Using roles/permission to enable/disable content in the view

Question

I'm working on an WPF application using the mvvm-light framework. I'm new to both of these.

I have a form that allows a user to edit a record in a database. Admin users need to be able to update a field that should be read-only for other users. It would be easy for me to put this enable/disable code in the view's code-behind but my understanding is that this belongs in the ViewModel.

How do I hide this textbox without putting the code in the View?

Thanks in advance.

        <TextBox Grid.Column="1" Grid.Row="0" HorizontalAlignment="Left" Name="uxMallNum" VerticalAlignment="Center"
        Width="100" Height="25" MaxLength="50" Validation.ErrorTemplate="{DynamicResource validationTemplate}" Style="{DynamicResource textStyleTextBox}">
        <TextBox.Text>
            <Binding Path="MallNumber" UpdateSourceTrigger="PropertyChanged" Mode="TwoWay" >
                <Binding.ValidationRules>
                    <local:StringRangeValidationRule MinimumLength="1" MaximumLength="50" 
                                    ErrorMessage="Mall Number is required and must be 50 characters or fewer." />
                </Binding.ValidationRules>
            </Binding>
        </TextBox.Text>
    </TextBox>

Answer 1

I've built a converter for this type of function, although I'm not sure if there's a better way.

public class AdminVisibilityConverter : IValueConverter
{
    #region Methods
    public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
    {
        bool isAdmin = WebContext.Current.User.IsInRole("Admin");

        return isAdmin ? Visibility.Visible : Visibility.Collapsed;
    }

    public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture)
    {
        throw new NotImplementedException();
    }
    #endregion
}

Then I add the converter to the visibility property of a control.

<toolkit:AccordionItem Tag="#ManageAnnouncements" Visibility="{Binding Source=User, Converter={StaticResource AdminVisibilityConverter}}">

You could pass in the roles, or usernames, in the parameter of the converter, but my instance didn't need it.