=value；否，为什么？从外部调用集合，我认为它应该真正设置值（或抛出ArgumentException）。如果值无效，则对象处于无效状态。忽略设置将使对象处于有效状态-但使用旧值。我认为这是错误的。