How can you get a XAML TextBlock to collapse when it contains no data?

Question

I want to tell WPF: \"If TextBlock contains no data, then don\'t show it.\"

TRY #1 with a simple trigger produces

Answer 1

The easiest, simplest and quickest way are converters. So, why not KISS? (keep it simple, stupid)?

To implement converter classes only a few lines of code are necessary.

Converter:

public class StringToVisibilityConverter : IValueConverter
{
    public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
    {
        return string.IsNullOrWhiteSpace((string)value) ? Visibility.Collapsed : Visibility.Visible;
    }

    public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture)
    {
        var visiblity = (Visibility)value;
        return visiblity == Visibility.Visible;
    }
}

Usage:

Include namespace: xmlns:c="clr-namespace:Hfr.Windows.Controls"

Define resource: <c:StringToVisibilityConverter x:Key="StringToVisiblity"/>

Use it:

<TextBlock
    Text="{Binding SomeStringPropertyValue}"
    TextWrapping="Wrap"
    Visibility="{Binding SomeStringPropertyValue, Converter={StaticResource StringToVisiblity}}" />

Since you'll use your converters in multiple projects, implement the converter classes in a "common library".

Answer 2

I think the simplest way to do this would be to define a Converter which converts string to visibility.

   ...

   return string.IsNullOrEmpty(s) ? Visibility.Collapsed : Visibility.Visible;
}

Then just

<TextBlock Visibility="{StaticResource StringToVisibilityConverter}"

Answer 3

Either Try #2 or Try #3 should be fine - the problem is in the line where you are referencing the style - you need to use either 'Style="{StaticResource [KeyName]}"' or 'Style="{DynamicResource [KeyName]}"'.

Try this (in Try #2):

<StackPanel Margin="10">        
    <TextBlock Style="{StaticResource MainMessageStyle}" Padding="10" Background="Yellow" Text="{Binding MainMessage}"/>
</StackPanel>

In Try 1 you reveal a limitation of current WPF versions: Triggers are not supported directly on elements.