WPF Label adapt FontSize to it's Width and Height

Question

I need to develop a Label control in WPF, on .NET 3.5 and VisualStudio 2010, in which the FontSize will automatically make the text fill the control area.

I don't know if I should create a CustomControl inheriting from Label or if I should create a UserControl which contains a Label control.

I've seen an example here using a ValueConverter, but I'm not understanding its behavior, here: change font size dynamically.

Can anyone give me a clue about that?

Update:

I found the solutiion using the DoubleConverter from the example I've posted before:

The soultion is using a ValueConverter, which I extracted from the example, but added the NumerFormat IFormatProvider to correctly parse "0.1" value, I found that at Decimal d1 = Decimal.Parse("0.1"); // = 1?!?:

 [ValueConversion(typeof(object), typeof(double))]
 public class DoubleConverter : IValueConverter
 {
  public object Convert(object value, Type targetType,
   object parameter, CultureInfo culture)
  {
   double dblValue = (double)value;
   double scale = Double.Parse(((string)parameter), System.Globalization.CultureInfo.InvariantCulture.NumberFormat);
   return dblValue * scale;
  }

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

Then, you have to instantiate in XAML the DoubleConverter, and specify the binding in the FonSize Property:

<UserControl x:Class="<Namespace>.LabelAutoFontSize"
  xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
  xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
  xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006" 
  xmlns:d="http://schemas.microsoft.com/expression/blend/2008" 
  xmlns:me="clr-namespace:<Namespace>"
  mc:Ignorable="d" 
  d:DesignHeight="60" d:DesignWidth="278">
 <UserControl.Resources>
 <me:DoubleConverter x:Key="doubleConverter" />
 </UserControl.Resources>
 <Grid>
 <Label
  x:Name="lbl"
  FontSize="{
   Binding Path=Width,
    RelativeSource={RelativeSource AncestorType={x:Type UserControl}},
   Converter={StaticResource doubleConverter},
   ConverterParameter=0.116}"

  VerticalAlignment="Stretch"
  HorizontalAlignment="Stretch"
  Content="LabelAutoFontSize"
  d:LayoutOverrides="Width"
  HorizontalContentAlignment="Center"
  VerticalContentAlignment="Center" />
 </Grid>
</UserControl>

An important point is that the value for ConverterParameter depends absolutely from the font assigned. Each font may need a different value and you have to "play around" to get the correct value to fit exactly.

Solution

<Viewbox>
    <TextBlock>asd</TextBlock>
</Viewbox>

Also does the job.

Comments

[cplotts]

Don't forget that you can also use StretchDirection to only resize down when it doesn't fit ... but leave it alone when it does fit.

[reuscam]

While the viewbox trick works, it also resizes already rendered text, which may not be as sharp as if it were actually rendered to the appropriate size.

[Alex Maker]

@reuscam: I don't think it's the way the viewbox works. It doesn't resize already rendered content, it applies transformations that are used when the content is rendered. At least I hope it does so, because it's part of WPF's rendering concept.