Class Library with Dependency Injection

This article describes recommended practice for writing a localized class library that uses Depedency Injection.

Localization Sources

The class library may want to provide builtin localizations. The recommended practice is to create a public class AssetSources which implements IAssetSources as a signal to indicate that this class provides localizations for this class library.

Internal localization files are typically embedded resources.

using System.Collections.Generic;
using Lexical.Localization;
using Lexical.Localization.Asset;
using Microsoft.Extensions.FileProviders;

namespace TutorialLibrary2
{
    public class AssetSources : List<IAssetSource>, ILibraryAssetSources
    {
        /// <summary>
        /// Localization source reference to embedded resource.
        /// </summary>
        public readonly LineEmbeddedSource LocalizationSource = 
            LineReaderMap.Default.EmbeddedAssetSource(typeof(AssetSources).Assembly, "docs.TutorialLibrary2-de.xml");

        /// <summary>
        /// (Optional) External file localization source.
        /// </summary>
        public readonly LineFileProviderSource ExternalLocalizationSource;

        public AssetSources() : base()
        {
            // Add internal localization source
            Add(LocalizationSource);
        }

        public AssetSources(IFileProvider fileProvider) : this()
        {
            // Use file provider from dependency injection and search for an optional external localization source
            if (fileProvider != null)
            {
                ExternalLocalizationSource = 
                    XmlLinesReader.Default.FileProviderAssetSource(fileProvider, "Resources/TutorialLibrary2.xml", throwIfNotFound: false);
                Add(ExternalLocalizationSource);
            }
        }
    }
}

The example localization file TutorialLibrary2-de.xml.

<?xml version="1.0" encoding="UTF-8"?>
<Localization xmlns:Culture="urn:lexical.fi:Culture"
              xmlns:Type="urn:lexical.fi:Type"
              xmlns:Key="urn:lexical.fi:Key"
              xmlns="urn:lexical.fi">

  <!-- Example: Localization string for Culture "de" -->
  <Type:TutorialLibrary2.MyClass Culture="de">
    <Key:OK>Erfolgreich!</Key:OK>
  </Type:TutorialLibrary2.MyClass>

</Localization>

Classes

Classes in the class library can use IStringLocalizer abstractions

using Microsoft.Extensions.Localization;

namespace TutorialLibrary2
{
    public class MyClass
    {
        IStringLocalizer<MyClass> localizer;

        public MyClass(IStringLocalizer<MyClass> localizer)
        {
            this.localizer = localizer;
        }

        public string Do()
        {
            return localizer["OK"];
        }
    }
}

... or alternatively Lexical.Localization.Abstractions.

using Lexical.Localization;

namespace TutorialLibrary2
{
    public class MyClassB
    {
        ILine<MyClass> localizer;

        public MyClassB(ILine<MyClass> localizer)
        {
            this.localizer = localizer;
        }

        public string Do()
        {
            return localizer.Key("OK").Format("Operation Successful").ToString();
        }
    }
}

Application

Application that deploys the localizer must include the internal localizations with IAssetBuilder.AddAssetSources(Assembly) which searches the IAssetSources from the library.

• Snippet
• Full Code

// Create localizer
IAssetBuilder builder = new AssetBuilder.OneBuildInstance();
IAsset asset = builder.Build();
StringLocalizerRoot localizer = new StringLocalizerRoot(asset, new CulturePolicy());

// Install TutorialLibrary's IAssetSources
Assembly library = typeof(MyClass).Assembly;
builder.AddLibraryAssetSources(library).Build();

// Create class
IStringLocalizer<MyClass> classLocalizer = localizer.Type<MyClass>().AsStringLocalizer<MyClass>();
MyClass myClass = new MyClass(classLocalizer);

// Use the culture that was provided with the class library (AssetSources)
CultureInfo.CurrentCulture = CultureInfo.GetCultureInfo("de");
Console.WriteLine(myClass.Do());

Supplying Localizations

The application can supply additional localization sources with IAssetBuilder.AddSource(IAssetSource)

• Snippet
• Full Code

// Install additional localization that was not available in the TutorialLibrary.
IAssetSource assetSource = XmlLinesReader.Default.FileAssetSource("TutorialLibrary2-fi.xml");
builder.AddSource(assetSource).Build();

The example localization file TutorialLibrary2-fi.xml.

<?xml version="1.0" encoding="UTF-8"?>
<Localization xmlns:Culture="urn:lexical.fi:Culture"
              xmlns:Type="urn:lexical.fi:Type"
              xmlns:Key="urn:lexical.fi:Key"
              xmlns="urn:lexical.fi">

  <!-- Example: Localization string for Culture "fi" -->
  <Type:TutorialLibrary2.MyClass Culture="fi">
    <Key:OK>Toiminto onnistui!</Key:OK>
  </Type:TutorialLibrary2.MyClass>

</Localization>

When class is initialized with IServiceProvider, additional localizations are added to IServiceCollection as IAssetSources. Extension method AddLexicalLocalization(this IServiceCollection) adds the default services for localization.

• Snippet
• Full Code

IServiceCollection services = new ServiceCollection();

// Install file provider service
services.AddSingleton<IFileProvider>(s=>new PhysicalFileProvider(Directory.GetCurrentDirectory()));

// Install default IStringLocalizerFactory
services.AddLexicalLocalization(
    addStringLocalizerService: true,
    addCulturePolicyService: true,
    useGlobalInstance: false,
    addCache: false);

// Install TutorialLibrary's IAssetSources.
Assembly library = typeof(MyClass).Assembly;
services.AddLibraryAssetSources(library);

// Install additional localization that was not available in the TutorialLibrary.
services.AddSingleton<IAssetSource>(XmlLinesReader.Default.FileAssetSource("TutorialLibrary2-fi.xml"));

// Service MyClass
services.AddTransient<MyClass, MyClass>();

// Create instance container
using (var provider = services.BuildServiceProvider())
{
    // Create class
    MyClass myClass = provider.GetService<MyClass>();

    // Use the culture that was provided by with the class library (AssetSources)
    CultureInfo.CurrentCulture = CultureInfo.GetCultureInfo("de");
    Console.WriteLine(myClass.Do());

    // Use the culture that we supplied above
    CultureInfo.CurrentCulture = CultureInfo.GetCultureInfo("fi");
    Console.WriteLine(myClass.Do());
}