Adding StringFormat to TranslateExtension

If you're tasked with adding localization to your Xamarin Application you may start with the TranslateExtension example from Xamarin. This allows you to add String Resources to your AppResources.resx file and consume them using XAML or C#.

This solution works well until you need to append a colon or any character to one of your String Resources. In the example below, we have Name & Special Ability on both pages. On the List Page the text is appended with a colon.

Now let's take a look at what the String Resources & XAML would look like:

Without StringFormat

<Label Text="{local:Translate Name}" />
<Label Text="{local:Translate NameWithColon}" />

As you can see, this is going to lead to duplicate resources which in a larger application would be a nightmare to maintain.

With StringFormat

<Label Text="{local:Translate Name}" />
<Label Text="{local:Translate Name, StringFormat='{0}:'}" />

Much better.

Adding String Format Property to Translate Extension

This part is rather simple. You'll need to add a StringFormat property to the TranslateExtension.cs class and apply the format in the ProvideValue method.

[ContentProperty("Text")]
public class TranslateExtension : IMarkupExtension
{
    readonly CultureInfo ci = null;
    const string ResourceId = "LocalizationWithStringFormat.Resources.AppResources";

    static readonly Lazy<ResourceManager> ResMgr = new Lazy<ResourceManager>(() => new ResourceManager(ResourceId, IntrospectionExtensions.GetTypeInfo(typeof(TranslateExtension)).Assembly));

    public string Text { get; set; }
    public string StringFormat { get; set; }

    public TranslateExtension()
    {
        if (Device.RuntimePlatform == Device.iOS || Device.RuntimePlatform == Device.Android)
        {
            ci = DependencyService.Get<ILocalize>().GetCurrentCultureInfo();
        }
    }

    public object ProvideValue(IServiceProvider serviceProvider)
    {
        if (Text == null)
            return string.Empty;

        var translation = ResMgr.Value.GetString(Text, ci);
        if (translation == null)
        {
#if DEBUG
            throw new ArgumentException(
                string.Format("Key '{0}' was not found in resources '{1}' for culture '{2}'.", Text, ResourceId, ci.Name),
                "Text");
#else
            translation = Text; // HACK: returns the key, which GETS DISPLAYED TO THE USER
#endif
        }

        if (!string.IsNullOrWhiteSpace(StringFormat))
        {
            return string.Format(StringFormat, translation);
        }

        return translation;
    }
}

Simple.