WPF underline binding (MVVM) - wpf

Question

Is there a way to bind underline?? I'm trying to achieve the following:
I have VievModel with a bool property:
public bool HomeButtonUnderline { get; set; } = false;
I would then like to control this property in the following function:
public void Home() {
//CurrentPage = ApplicationPage.Home;
//HomeButtonForeground = new SolidColorBrush(Colors.White);
HomeButtonUnderline = true;
SettingsButtonUnderline = false;
}
I could then utilize this control in XAML:
<Button>
<TextBlock Command="{Binding HomeNavCommand}" Underline="{Binding HomeButtonUnderline}"/>
</Button>
The problem is that there isn't an 'Underline' property, instead it is handled by 'TextDecorations':
<Button>
<TextBlock TextDecorations="Underline">
</Button>
So is there a way to control underline using MVVM or even without it??

Answer 1

You may use a DataTrigger in a Style for the TextBlock:
<Button Command="{Binding HomeNavCommand}">
<TextBlock Text="Home">
<TextBlock.Style>
<Style TargetType="TextBlock">
<Style.Triggers>
<DataTrigger Binding="{Binding HomeButtonUnderline}" Value="True">
<Setter Property="TextDecorations" Value="Underline"/>
</DataTrigger>
</Style.Triggers>
</Style>
</TextBlock.Style>
</TextBlock>
</Button>

Answer 2

Use a Converter to convert your model types (in this case, a bool) to the UI types (in this case, a TextDecoration).
public class UnderlineConverter : IValueConverter
{
public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
{
if (value == null)
return null;
return System.Convert.ToBoolean(value) ? TextDecorations.Underline : null;
}
public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture)
{
throw new NotSupportedException();
}
}
And then use it in your binding (after creating a resource in your Window, UserControl App.xaml or whereever you feel is the right place; for this sample I'm just putting it in the button resources)
<Button Command="{Binding HomeNavCommand}">
<Button.Resources>
<local:UnderlineConverter x:Key="UnderlineConverter" />
</Button.Resources>
<TextBlock TextDecorations="{Binding HomeButtonUnderline, Converter={StaticResource UnderlineConverter}"/>
</Button>

Answer 3

Of course, another way to handle this is for your view model to be the right type for the view:
public TextDecorationCollection HomeButtonUnderline { get; set; }
HomeButtonUnderline is already GUI-orientated, so there's probably some code in your viewmodel that assigns a value from the model, so it might as well also convert from bool to TextDecorations.Underline.
This method keeps all the logic in the same file, unlike a converter, although a converter is more reusable. It also has the advantage of being easily unit-testable (unlike a data trigger).