使用Unity将对象注入到IValueConverter实例中

Question

我在Silverlight5项目中有一个IValueConverter实例，它可以将自定义数据转换为不同的颜色。我需要从数据库中读取实际的颜色值(因为用户可以编辑这些颜色值)。

由于Silverlight使用异步调用通过实体框架从数据库加载数据，因此我创建了一个简单的存储库，它保存来自数据库的值。

接口：

public interface IConfigurationsRepository
{
    string this[string key] { get; }
}

实现：

public class ConfigurationRepository : IConfigurationsRepository
{
    private readonly TdTerminalService _service = new TdTerminalService();

    public ConfigurationRepository()
    {
        ConfigurationParameters = new Dictionary<string, string>();
        _service.LoadConfigurations().Completed += (s, e) =>
            {
                var loadOperation = (LoadOperation<Configuration>) s;
                foreach (Configuration configuration in loadOperation.Entities)
                {
                    ConfigurationParameters[configuration.ParameterKey] = configuration.ParameterValue;
                }
            };
    }

    private IDictionary<string, string> ConfigurationParameters { get; set; }

    public string this[string key]
    {
        get
        {
            return ConfigurationParameters[key];
        }
    }
}

现在我想使用Unity将我的存储库的这个实例注入到IValueConverter实例中……

App.xaml.cs：

private void RegisterTypes()
{
    _container = new UnityContainer();
    IConfigurationsRepository configurationsRepository = new ConfigurationRepository();
    _container.RegisterInstance<IConfigurationsRepository>(configurationsRepository);
}

IValueConverter：

public class SomeValueToBrushConverter : IValueConverter
{
    [Dependency]
    private ConfigurationRepository ConfigurationRepository { get; set; }

    public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
    {
       switch ((SomeValue)value)
        {
            case SomeValue.Occupied:
                return new SolidColorBrush(ConfigurationRepository[OccupiedColor]);
            default:
                throw new ArgumentException();
        }
    }

    public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture)
    {
        throw new NotImplementedException();
    }
}

问题是，我在转换器实例中没有得到相同的Unity-Container (即，存储库未注册)。

Answer 1

根据您的评论，您需要使用ServiceLocator来获取ConfigurationRepository的实例，因为转换器的实例不是由Unity创建的，而是由Silverlight/XAML引擎创建的。

所以你的用DependencyAttribute装饰的属性不会被注入。

c#

public class SomeValueToBrushConverter : IValueConverter
{
    public SomeValueToBrushConverter(){
      ConfigurationRepository = ServiceLocator.Current.GetInstance<ConfigurationRepository>();
    }

    private ConfigurationRepository ConfigurationRepository { get; set; }
}

在您的RegisterTypes方法中，您需要配置ServiceLocator：

_container = new UnityContainer();
UnityServiceLocator locator = new UnityServiceLocator(_container);
ServiceLocator.SetLocatorProvider(() => locator);

Answer 2

可以使用MarkupExtension解析DI容器中的依赖关系：

public class IocResolver : MarkupExtension
{
    public IocResolver()
    { }

    public IocResolver(string namedInstance)
    {
        NamedInstance = namedInstance;
    }

    [ConstructorArgument("namedInstance")]
    public string NamedInstance { get; set; }

    public override object ProvideValue(IServiceProvider serviceProvider)
    {
        var provideValueTarget = (IProvideValueTarget)serviceProvider
            .GetService(typeof(IProvideValueTarget));

        // Find the type of the property we are resolving
        var targetProperty = provideValueTarget.TargetProperty as PropertyInfo;

        if (targetProperty == null)
            throw new InvalidProgramException();

        Debug.Assert(Resolve != null, "Resolve must not be null. Please initialize resolving method during application startup.");
        Debug.Assert(ResolveNamed != null, "Resolve must not be null. Please initialize resolving method during application startup.");

        // Find the implementation of the type in the container
        return NamedInstance == null
            ? (Resolve != null ? Resolve(targetProperty.PropertyType) : DependencyProperty.UnsetValue)
            : (ResolveNamed != null ? ResolveNamed(targetProperty.PropertyType, NamedInstance) : DependencyProperty.UnsetValue);
    }

    public static Func<Type, object> Resolve { get; set; }
    public static Func<Type, string, object> ResolveNamed { get; set; }
}

IocResolver必须在应用程序启动期间进行初始化，如下所示：

IocResolver.Resolve = kernel.Get; 
IocResolver.ResolveNamed = kernel.GetNamed;
// or what ever your DI container looks like

之后，您可以在XAML中使用它来在XAML中注入依赖：

<!-- Resolve an instance based on the type of property 'SomeValueToBrushConverter' -->
<MyConverter SomeValueToBrushConverter="{services:IocResolver}" />

<!-- Resolve a named instance based on the type of property 'SomeValueToBrushConverter' and the name 'MyName' -->
<MyConverter SomeValueToBrushConverter="{services:IocResolver  NamedInstance=MyName}" />