Localising text in MvvmCross ViewModels

Question

I'd like to get all my localised text from the ViewModels (as it's often dynamic), and I was wondering how you'd use a converter to get the text from the json files used for localisation. For instance, in the code below, I'd like LocalisedString to use the converter which I currently use in my Views in the bindings for static text -

public string MyText // used in the binding in the View
{
    get
    {
        string exclamation;

        if (MyValue <= 3.3)
        {
            exclamation = LocalisedString("Rubbish!");
        }
        else if (OverallScore > 3.3 && OverallScore <= 6.6)
        {
            exclamation = LocalisedString("Good!");
        }
        else
        {
            exclamation = LocalisedString("Excellent!");
        }

        return exclamation;
    }
}

Currently using version 1 of MvvmCross.

Any help much appreciated.

Answer 1

Note: this answer is about vNext - it should be fairly easy to port back to master... The differences in the area aren't that big.

---

There is a text localisation mechanism built into MvvmCross.

The only public sample that uses it is the Conference Sample.

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This sample includes shared and ViewModel specific Json files - see

These Json files each contain simple key-value pairs like:

{
"Title":"SQLBits X",
"Welcome":"Welcome",
"Sessions":"Sessions",
"Sponsors":"Sponsors",
"Tweets":"Tweets",
"Favorites":"Favorites"
}

They are linked in to Droid, Touch and WP as content or assets... all accessed by the platform using the ResourceLoader plugin.

---

To use these JSON files at runtime, the core project loads them up in the TextProviderBuilder:

    protected override IDictionary<string, string> ResourceFiles
    {
        get
        {
            var dictionary = this.GetType()
                .Assembly
                .GetTypes()
                .Where(t => t.Name.EndsWith("ViewModel"))
                .Where(t => !t.Name.StartsWith("Base"))
                .ToDictionary(t => t.Name, t => t.Name);

            dictionary[Constants.Shared] = Constants.Shared;
            return dictionary;
        }
    }

You could obviously easily load other JSON files here if you wanted to. It's not uncommon for some of my apps to have:

• a file for errors
• a file for general shared statements
• a file for specific components
• a file per ViewModel

While others have:

• just one big file!

Internationalisation - when it is done - is done by loading a different set of JSON files. Typically what is done is you load the default set first, then you load incremental overrides - so you might load English as default, Cat as an override and Cat-Lol as a further refinement.

For some discussions on this see:

• MvvmCross localization: switch at runtime
• and some future enhancements - https://github.com/slodge/MvvmCross/issues/55

---

Assuming you have one shared file and one file per ViewModel, then to provide runtime access to the text values from the JSON, the BaseViewModel presents 2 properties:

    public IMvxLanguageBinder TextSource
    {
        get { return new MvxLanguageBinder(Constants.GeneralNamespace, GetType().Name); }
    }

    public IMvxLanguageBinder SharedTextSource
    {
        get { return new MvxLanguageBinder(Constants.GeneralNamespace, Constants.Shared); }
    }

These properties are used in data binding using:

• Path specifying whether to use SharedTextSource or TextSource
• MvxLanguageBinderConverter as the Converter
• the text key as the ConverterParameter

For example, in Droid this is :

<TextView
  style="@style/AboutPageBodyText"
  local:MvxBind="{'Text':{'Path':'TextSource','Converter':'Language','ConverterParameter':'Title'}}"
  />

Although in modern 'Swiss' binding this would be written as:

<TextView
  style="@style/AboutPageBodyText"
  local:MvxBind="Text TextSource, Converter=Language, ConverterParameter='Title'"
  />

Any code which wishes to use the Text can also do it - see for example how the TimeAgo text is created from resource strings in TimeAgoConverter.cs which uses resource strings like:

{
"TimeAgo.JustNow":"just now",
"TimeAgo.SecondsAgo":"{0}s ago",
"TimeAgo.MinutesAgo":"{0}m ago",
"TimeAgo.HoursAgo":"{0}h ago",
"TimeAgo.DaysAgo":"{0}d ago",
"TimeAgo.Never":"never"
}

The code for this is effectively:

 var valueToFormat = 42;
 var whichFormat = "TimeAgo.DaysAgo";

 var textProvider = this.GetService<IMvxTextProvider>();
 var format = textProvider.GetText(Constants.GeneralNamespace, Constants.Shared, whichFormat);

 return string.Format(format, valueToFormat)

---

The language Binder and the ValueConverter are really very simple code

• MvxLanguageBinder.cs
• MvxLanguageBinderConverter.cs

So feel free to build something more sophisticated for your app if you need it.

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Other cross-platform text localisation techniques are available - I myself would particularly like to try Vernacular one day - https://github.com/rdio/vernacular