带有额外依赖的简单注入器装饰

Question

我有一个装饰器 SomethingLoggerDecorator，它应该用日志记录装饰 ISomething 实例：

public class SomethingLoggerDecorator : ISomething
{
    private readonly ISomething decoratee;
    private readonly ILogger logger;

    public SomethingLoggerDecorator(ISomething decoratee, ILogger logger)
    {
        this.decoratee = decoratee;
        this.logger = logger;
    }

    public void DoSomething()
    {
        this.logger.Info("Doing Something");
        this.decoratee.DoSomething();
    }

    public void DoSomethingElse(string withThis)
    {
        this.logger.Info("Doing Something Else with " + withThis);
        this.decoratee.DoSomethingElse(withThis);
    }
}

如何使用 Simple Injector 用 SomethingLoggerDecorator 装饰 ISomething 的实例，并使用静态工厂方法 LogManager.GetLogger(decoratee.GetType()) 将 ILogger 的实例注入到每个装饰器中，其中 decoratee 是要执行的实际实例被装饰？此外，注入的ILogger 和SomethingLoggerDecorator 的生命周期应始终与被装饰者的生命周期相匹配。

Answer 1

在 Simple Injector 中有多种方法可以做到这一点。

首先，您可以让装饰器的构造函数依赖于DecoratorContext 类。 DecoratorContext 包含有关装饰器的上下文信息。它包含诸如包装装饰器的类型和被装饰的实际实现的类型（真实实例）等信息。所以你的装饰器可能如下所示：

public class SomethingLoggerDecorator : ISomething
{
    private readonly ISomething decoratee;
    private readonly DecoratorContext context;

    public SomethingLoggerDecorator(ISomething decoratee, DecoratorContext context)
    {
        this.decoratee = decoratee;
        this.context = context;
    }

    public void DoSomething()
    {
        var logger = LogManager.GetLogger(this.context.ImplementationType);
        logger.Info("Doing Something");
        this.decoratee.DoSomething();
    }
}

使用这个DecoratorContext 类的缺点是你的装饰器需要依赖于简单注入器，这基本上意味着你必须将装饰器移动到你的Composition Root 中以防止你的应用程序依赖于DI 库。你可以找到更多关于使用这个DecoratorContext类here的信息。

另一种选择是使您的装饰器通用，并为可以生成正确装饰器的RegisterDecorator 重载之一提供装饰器类型工厂。例如：

public class SomethingLoggerDecorator<TImplementation> : ISomething
{
    private readonly ISomething decoratee;

    public SomethingLoggerDecorator(ISomething decoratee)
    {
        this.decoratee = decoratee;
    }

    public void DoSomething()
    {
        var logger = LogManager.GetLogger(typeof(TImplementation));
        logger.Info("Doing Something");
        this.decoratee.DoSomething();
    }
}

或可选：

public class SomethingLoggerDecorator<TImplementation> : ISomething
{
    private readonly ISomething decoratee;
    private readonly ILogger<TImplementation> logger;

    public SomethingLoggerDecorator(ISomething decoratee, ILogger<TImplementation> logger)
    {
        this.decoratee = decoratee;
        this.logger = logger;
    }

    public void DoSomething()
    {
        this.logger.Info("Doing Something");
        this.decoratee.DoSomething();
    }
}

使用这两种实现，您可以按如下方式注册装饰器：

container.RegisterDecorator(typeof(ISomething),
    c => typeof(SomethingLoggerDecorator<>).MakeGenericType(c.ImplementationType),
    Lifestyle.Transient,
    predicate: c => true);

使用第二个实现，您会将问题稍微转移到通用的ILogger<T> 抽象上，但实现可能如下所示：

public class Log4netAdapter<T> : ILogger<T>
{
    public void Log(LogEntry entry) {
        var logger = LogManager.GetLogger(typeof(T));
        // TODO: log
    }
}