WPF Combobox validation

Question

Hi. I have a ComboBox with Sex(male, female..):And I demand from user to select a value (the ComboBox has no value by default.)

<ComboBox ItemsSource="{x:Static Member=data:Sex.AllTypes}" SelectedItem="{Binding Path=Sex.Value, ValidatesOnDataErrors=True, UpdateSourceTrigger=PropertyChanged, NotifyOnValidationError=True}"  VerticalAlignment="Top">
        <ComboBox.ItemTemplate>
             <DataTemplate>
                  <StackPanel Orientation="Horizontal">
                      <TextBlock Text="{Binding Path=Name}" />
                  </StackPanel>
             </DataTemplate>
        </ComboBox.ItemTemplate>
</ComboBox>

Sex.Value is a Property in my Person class:

public class Person : IDataErrorInfo 
{
public string this[string columnName]
        {
            get
            {                
                switch (columnName)
                {                   
                    case "Sex": return Sex.Value == null ? "Required field" : null;
                    case "Surname": return string.IsNullOrEmpty(Nachname) ? "Required field" : null;
                }                
            }
        }
 public string Error
        {
            get
            {
                return null;
            }
        }
}

the problem is that it never enters this[string columnname].

When i try a TextBox with name, it enters this[string columnname] and everything works fine:

<TextBox  Style="{StaticResource textBoxInError}"   Text="{Binding Path=Surname, ValidatesOnDataErrors=True, UpdateSourceTrigger=PropertyChanged, NotifyOnValidationError=True}"/>

Answer 1

I've decided to do it this way:

When user clicks on Save, the validation occur. Then I simply check in a validation event, if a SelectedValue is null. If it's the case, then it means that the user didn't choose any of items. Then I warn him about this fact.

private void CanSave(object sender, CanExecuteRoutedEventArgs e)
{
    e.CanExecute = myComboBox.SelectedValue != null;
}

Answer 2

The good way in windows is to add a value (None) into the combobox and test if the person contains the (None) value. "(None)" is a meta-option because it is not a valid value for the choice—rather it describes that the option itself isn't being used.

Correct:

Incorrect:

The validation doesn't work in your case because no value is selected when you want to say that no sex is selected...