Question

我有一个IAppSettingsLoader接口，用于抽象文件IO以加载我的app.config文件。

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，试图监视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。这就是我试过的：

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);
}

此操作失败，因为Simple Injector无法将我的自定义ResolveCachedAppSettingsLoader识别为CachedAppSettingsLoader的实例工厂。

CachedAppSettingsLoader类型的构造函数包含参数类型为String的'cacheKey'，不能用于构造函数注射。参数名称：decoratorType

我的问题是如何在Simple Injector中提供自定义Func<CachedAppSettingsLoader>来构建这个缓存装饰器（带有依赖关系）？

Answer 1

Simple Injector不容易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来实现这种行为，但我想说有更简单的解决方案。

除了扩展Simple Injector之外，你在这里基本上有两个选择。您可以回退到手动构建对象图的这一部分，或者将原始配置值组提取到其自己的配置对象中，您可以在容器中注册为单例。

您可以手动构建装饰器及其装饰，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)
    {
        ...
    }
}

重构后，您可以按如下方式注册类型：

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

在Simple Injector中注册具有原始配置依赖性的装饰器

1 个答案: