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,该接口抽象了文件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,试图监视文件对app.config的更改

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;
    }
}

我试图向Simple Injector注册此缓存装饰器,但未成功.这是我尝试的：

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);
}

之所以失败,是因为Simple Injector无法将我的自定义ResolveCachedAppSettingsLoader识别为CachedAppSettingsLoader的实例工厂.

The constructor of type CachedAppSettingsLoader contains parameter
‘cacheKey’ of type String which can not be used for constructor
injection. Parameter name: decoratorType

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

解决方法:

简单注入器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,但是我想说有更简单的解决方案.

除了扩展Simple Injector之外,这里基本上有两个选择.您可以退一步来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,您可以将其注册为容器中的单例.

您可以手动构造装饰器及其被装饰者,如下所示：

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

另一个选择是将配置值提取到其自己的类中,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)
    {
        ...
    }
}

重构之后,您可以按以下方式注册类型：

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

标签：dependency-injection,c,net,simple-injector
来源： https://codeday.me/bug/20191026/1934842.html