WPF Tutorial | Localize using a MarkupExtension

The Idea

A simple and effective way to localize application resources is to write a custom MarkupExtension that provides a localized value. The extension takes a parameter in the constructor that is the unique resource key. When the DepdendencyProperty asks for the value. The markup extension looks up the value from the resource dictionary of your choice. This gives you the flexibility to use what you like as resource storage.

Using a custom markup extension has some advantages

Lightweight and powerful solution

Change languages at runtime

Free choice where to get the resources from.

How to use it

The usage of the markup extension is very simple. Just replace the string you want to localize by {l:Translate resourceKey}.

 
 <Window Title="{l:Translate Application.Title, DefaultValue=WPF Tutorial}" />

Implementing the markup extension

Important: The following code snipped shows a simplified example of an translate extension. A full-featured version is included in the sample solution.

 
[MarkupExtensionReturnType(typeof(string))]
public class TranslateExtension : MarkupExtension
{
    private string key;
    private DependencyObject targetObject;
    private DependencyProperty targetProperty;
 
    public TranslateExtension(string key)
    {
        this.key = key;
        Translator.CultureChanged += new EventHandler(Translator_CultureChanged);
    }
 
    void Translator_CultureChanged(object sender, EventArgs e)
    {
        if (targetObject != null && targetProperty != null)
        {
            targetObject.SetValue(targetProperty, 
                  Resources.ResourceManager.GetObject(key));
        }
    }
 
    public override object ProvideValue(IServiceProvider serviceProvider)
    {
        var targetHelper = (IProvideValueTarget)serviceProvider.
               GetService(typeof(IProvideValueTarget));
        targetObject = targetHelper.TargetObject as DependencyObject;
        targetProperty = targetHelper.TargetProperty as DependencyProperty;            
        return Resources.ResourceManager.GetObject(key);
    }
}
 
public static class Translator
{
    internal static event EventHandler CultureChanged;
 
    public static CultureInfo Culture
    {
        get
        {
            return Thread.CurrentThread.CurrentUICulture;
        }
        set
        {
            Thread.CurrentThread.CurrentUICulture = value;
            if (CultureChanged != null)
            {
                CultureChanged(null, EventArgs.Empty);
            }
        }
    }
}

Since there is no possibility to get notified, when the language of a thread changes, I created a static class called "Translator". Instead of switching the language directly on the Thread, I do it on the Translator. All TranslationExtensions register themself to the CultureChanged event of the Translator and re-set the localized value in the new language when the culture changes. That's all the trick.

Localize a WPF Application by using a MarkupExtension

The Idea

How to use it

Implementing the markup extension

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