c# - 在 Simple Injector 中注册具有原始配置依赖项的装饰器

我有一个 IAppSettingsLoader 接口(interface)，它抽象了用于加载我的 app.config 文件的文件 IO。

public interface IAppSettingsLoader
{
    IEnumerable<KeyValuePair<string, string>> LoadAppSettings();
}

我有一个加载实际文件的类:

public class FileAppSettignsLoader : IAppSettingsLoader
{
    public IEnumerable<KeyValuePair<string, string>> LoadAppSettings()
    {
        // Perform actual loading through ConfigurationManager.AppSettings
    }
}

然后我有一个缓存装饰器，它试图监视对 app.config 的文件更改

public class CachedAppSettingsLoader : IAppSettingsLoader
{
    private readonly ObjectCache _cache;
    private readonly string _cacheKey;
    private readonly CacheItemPolicy _cacheItemPolicy;
    private readonly IAppSettingsLoader _innerAppSettingsLoader;

    public CachedAppSettingsLoader(ObjectCache cache,
                                   string cacheKey,
                                   CacheItemPolicy cacheItemPolicy,
                                   IAppSettingsLoader innerAppSettingsLoader)
    {
        _cacheKey = cacheKey;
        _cacheItemPolicy = cacheItemPolicy;
        _cache = cache;
        _innerAppSettingsLoader = innerAppSettingsLoader;
    }

    public IEnumerable<KeyValuePair<string, string>> LoadAppSettings()
    {
        object cached = _cache[_cacheKey];
        if (cached != null)
        {
            return (IEnumerable<KeyValuePair<string, string>>)cached;
        }

        var keyValuePairs = _innerAppSettingsLoader.LoadAppSettings();

        // _cacheItemPolicy will contain a HostFileChangeMonitor
        _cache.Add(_cacheKey, keyValuePairs, _cacheItemPolicy);
        return keyValuePairs;
    }
}

我试图用 Simple Injector 注册这个缓存装饰器，但没有成功。这是我尝试过的:

private void RegisterDependencies(Container container)
{
    container.RegisterSingleton(() =>
        ResolveCachedAppSettingsLoader(container));
    container.Register<IAppSettingsLoader, FileAppSettingsLoader>(
        Lifestyle.Singleton);
    container.RegisterDecorator<IAppSettingsLoader, CachedAppSettingsLoader>(
        Lifestyle.Singleton);
}

private CachedAppSettingsLoader ResolveCachedAppSettingsLoader(Container container)
{
    var cacheItemPolicy = new CacheItemPolicy();
    cacheItemPolicy.ChangeMonitors.Add(new HostFileChangeMonitor(new[] { "app.config" }));

    var innerAppSettingsLoader = container.GetInstance<IAppSettingsLoader>();
    return new CachedAppSettingsLoader(
        "AuthorizationRecords",
        cacheItemPolicy,
        MemoryCache.Default,
        innerAppSettingsLoader);
}

这失败是因为 Simple Injector 无法将我的自定义 ResolveCachedAppSettingsLoader 识别为 CachedAppSettingsLoader 的实例工厂。



我的问题是如何提供自定义 Func<CachedAppSettingsLoader> 以在 Simple Injector 中构造此缓存装饰器(带有依赖项)？

最佳答案

Simple Injector 不允许注册包含原始配置值的装饰器。有多种方法可以扩展 Simple Injector 以启用此类行为，但我想说有更简单的解决方案。

除了扩展 Simple Injector 之外，您在这里基本上有两个选择。您要么回退到对象图的这一部分的手动构建，要么将原始配置值组提取到其自己的配置对象中，您可以将其注册为容器中的单例。

您可以手动构建装饰器及其被装饰者，如下所示:

container.RegisterSingleton<IAppSettingsLoader>(
    new CachedAppSettingsLoader(
        "AuthorizationRecords",
        cacheItemPolicy,
        MemoryCache.Default,
        new FileAppSettingsLoader()));

另一种选择是将配置值提取到它自己的类中，无论如何这可能是个好主意:

public class CachedAppSettingsLoaderSettings
{
    public ObjectCache Cache;
    public CacheItemPolicy Policy;
    public string CacheKey;
}

public class CachedAppSettingsLoader : IAppSettingsLoader
{
    private readonly CachedAppSettingsLoaderSettings settings;
    private readonly IAppSettingsLoader decoratee;

    public CachedAppSettingsLoader(
        CachedAppSettingsLoaderSettings settings, IAppSettingsLoader decoratee)
    {
        ...
    }
}

在此重构之后，您可以按如下方式注册您的类型:

container.Register<IAppSettingsLoader, FileAppSettingsLoader>(Lifestyle.Singleton);
container.RegisterDecorator<IAppSettingsLoader, CachedAppSettingsLoader>(
    Lifestyle.Singleton);
container.RegisterInstance(new CachedAppSettingsLoaderSettings
{
    Cache = MemoryCache.Default,
    Policy = new CacheItemPolicy { ... },
    CacheKey = "AuthorizationRecords"
});

关于c# - 在 Simple Injector 中注册具有原始配置依赖项的装饰器，我们在Stack Overflow上找到一个类似的问题：https://stackoverflow.com/questions/42406713/