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Dan Wahlin

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Text Trimming in Silverlight 4

May 06, 2010

Silverlight 4 has a lot of great features that can be used to build consumer and Line of Business (LOB) applications. Although Webcam support, RichTextBox, MEF, WebBrowser and other new features are pretty exciting, I'm actually enjoying some of the more simple features that have been added such as text trimming, built-in wheel scrolling with ScrollViewer and data binding enhancements such as StringFormat. In this post I give a quick introduction to a simple yet productive feature called "text trimming" and show how it eliminates a lot of code compared to Silverlight 3.

The TextBlock control contains a new property in Silverlight 4 called TextTrimming that can be used to add an ellipsis (…) to text that doesn't fit into a specific area on the user interface. Before the TextTrimming property was available I used a value converter to trim text which meant passing in a specific number of characters that I wanted to show by using a parameter:

public class StringTruncateConverter : IValueConverter
    #region IValueConverter Members
    public object Convert(object value, Type targetType, object parameter, 
     System.Globalization.CultureInfo culture)
        int maxLength;
        if (int.TryParse(parameter.ToString(), out maxLength))
            string val = (value == null) ? null : value.ToString();
            if (val != null && val.Length > maxLength)
                return val.Substring(0, maxLength) + "..";
        return value;
    public object ConvertBack(object value, Type targetType, 
     object parameter, System.Globalization.CultureInfo culture)
        throw new NotImplementedException();

To use the StringTruncateConverter I'd define the standard xmlns prefix that referenced the namespace and assembly, add the class into the application's Resources section, and then use the class while data binding:

<TextBlock Grid.Column="1" Grid.Row="3" ToolTipService.ToolTip="{Binding 
  ReportSummary.ProjectManagers}" Text="{Binding 
  Converter={StaticResource StringTruncateConverter},ConverterParameter=16}" 
  Style="{StaticResource SummaryValueStyle}" />

With Silverlight 4 I can define the TextTrimming property directly in XAML or use the new Property window in Visual Studio 2010 to set it to a value of WordEllipsis (the default value is None):

<TextBlock Grid.Column="1" Grid.Row="4" 
  ToolTipService.ToolTip="{Binding ReportSummary.ProjectCoordinators}" 
  Text="{Binding ReportSummary.ProjectCoordinators}" 
  TextTrimming="WordEllipsis"  Style="{StaticResource SummaryValueStyle}"/>

The end result is a nice trimming of the text that doesn't fit into the target area as shown with the Coordinator and Foremen sections below. My data binding statements are now much smaller and I can eliminate the StringTruncateConverter class completely.

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